KENWOOD TS-940 PAGE

Page 1 of 151
Version 2: 4 April 2005, Version 3: 25 April 2005, Version 4: 27 May 2005, Version 5: 31May 2005, Version 6: 10 June 2005: Version 7: 16 June 2005: Version 8: 25 July 2005Version 9: 30 July 2005. Version 10: 4 August 2005, Version 11: 13 Sep 2005, Version 12: 18 October 2005, Version 13: 23 October 2005, Version 14: 22 March 2006, Version15: * April 2006
From a passionate Kenwood TS-940 owner. The 940 has to be one of the greatest transceivers ever produced. This page is provided because: Some information here is not available anywhere else and should be useful to any TS-940 owner, Information does not exist in a single web site which is easy to follow, If the information remains available more TS-940s will be repaired and functional, (and probably improved), The intention is to acknowledge the person who discover the information so questions can be sent to that person. When information is already well documented and reliably maintained on another site then a hyperlink is made to that site to avoid yet another slightly different version. I will publish all email feedback at the end of the page, so that whatever is discovered by others can be shared by all. Please email to jaking@es.co.nz Yours sincerely Jeff King ZL4AI / DU7
Disclaimer: No liability or responsibility whatsoever is taken for any of the information on this site. You assume total liability for any modification you undertake. Copyright: Everything on this page
What is new in Version 15:
SUMMARY OF R149 AND R150 MIS-LABELLING
What is new in Version 14:
BATTERIES: [INTERNAL] BATTERY REPLACEMENT CW FILTERS

Motor bearings gummed up

http://homepages.ihug.co.nz/~jaking/TS-940_02.htm

5/14/2006

Page 2 of 151
Field measurements of receiver improvement following FET swap
What is new in Version 13:
PROMOTIONAL BROCHURE SERVICE MANUAL & SERIAL NUMBERS
What is new in Version 12:

PLL BOARD 4: PLL BOARD

RF BOARD

OUT OF LOCK

AVR BOARD & POWER SUPPLY FAN AND TEMPERATURES COOL AVR COMPONENTS BY REMOUNTING ON HEAT SINK POWER SUPPLY HEAT SINK RUNS TOO HOT VERIFY THERMISTOR 101 IS ATTACHED AND FUNCTIONING
PROMOTIONAL BROCHURE RECEIVER PERFORMANCE IMPROVEMENTS. R1. KENWOOD PRODUCED 3 SERVICES BULLETINS WHICH DO CONSIDERABLY IMPROVE THE RECEIVER. RECEIVER 2. FIELD EFFECT TRANSISTORS AROUND THE WRONG WAY. RECEIVER 3. THERE IS NO AGC TIMING CORRECTION SUMMARY OF R149 AND R150 MIS-LABELLING Mike KC8ZNW on 25/4/05 describes this same behaviour to the Kenwood.net. Executive Summary of AGC Mod Independent Feedback on how Receiver Improves THE PRODUCTION MISTAKE DESCRIBED: TO CHANGE THE RESISTORS THE INITIAL PROBLEM SYMPTOMS: ACKNOWLEDGEMENTS TO PERSONS WHO HELPED SOLVE THIS A CAUTION: COMMUNICATIONS WITH KENWOOD JAPAN BELOW: RECEIVER 4. PIN DIODE IMPROVEMENTS 4.1: Background on how Pin Diodes were discovered to improve radios. 4.2 RadCom Technical Topics explains what Pin Diodes were supposed to achieve. Intermodulation properties of switching diodes, by Dr. Ing. Jochen Jirmann, DB1NV 4.3: Summary of Key points on Purpose of Pin Diodes: [by ZL4AI] 4.4 Experience from Persons who modified the TS-940 4.5 : Pin Diode Modification for TS-440 4.6: So summary of Pin Diode Modification PLL BOARD PROBLEMS

Page 3 of 151

PLL PLL PLL PLL PLL
BOARD 0: BOARD 1: BOARD 2: BOARD 3: BOARD 4:
RESEAT CONNECTORS REMOVE THE BLACK FOAM FROM BEHIND THE BOARD REMOVE THE WAX FROM THE VCOS IDENTIFY WHICH PLL IS NOT LOCKED PLL BOARD AND RF BOARD AND PLL OUT OF LOCK
CONTROL BOARD VOLTAGE REGULATOR HEATS UP AND CAUSES A SHIFT IN BFO ON IF BOARD AVR BOARD & POWER SUPPLY FAN AND TEMPERATURES COOL AVR COMPONENTS BY REMOUNTING ON HEAT SINK POWER SUPPLY HEAT SINK RUNS TOO HOT VERIFY THERMISTOR 101 IS ATTACHED AND FUNCTIONING REPLACE Q101 AND Q 102 MOTOR BEARINGS GUMMED UP: TEMPORARY FIX RF BOARD 1: BOARD RUNS VERY HOT HOW IT WORKS AM MODE: HOW TO VERIFY ITS SWITCHED IN FM MODE: SETTING FM CARRIER CW FILTERS SERVICE MANUAL & SERIAL NUMBERS IDENTIFYING WHEN RADIO MANUFACTURED BULBS CONNECTOR PROBLEMS BATTERIES: [INTERNAL] BATTERY REPLACEMENT INFORMATION NOT ANNOUNCED BY KENWOOD: KENWOOD RELEASED INFORMATION: S METER ALIGNMENT LEVELS PARTS LINKS TO USEFUL SITES HELP WANTED PERFORMANCE COMPARISONS MODIFICATIONS POWER SUPPLY IMPROVEMENTS ALC DELAY TIME: TS-940 AVERAGE OUTPUT POWER SSB USE OF TS940S FSK RECEIVE FOR HF PACKET INQUIRY REGARDING USE OF ADDITIONAL RECVR. GEIL CHIP FEEDBACK FROM READERS

Page 4 of 151

PROMOTIONAL BROCHURE

Page 5 of 151

Page 6 of 151

Page 7 of 151

Page 8 of 151

Page 9 of 151

Page 10 of 151

Page 11 of 151

Page 12 of 151

Page 13 of 151

Page 14 of 151

Page 15 of 151

Independent Feedback on how Receiver Improves
1. From: Ed [mailto:ca.urso2@verizon.net] Sent: Monday, 23 May 2005 7:18 a.m. To: jaking@es.co.nz Subject: TS-940S Also, your AGC Timing Correction was applied on my rig (SN 806XXXX) and worked great! Sure enough, resistors R149 (68K on my equip) and R150 2.2Meg had been incorrectly installed by the Mfr. The board markings for those resistors were wrong. 73, Ed Alves KD6EU USA
Full email at: FeedbacK_3

Page 43 of 151

From: el34guy@aol.com [mailto:el34guy@aol.com] Sent: Thursday, 23 June 2005 4:46 p.m. To: jaking@es.co.nz Subject: agc modification Hi Jeff, I was looking through the 940 page and found my feedback to you(regarding the AGC modification with resistors 149 and 150) under the alc setting portion. Im sure I mislabeled my original email to you on this (think I wrote alc). I am having some luck with changing out the 2.2 meg for a 1 meg resistor. Im thinking maybe a little lower value might be worthwhile to test also, like a 6-800k ohm value. I know I received another email from you on this but I just wanted to let you know it looked like my feedback was in the wrong spot on your page. -----Original Message----From: el34guy@aol.com [mailto:el34guy@aol.com] Sent: Sunday, 12 June 2005 9:43 p.m. To: jaking@es.co.nz Subject: Re: alc mod Jeff I thought that mod might be a little better than it was for the alc. It made my radio appear as if it was in fast agc mode all the time. There wasnt a lot of smoothness in the ssb signal that Im used to. Like I said, maybe something like a 1.1 meg is worth considering in there. There isnt much room to solder at all in there. Geez, its tight. 73 Mark
[Editors Note: ZL4AI questions the validity of these observations but has included them to keep feedback information unbiased. Varying the resistors from Kenwoods values was never recommended or intended. With resistors changed around on the Editors 940 AGC slow is still very much slower than AGC fast.]
-----Original Message----From: Michael Feryok II [mailto:mikeferyok@yahoo.com] Sent: Saturday, 9 July 2005 9:57 a.m. To: jaking@es.co.nz Subject: AGC Mod Hey Jeff, Thanks so much for your TS940 page it helped a co-worker and I today to swap the R149-150 resistors for the AGC mod. Very apparent improvement in noise level and gain. I can hear stations that are buried into the noise floor now. Mike, KC8ZNW From: ts-940@yahoogroups.com [mailto:ts-940@yahoogroups.com] On Behalf Of mikeferyok Sent: Saturday, 9 July 2005 9:53 a.m. To: ts-940@yahoogroups.com Subject: [ts-940] AGC mod works great!! My friend and I did the R149-R150 swap and it improved the gain and noise level. Adjusted the VR3 for a proper zero on the meter and

Page 54 of 151

R149 68K R150 2.2M Specified in Revised Service Manual: R149 150K R150K 2.2M Resistors as actually installed on my board if you follow the logic of the circuit diagram. R149 2.2M R150 150K I have two IF boards here and they both have the resistors installed as required by the screen printing and hence on both boards both resistors are reversed. Possibly this is the case for every TS-940 ever made. I cannot understand how the circuits would function as the designer intended, as the installed resistors are very different to those shown on the schematic diagrams. Could you please advise if my observation is correct, and after later when Kenwood has investigated if it would be advisable to swap R149 with R 150 and vice versa? At this time could you please just confirm that the question will be investigated? I look forward to your reply. Yours sincerely Jeff King ZL4AI

RECEIVER 4.

PIN DIODE IMPROVEMENTS
This improvement is not fully documented yet. Please send in information.
4.1: Background on how Pin Diodes were discovered to improve radios.
[TenTec] Pin Diodes / Paragon Chester Alderman chestert@pressroom.com Wed, 17 Sep 1997 17:14:45 -0400
TenTec builds a great amateur radio and obviously to give you a 'million dollar radio' that cost the user five bucks, picture. PIN diodes have been around for many years, however they were initially invented, designed, manufactur devices, obviously because you can not use mechanical relays for internal switching within a microwave RF circui frequency' device until within the last 20 years or so. Dont quote me on this because I've been out of microwave design for too long. A regular diode is a piece of silicon side of the junction is doped, during mfg process, to have an excess of electrons (+P) and the other side of the diod therefore the term PN junction. And of course a PN junction diode will pass current (a signal) in only one direction characteristics (but each side is doped differently than than a standard diode), and in addition, between the +P and t doped specifically to allow the diode to switch VERY rapidly, and this region is called the Intrensic junction, thus

Page 55 of 151

can switch is basically determined by the width of this Intrensic area, the narrower the I junction, the faster it will s frequency that you can pass throught it. Unfortunately, to build a PIN diode that will switch at HF freqs (below 30 or the diode will switch too fast to allow one cycle of an HF signal to pass through it. What all of this means is that PIN diodes are relatively expensive. A regular PN junction diode (typically a 1N4148 however a 'cheap' true PIN diode will cost between one and three dollars apiece; and thats why you do not see them ECONOMICS. (I'm not sure why it took that much verbage to explain, but it did.) Corsair II's used a regular silicon switching diode, 1N4148 to switch the filters. The Omni 6 does use PIN diodes, b mentioned economics, TenTec uses diodes that 'will do the job' verses expensive PIN diodes. I read Rhode's article on PIN diodes and decided I could improve the IM performance of my Omni 6 (it didn't need Packard PIN diodes that Rhode stated were the best, and installed them in my Omni 6. Over the past five years usin in some serious DX contest, I have yet failed to see where these expensive HP PIN diodes made any substantial im TenTec runs about 10ma of current through their production PIN diodes, in order to gain the full IM advantage of t through the HP PIN diodes! So the bottom line is if you replace the PIN or silicon diodes in a rig, you will see (hear) practically no improvemen utilize the diodes operating at their optimum design specifications. Probably if you find the filter switching diodes probably means that someone has taken the time to change the current running through the switching diodes to real

Page 67 of 151

"Finally, there is no question that relays provide the best of all worlds as far as IMD characteristics are concerned, but not necessarily the best solution in terms of space and costs. 1 have just tested a soon-to-be-re leased transceiver which uses PIN-type di odes and exhibits superb IMD characteristic while maintaining a good noise figure. "As to multi-tone functionality, once 2n and 3rd order IMD tests have been done, on can predict the higher-order IMD effects, especially since they are based on diode characteristics and this type of test is a legitimate test to evaluate receivers. "Hopefully, your readers will not deduct from this experiment that QST or other reputable magazines publish articles which are technically incorrect." In a subsequent letter, dated September 19, 1995, Dr Rohde confirms that he has run into a lot of people who have modified their RF switching diodes and have been extremely happy with the results. Further, after refining his test set-up he finds the improvement is now slightly more dramatic than outlined in his QST article. In regard to Dr Rohde's endorsement of the technical accuracy of articles, I would enter a caveat. While most writers strive lo complete accuracy. the mechanics an Murphy's Law of publication make it difficult to avoid some errors, particularly in column produced to a tight deadline. Many years ago I stressed that I regard Technical Topics as forum for new ideas, not all of which are likely to prove repeatable or even strictly accurate No guarantees can be given on experimental ideas still under development! I welcome comments from sceptical readers or those spotting printing errors etc. Fortunately, there is good evidence that the vast majority of 7T items do work as intended, and often provide useful additions to amateur lore! ==================================================================================
Intermodulation properties of switching diodes, by Dr. Ing. Jochen Jirmann, DB1NV
ZL4AI was contacted by a neighbouring ham, (known for many years). Peter Johnson ZL4LV. peter.Johnson@Paradise.Net.Nz Peter designed and developed from scratch in the early 1970s an HF transceiver. (Actually it is still under development and may soon have BA479s installed.) The local Branch of the New Zealand Amateur Radio Transmitters Association under Peters guidance sold this as a kitset. Peters design was the first use of diodes for band switching. Peter published this technique in English Radio magazines the early 1970s and thereafter the first commercial transceivers appeared with diodes switching bands. As the inventor of the concept Peter has collected articles on diode switches, and provided the following.

Page 68 of 151

Page 69 of 151

Page 70 of 151

Page 71 of 151

Page 72 of 151

Page 73 of 151

Page 74 of 151

Page 75 of 151

===========================================================================
-----Original Message-----

Page 83 of 151

From: thomas hohlfeld [mailto:thomas_hohlfeld@hotmail.com] Sent: Wednesday, 27 April 2005 10:42 a.m. To: jaking@es.co.nz Subject: RE: ts-940 Hi Jeff, thank you for your reply and congrats for the informative web site. I read about the PIN diode mod in a web message. I replaced diodes D9 through D20 of the RF board by the PIN types BA479. I did not replace D3-D8 because these switch a frequency too low for the BA478 to be an effective PIN. I checked the BA478 and found them to be good at frequencies above 2 to 3 MHz. The BA479 have been offered in different versions and it is important to use those which are designed for HF (not VHF). Certainly, other PIN diodes may also be useful. The IMD of my 940 improved by about 5 dBm after this mod. For re-alignment of the receiver, I mainly followed the instructions of the service manual for the RF and IF amplifier stages (I did not align oscillator and PLL circuits). I have a sweep generator (Rohde & Schwarz SWOB 5 equipped with log amplifier), which was very helpful to optimise the bandpass filters on the RF board. I established RX sensitivity with a HP8640B RF generator together with a home made audio voltage detector to determine an audio increase by 10 dB. I have two of the HP8640B, so that I am able to determine receiver IMD. The HP8640B are quite famous, since they produce a very clean RF signal and are sold at a reasonable price. By the way, I own two TS940 and use one of them for experimental modifications which are more critical, so that I would not really recommend others to reproduce them. If you are interested anyway, I will report on that later. Its past midnight now. 73 for today, Thomas >From: "Jeff King" <jaking@es.co.nz> >Reply-To: <jaking@es.co.nz> >To: <thomas_hohlfeld@hotmail.com> >Subject: RE: [ts-940] Re: Why don't more people use this group? >Date: Mon, 25 Apr 2005 09:09:42 +1200 > >Thomas > >I found your review of the FETS most interesting. >My reason for writing is to ask you to tell me more about the pin diode modifications you have undertaken. >Where are these diodes and what do you do to replace them? >What else did you do to realign receive? >How did you establish the 0.15 uV sensitivity.? > >Yours sincerely >Jeff King ZL4AI

Page 88 of 151

Page 89 of 151
Part #2 of my measurements will follow, where I studied the diodes behind the input filters (D4,6,8.20 and D21) which are run at a lower forward current. The measurements are already finished but the figures need to be arranged. Good luck for today! Thomas DF5KF
-----Original Message----From: thomas hohlfeld [mailto:thomas_hohlfeld@hotmail.com] Sent: Monday, 13 June 2005 4:31 a.m. To: jaking@es.co.nz Cc: hohlfeld@uni-duesseldorf.de Subject: TS-940S - pin diode part#2 and some other considerations Hi Jeff, here comes part #2 of the pin diode measurements, which concentrates on the diodes between the bandpass and the preamplifier of the TS-940. First a short comment on the 940s front-end: when the RF has passed the RX bandpass, three diodes follow before the signal reaches the preamplifier Q10. Of these, two are switching diodes (one of D6,8. D20, D21), while one (D26) is a pin diode. Only the two switching diodes are candidates for replacement. For test purposes, I assumed that D26 is fully open and D23 closed (AGC at highest sensitivity). In this case, we deal with two switching diodes in series. They are also in series with respect to their forward current, which is determined by R31. I measured 17 mA in my TS-940. The impedance, which these diodes see, is also important. I estimate it about 50 Ohm, because the bandpass filters of the TS-940 are constructed symmetrically. Therefore, my test setup was similar as before with the following changes: (1) I tested two diodes in series, (2) I used a forward current of 17mA and (3) I also measured at 10.1 MHz. Because the 1N4148 was so poor in part#1, I did not consider it further. The attached jpg file again contains a plot of the test setup. Here are the results (see attached jpg file): At 10.1 MHz (figs 1-3), the original Kenwood switching diode (1S2588) is as good as the pin diode BA479. The same also applies to higher frequencies, which I do not show here. The insertion loss of the two BA479 in series is slightly higher than that of two Kenwood diodes, but is still less than 1 dB (more on this below). At 7 MHz (figs 4-6), the 3rd order products are clearly increased by the Kenwood diodes (fig 5) in comparison with the reference (diodes shorted, fig 4). The BA479 (fig 6) is clearly better than the Kenwood diode, although a minimal increase is also seen compared with the reference. At 3.5 MHz the Kenwood diodes generate a lot of intermodulation products (fig 8) and the BA479 (fig 9) is obviously superior. The same is true for the 1.75 MHz band (figs 10-12). In summary, the BA479 is better than the original Kenwood switching diode at 7MHz and the lower bands at a forward current of 17mA. There is no relevant difference at 10 MHz and higher. It would also be interesting to know how the diodes behave at frequencies below 1.75 MHz. Unfortunately, my combiner is not appropriate for a lower

CONTROL BOARD

VOLTAGE REGULATOR HEATS UP AND CAUSES A SHIFT IN BFO ON IF BOARD
-----Original Message----From: thomas hohlfeld [mailto:thomas_hohlfeld@hotmail.com] Sent: Monday, 2 May 2005 9:23 a.m. To: jaking@es.co.nz Subject: RE: ts-940 (4) One of the voltage regulators on the control board warms up the bottom of the 940, which causes a small but detectable shift of the BFO on the IF board. I removed this regulator from the control board and mounted it on the big aluminium heat sink at the rear side of the TRX. Best 73s for today, Jeff Thomas, DF5KF
>From: "Jeff King" <jaking@es.co.nz> >Reply-To: <jaking@es.co.nz> >To: "'thomas hohlfeld'" <thomas_hohlfeld@hotmail.com> >Subject: RE: ts-940
>Date: Fri, 27 May 2005 19:35:16 +1200
Your mod (4) is also very helpful for me. I have heard about a TS-940 that is supposed to have this problem of frequency drift after operating for 30 minutes. It apparently shifts frequency slightly then jumps back. Just sometimes: comes and goes. Sounds like you have solved the problem. Wow thanks. Can you please tell me which regulator was it that you shifted to the heat sink? >Your sincerely >Jeff King

Page 102 of 151

From: thomas hohlfeld [mailto:thomas_hohlfeld@hotmail.com] Sent: Tuesday, 31 May 2005 9:15 a.m. To: jaking@es.co.nz Subject: BA479 etc. You also asked for the IC that warms up (my mod 4). I believe it was either IC7 or IC6 on the control board, but I am not entirely sure. Next time I open my 940 I will see and let you know. Warming up of the IC caused a slow shift of the 100 kHz BFO (L19). Indeed, L19 was quite sensitive to changes in temperature in my 940. Perhaps you should verify with a counter that the jumps in frequency you mention are really caused by this BFO. Best regards for today and vy 73, Thomas, DF5KF
-----Original Message----From: thomas hohlfeld [mailto:thomas_hohlfeld@hotmail.com] Sent: Friday, 10 June 2005 8:56 a.m. To: jaking@es.co.nz Subject: RE: BA479 etc. As my TS940 is open now, I had a look which of the voltage regulator IC I had moved back to the heat sink. It is IC7 on the control board, next to relay RL2. I include an additional jpg file which shows (upper figure) the place on the control board where I replaced IC7 by a connector with the three cables leaving (arrow). The lower figure shows the voltage regulator at its new place (arrow). The heat sink needed to be unscrewed in order to drill a hole for mounting IC7. I mounted IC7 isolated from ground. If you decide to do this mod, be very (!) careful not to make any mistakes. The primary 22V line may cause severe damage when connected to the 15V regulator output.

VERIFY THERMISTOR 101 IS ATTACHED AND FUNCTIONING
ZL4AI 940 had a very hot TS-940 power supply. On removing the power supply heat sink the thermistor 101 actually fell out of its housing metal housing. It had become unglued. It had been sitting in the correct position but probably was not making adequate contact thermal heat transfer. Hence not turning on the cooling fan. To verify the thermistor changed resistance I connected a ohm meter and heated the thermistor with soldering iron. It went from approx 16,700 ohms at 12 degrees C to 220 ohms at say 400 degrees C. I have no idea if these are correct resistance values but they give an indication of what happened. If anyone has the temperature table for Thermistor 101, please send to jaking@es.co.nz.

Page 111 of 151

On page 8 of the promotional brochure above, its shows that the heat sink should run at or below 40 degrees Celsius.

REPLACE Q101 AND Q 102

ZL4AI found after replacing the original power supply transistors 2n5885 (60 volt version) with the 2n5886 (80 volt version), the heat sink temperature seemed to decrease.
MOTOR BEARINGS GUMMED UP: TEMPORARY FIX
-----Original Message----From: kenwood-bounces@mailman.qth.net [mailto:kenwood-bounces@mailman.qth.net] On Behalf Of Garey Barrell Sent: Friday, 28 October 2005 4:48 a.m. To: Bill Stewart Cc: kenwood@mailman.qth.net Subject: Re: [Kenwood] TS-940S Cooling Fan Problem Bill Stewart wrote: >I have a TS-940S, s/n 6040XXX, which has a sluggish cooling fan (on left, facing front, behind the power trans.). Sometimes it will not start. I have shot WD-40 in it and tried to get oil to go down the shaft but sometimes it still won't start and if it does start, it turns slowly & erratically. I measured the voltage to be around 18VDC with the fan disconnected and connected, a fluctuating.5 to 1.5VDC with the erratic rotation. >Questions: 1. Is this no-load to load voltage drop normal? > 2. Does the voltage and fan speed increase with temp. rise? > 3. If the above is a problem, are there any mods. to replace this fan or maybe make the fan run all the time? >The fan runs ok if it gets beyond the low start-up point (on a seperate DC supply). >Any comments will be appreciated, thanks.Bill K4JYS Bill The problem is that the motor is drawing too much current at start-up. The supply voltage is applied through a series resistor and the excess current drawn because of the gummed up bearings is high enough to drop the supply voltage too low to start. The correct fix is to replace the motor. East Coast Parts has them but they are expensive, ~$30. You might be able to find a hobby motor that will fit, if you look long enough. A "temporary" fix is to put an 18V Zener diode across the motor dropping resistor so that if the voltage

Page 120 of 151

Ham To Ham #13 - October 1996 73's Ham To Ham column c/o Dave Miller, NZ9E 7462 Lawler Avenue Niles, IL 60714-3108 Lighten up From George Vaughn WA4VWR comes this tip: "I've found a local source for the bulbs that illuminate the Kenwood TS-940's sub-display. When one of them went bad in my TS-940S, I removed both and measured the voltage applied to and the current drawn by the single working bulb.12 volts at 75 milliamperes. A trip to the local Radio Shack (reg. trade mark) store resulted in my discovering standard RS replacement bulbs of the exact size and shape (RS Cat. #272-1092), but the RS bulbs draw 15mA less, or 60mA - and they lack the little green "bootie" that the original Kenwood bulbs have. The green "bootie" can be carefully removed from the old bulb, provided it hasn't been "cooked" into place too badly, and with the aid of a touch of clear silicone grease, can be installed on the RS replacement bulb quite easily. The 15 milliamp difference in current (and light output) is about the same as if one were to put a 47 ohm, 1/2 watt "bulb-life-extender-resistor" in series with the Kenwood bulb, so to me it's perfectly acceptable. The biggest difference is in the price.$1.49 for two of the RS bulbs vs. $4.19 each ($8.38 total) plus $6.00 shipping, for the Kenwood relacements. That's $7.19 per bulb from Kenwood.75 cents per bulb from Radio Shack. Guess which ones I'm using in the future. What about the TS-940S's 'S-meter' bulbs.does Radio Shack carry a replacement for them? Yes, but this time the difference is more pronounced. The bulbs in the S-meter are 12V at 75mA; the Radio Shack replacement with wire leads (Cat. #272-1141) is rated at 12V but this time at only 25mA. It's noticably dimmer than the stock Kenwood bulb, but it may be acceptable to many; you'd have to try it and see. Personally, I chose to use Radio Shack's Cat. # 272-1143, a 12V, 75mA bulb, but with a screwin type of base. If you use the same bulb as I did, it's advisable that you not solder the 12 volt feed wire directly to the screw-type base, but rather wrap a couple of turns of non-stranded, fairly stiff wire around the screw-threads instead. Also be sure to connect the "ground" 12 volt feed wire to the screw-base, not the "hot" wire. If the screw-base on this bulb were to ever cut through the insulating grommet, you might damage your set if the hot 12 volt lead were connected to it and then shorted the supply bus to ground. You can easily determine which feed wire is "hot" and which is ground by measuring each with a voltmeter when the set is turned on. The "hot" wire will have 12 volts on it, and of course the ground wire won't. Again, make sure that the ground wire connects to the screw-base shell of the replacement bulb. The tip of the replacement bulb should be reasonably safe to solder the "hot" 12 volt lead to, using the existing "solder-blob" as a connection point.do it quickly. One other small caveat, the #272-1143 bulb is just a tad too large to fit into the existing holes in the back of the TS-940S's meter, but a few seconds with a tapered reamer resulted in the right hole size for a nice fit.take your time and don't get carried away! If done properly, the original Kenwood bulbs can still be used later on if desired. By the way, it is necessary to remove the metal meter mounting bracket to perform this particular step, but again, the cost savings are well worth the small extra effort."

Page 121 of 151

Moderator's note: We've all noticed how difficult it's become to change the pilot lamps inside of most of today's radios? In the old days - when radios and lamps both were a lot bigger - changing a pilot lamp was a pretty straight-foreword, easily accomplished job. The lamps were always mounted in sockets, and usually just a twist of the wrist popped it right out, ready to receive a new one. Not so today.most are now on small wires, soldered in-place and buried deep within the wiring of it's front panel. It usually requires some internal "surgery", so many hams either don't bother changing them at all when they burn out, or they leave the job for when the set has to be disassembled for some other troubleshooting reason. George has offered some well-thought-out advise in his tips from above; here's some more for you to consider. What follows won't make the task of bulb changing any easier, but it just might double or triple the time between pilot lamp failures. When a lamp does burn out, many probably think first of going back to the manufacturer for a replacement. There's nothing wrong with that idea, especially if it's a very specialized type of bulb. But as George pointed out, it's probably the most expensive and time consuming route to take, especially when there may be a much more cost effective approach. Since Radio Shack stores stock a number of small low voltage lamps, many of which will either fit directly or can be adapted to fit, a bit of "ham innovation" is sometimes needed, as displayed in George's piece. Take a look into what Radio Shack calls their 12V micro-lamp, Cat. #272-1092. It may well work as a replacement bulb for LCD displays and other situations where a very small size lamp is in order. Hobby stores also carry what they call "grain-of-wheat" lamps, which are very similar, but be sure to ask about their voltage and current ratings. By the way, using a lamp rated at a higher voltage is fine, as long as it will provide enough brightness once it's installed; in fact, it will last a lot longer than one rated at the nominal voltage. Additionally, if you lower the voltage to a 12V lamp, even by just a couple of volts, you'll increase it's life dramatically. I've seen test curves that prove that the life expectancy of a lamp zooms upward as the voltage across it goes down, and vice versa of course. Putting a resistor in series with each lamp that you replace, will often give you two to three times the life expectency from a given bulb, everything else being equal. There are three things to consider before doing this: 1) what value resistor will be needed, 2) what its wattage rating should be and 3) how much loss of light is acceptable? Lowering the voltage to the lamp will decrease its brightness - and shift its color toward the red region - so you'll have to visually judge whether you can accept both of these consequences. You can install the lamp, clip-leading a resistor in series with it, then looking at the meter or display under normal room lighting, to see if it's okay for you own particular situation. To arrive at the right resistor values, simply use Ohm's Law, plugging in the correct numbers for your own transceiver's lamp supply: Voltage drop desired divided by the lamp's rated current equals the resistance needed. and Voltage drop desired times the lamp's rated current equals the resistor's wattage. By way of an example, let's take the Radio Shack #272-1092 lamp that I mentioned before, which has a current rating of 60 mA or.06 Amp. Let's say we'd like to drop the 12 volts feeding the lamp down to 10 volts, or a 2 volt total drop. We plug in the numbers: 2 (volts) divided by.06 (amp) equals 33 ohms and 2 (volts) times.06 (amp) equals.12 watt Now we know that we'll need a 33 ohm, 1/4 to 1/2 watt resistor in series with each lamp in order to drop the 12 volt lamp supply down to 10 volts. A 1/2 watt resistor will provide a 4 times safety margin for heat dissipation (dissipation ratings for resistors generally assume their full lead length, in free air, so it's

ZL4AI adds: from page 78 / 79 of the TS-930 service manual, confirms the above: Japanese SG 0dB = American 0.5uV from page 51 of TS-940 Operating Manual If a standard signal generator ( SSG) is available, adjust VR-4 so the S meter indicatesS-9, at 14.175MHz for a 40 dB (50uV) signal from page 69 of the TS-930 service manual

Page 129 of 151

SSG output: at 14.175MHz 100dB /u: = S meter reading S9+60dB +- 6dB This 100 dB/u S-meter maximum calibration information seems to be unclearly laid out in the TS 940 service manual, but is inferred in the accompanying notes in the TS 940 service manual. It looks like Kenwoods made a typo and missed it out.
The TS-940 Service manual on pages 72-73 is not very easy to understand: ZL4AI have prepared the extended service instructions: Measurement Item 6.1 S meter Condition BAND: 14.175MHz SSG output : 14.175 MHz 0dB/u SSG output: 8dB /u AGC: FAST SSG output: 40dB /u SSG output: 100dB /u

Test equipment

Adjustment Terminal Unit IF Part VR3 Method Adjust meter nee for mechanical f Set the VR1 to CCW ADJ to S1 ADJ to S9 Verify full scale Repeat ADJ S1 a S9

SSG AF V.M SP SCOPE

RF 6.2 S meter 6.3 6.4 6.5 Red are items Kenwood missed out IF IF

VR1 VR1 VR4

dBm values quite interesting to compare with other expert observations, tahts S Meters are not linear: To: <amps@contesting.com> Subject: [AMPS] s meter calibration From: w7iuv@nis4u.com (Larry Molitor) Date: Tue, 13 Jun 2000 22:57:40 +0100 At 07:45 AM 6/13/00 +0100, Ian White, G3SEK wrote: >According to the lab reviews in the magazines, most modern receivers seem to be calibrated so that the difference between S9 and S9+20 is pretty close to 20dB. Below S9, the scale looks linear but the dB per S- point is not1 It typically takes many more dB to get from S2 to S3 than it does to get from S8 to S0 - often less than 3dB per S-point at the top end. >It doesn't have to be that way - there are engineering solutions that could easily deliver the full IARU specification - but when everybody on HF is "five nine" anyway, who cares any more?

Page 130 of 151

> >73 from Ian G3SEK Ian and all, As has been said before, the manufacturers correctly assume that the majority of buyers are technical idiots. Have a S-meter that has 1 dB per S-unit and about 5 uV for S 9 is a good marketing thing. Besides it's a lot cheaper to build. I would hope that anyone who actually cares about such things would take the time to "calibrate" the meter on their store-bought radio. Since I do this with all my radios, I would not care to pay extra for a manufacture to make a feeble attempt at a real meter. Using a HP8648C generator (at 14.1 MHz) this last time, I produced the following chart for my FT1000D: S1 = -103.5 dBm S2 = -101.5 dBm S3 = -98 dBm S4 = -94 dBm S5 = -90 dBm S6 = -85 dBm S7 = -80 dBm S8 = -75 dBm S9 = -70 dBm +10 = -60 dBm +20 = -51 dBm +30 = -42 dBm +40 = -33 dBm +50 = -24 dBm As you can see, it's kinda poor at the bottom end, but quickly stabilizes at about 5 dB per S-unit. With S-9 being within 3 dB of 50 microvolts and 5 dB per S-unit, this particular FT1000D has the best Smeter out of the 10 or so radios I've checked. With a chart like this handy, it gives you a real good idea just how good the other guys antenna is or how much gain his amp really has. While the guy on the other end is usually an idiot and won't believe what you tell him, at least you will know for sure. Since it's so easy to do this, I'm surprised there aren't more folks with handy little charts for their radios. I know, not everyone has a room full of good test equipment. But I bet most people on this list know someone who does or has access to it one way or another. Give it a whirl, you might be amazed! 73, Larry - W7IUV

Page 139 of 151

OF THE NEWER ONES, SO THAT AIN'T THE PROBLEM) Also by changing about 45 diodes over to PIN's there is a dramatic performance improvement in RX performance. I also use cascaded IRCI filters for both CW and SSB.the Kenwoods have poor skirt rejection. I have 4 940's here that are used fm HF thru microwaves as platforms for transverters. I quickly sold a FT1000D as not worth the money that 2 well modified 940's could perform at. I had a TS870 here on loan.it has a great RX but very prone to overload on 40 thru 160. GL and 73 Carl KM1H 261 DXCC on 160; 309 on 80 ---------------------------------------------------------------------(Comments from George Guerin.K8GG) 1. My experience with the TS-940 is it does not hear as well as the TS-930 or TS-950SDX. Also there is generally a spike on the leading edge of the first CW character sent which risks grid damage to tubes like the 8877, 8874, 3CX800A7, etc. 2. Your description of the TS-570 sounds very good. Maybe they will make a TS-970 soon?? 3. I hear there are problems with the TS-870, because there are no filters at all, except digital in the last IF. This creates birdies in the pass band, since it is at something like 14 or 17 Khz, and a signal 28 or 34 Khz away can leak through. I hear one W6 added filters and cleaned the birdies, but Kenwood will not do this on production units, so we will have to wait for a TS-871 or 880? 4. I have used the FT1000MP and it does a pretty good job, but I haven't put it side by side with other radios. Setting the two DSP controls on the concentric rotary switches is a bit tricky. The dual receive and or split is very good and easy. A friend in Chicago says it hears better on CW than the FT1000D and the TS950SDX. On phone I like the TS950SDX best, but that is not true 160 operation. 5. I would like to try the IC-775. More money, but the automatic carrier null is very fine. On CW, I would like to try one on 160 for a while myself, and see about the noise removal system. 6. I understand TenTec has a Omni 6+ just out with dsp. I have no way of trying it and the TenTec "chemistry" and my body chemistry do not get along, so I will never buy one. I do have friends on 160 with Omni 5 and Omni 6 radios doing well. They do have good beverages. One has a directional vertical array!! I do have a TenTec tuner I like a lot. There is no chemistry problem without electronics inside the box! HI ! George Guerin ------------------------------------------------------------------[NE3H compares the 940 to the Omni VI (not the VI+)] On the OMNI. no question, best receiver that I've ever heard. Yes, I think the FULL DSP receivers may be more sensitive. or have lower noise floor. but none of the HAM gear that I am aware of. I cannot hear the diff between my old 940 and the OMNI. if normal ambient noise, most people cannot hear the diff. The outstanding characteristic. and the second reason I got TWO OMNIs. is that you can have an S9 + 20 signal next door to one in the mud. and it does not make a difference. I have a neighbor. a mile away. who runs a kW on RTTY. ( as do I ) and we can op within a Khz or two without disturbing each other. Fact is, if you have lots of line noise. I don't think you'll notice the diff in rcvr sensitivity. The noise

Page 142 of 151

Very little SSB testing, but the heterodyne filter works as good (or better) than the one on the 59+ DSP. Did not have multiple heterodynes to see how it works, but would guess OK. Forgot to check for transverter input!!! Dope! Suppose that auxiliary receive antenna is possible somehow. COMPARISON OF TS940 TO YAESU 1000MP: I borrowed K9IG's 1000MP for similar testing. I felt like I should sign away rights to my firstborn grandchild if I damaged it, so better believe I was REAL careful with it and read the manual first!! But Greg seemed unconcerned that I was driving away with HIS 2500 dollar radio in my truck. I set up similar to the TS570 test, and as luck would have it the power company chose to temporarily fix the line noise (after five months!!!) that day. With all the mechanical and DSP features kicked in (including a DSP59+ on the 940), the TS940 and the FT1000MP performed about the same on 160 through the other bands (CW only tests). Some of the controls WERE tricky, and the preset filters on the 1000MP took some getting used to. There must be about two million bells and whistles on the 1000MP, and my fat fingers found a few by accident. It is an impressive rig. but without line noise, not enough to make me dump the old 940. Without the noise reduction, the 940 is OK. One thing I noted. small point. S meter readings were comparable for both rigs at low signals and noise levels. but S meter readings were higher on the 940 for stronger signals. of course, that does not mean much, as an S meter ain't that accurate. just needed more attenuation with 940. I packed up the 1000MP and got it ready to take back to Greg (about 8 miles from me). then Indianapolis Power and Light came through just in time!!! Line noise returned, but only at S9 levels. I quickly patched the 1000MP back into the setup and compared reception. In this case (with strong line noise), the 1000MP was better at pulling weaker signals up out of the crud. Even with noise blanker on, the 940 lost some of its ears. Noise blankers on both rigs eliminated the noise HEARD, but the 1000MP was better at finding signals and bringing them up than the 940 with DSP59+ was. 4/15: Bill Tippett reports that his 1000MP is extremely clean (no intermod products observed) compared to the TS930 he retired. COMPARISON WITH OMNI VI+ I wanted to test an Omni VI+, but none to be borrowed locally, so I asked NE3H for his opinion (see above). In the meantime, power company has repaired a number of defective lightning arresters, a bad transformer, and God knows what else to the point where my line noise is now S3 or less most of the time.so the 940 gets a reprieve. I fact, even though it's almost too late in the season, am working DX on 160 most evenings now when I could not hear it in winter!!! With a little luck I might hit 50 countries for the 96-97 season. I wish I could find the mail messages I sent to George because there was more specific info in them. but this report is the bottom line. From my own observation, the 1000MP and the TS570 outperform the TS940 receiver with high line noise levels. Mechanical filters are needed on both rigs. But with little line noise the 940 is still pretty dang good. Thanks to K9IG (formerly KO9Y) and N9QCT for the loan of their rigs. Mel KJ9C