PART II - Introduction to the Tektronix 2215 Analog Oscilloscope Overview:
An oscilloscope is an electronic measuring device which provides a two-dimensional visual representation of a signal. Because the oscilloscope allows the user to see the signal(s), their characteristics can be easily measured and observed. The oscilloscope displays a graph of voltage (on the vertical axis) versus time (on the horizontal axis). Most electrical circuits can be easily connected to the oscilloscope typically with probes. x There are four major control groups on the Tektronix oscilloscope: (1) the Display group; (2)the Vertical group; (3) the Horizontal group; and (4) the Trigger group. See Figure 5, below.

TEKTRONIX 2225

VERTICAL TRACE SEP INTENSITY POSITION POSITION
HORIZONTAL TRIGGER COURSE FINE LEVEL
NORM INVERT ADD ALT CHOP BEAM FIND CH! BOTH CH1

1X ALT MAG

MODE HOLDOFF

CH1 VOLTS/DIV FOCUS

CH2 VOLTS/DIV

SEC/DIV SOURCE COUPLING

POWER AC GND DC CH1 AC GND DC CH2 5X 10X 50X EXT
Figure 5: Front Panel of Analog Oscilloscope

Display Group

This group is used to display and adjust the signal for optimal viewing. It consists of the display screen, the intensity-control knob, the beam-find button, the focus-control knob, and the power switch. x The display screen is laid out in a 8 by 10 centimeter grid. The oscilloscope draws a trace or graph by moving an electron beam across the phosphor coating on the inside of the cathode-ray tube (CRT). The excited phosphorous glows for a short period of time, thereby tracing the path of the beam. The intensity-control knob is used to adjust the brightness of the trace. The level should be set to the user's preference; however, increasing the intensity beyond a certain point
Oscilloscope Lab - Rev February 2004
will make the trace "fuzzy." The intensity level should never be increased past the point where the trace has sharply defined edges. x The beam-find button allows the user to locate the electron beam anytime it's off-screen. Push the beam find button to temporarily reduce the vertical and horizontal deflection voltages so that the beam always appears within the 8 by 10 centimeter screen. The focus-control knob adjusts the electron beam for optimal trace resolution.

Vertical Group:

This group is used to adjust the vertical components (Y-axis) and the vertical position of the signal. This group consists of the vertical-position knobs, channel-selector switch, voltsper-division-selector knobs, input-coupling switch, the channel-mode-selector switch, the channel-2-invert switch, and the BNC connectors. Because the Tektronix 2225 oscilloscope is a two channel oscilloscope, there is one set of switches for each channel. x x x The vertical-position controls are used to vertically move the trace of one channel or the other. The channel-selector switch, labeled CH1/BOTH/CH2, selects which channels are displayed on the screen. The volts-per-division-selector knob sets the vertical scale for each channel's trace. 1. Since a 10X probe is used in this lab, all readings should be made from the 10X box on the knob. 2. Each channel can have a different vertical scale. 3. A division is one "block" on the screen. 4. Each tick mark is one-fifth (0.2) of a division. 5. This knob is marked in both volts and millivolts. x The input-coupling switch, labeled AC/GND/DC, selects the coupling mode of that channel's display. AC means that only the alternating portion of the signal is displayed. DC will display both the alternating portion of the signal, plus any DC component. GND shows the 0 V reference level. The trace-separation knob is used in conjunction with the horizontal-magnification controls, to be discussed later. The channel-mode-selector switch, labeled ADD/ALT/CHOP, is activated only when BOTH is selected on the channel-selector switch. ADD graphically adds the Channel 1 signal to the Channel 2 signal. If the channel-2-invert switch (NORMAL/INVERT) is set to INVERT, then ADD will in fact subtract the Channel 2 signal from the Channel 1 signal. ALT traces one channel, then the next. CHOP works like ALT, but jumps back and forth between the two channels during a single trace.

Horizontal Control Group:
The Horizontal Control Group consists of the coarse and fine position knobs, the horizontal-magnification switch, the seconds-per-division-selector knob, and the magnification-scale-selector switch. x The coarse and fine-position-knobs allow the horizontal movement of the traces in a rough manner and in a precise manner, respectively. These are used to position the traces in a manner that makes measurement both more convenient and more precise.
The horizontal-magnification switch (X1/ALT/MAG) selects the regular (X1) and/or a horizontally magnified trace. 1. The trace separation knob in the Vertical-Control Group allows for the vertical separation of the X1 trace from the magnified trace when ALT is selected. 2. If ALT or MAG is selected, then the magnification-scale-selector switch (5X/10X/50X) is activated. x The seconds-per-division knob sets the time base (horizontal) scale. It is marked in seconds, milliseconds, and microseconds. Note: There is only one horizontal scale for both channels.

Trigger Group

In order to display a signal, the oscilloscope must be able to lock onto that signal; the function of the triggering controls is to do just that. Triggering can be a complicated topic, and is beyond the scope of this lab. For more details, you are referred to the Tektronix manual. The trigger group is made up of the trigger level knob, the rising/falling edge switch, the trigger mode switch, the holdoff knob, the trigger source switches, and the trigger coupling switch. x The trigger-level knob sets the voltage level at which the oscilloscope will trigger. If a signal is running--that is, not stable--the trigger level may be too high or too low for the oscilloscope to recognize the signal. Often you can lock in a running signal by rotating this knob to the left and to the right. This adjustment provides a mechanism for ignoring small (low voltage) signals that are well below the level of the signal you are interested in. This knob is not indexed. The rising/falling-edge switch selects whether the oscilloscope will trigger on the positive (rising) or negative (falling) edge of the signal. The trigger-mode switch will normally be set to AUTO, but sometimes it is necessary to use NORM. Other settings are not relevant to this lab. The holdoff knob affects the delay associated with triggering. You should consult the manual if more information is desired.
The trigger-source switches select which signal the oscilloscope will attempt to lock onto. Possible choices include CH1, CH2, VERT MODE, or EXTERNAL. Selecting CH1 or CH2 will make the oscilloscope attempt to trigger on those channels. If no input is available on that channel, there may be problems when attempting to view both channels simultaneously. For this reason, it is recommended that this switch be left on VERT MODE, which provides an automatic trigger on either CH1 or CH2. The trigger-coupling switch is another more complicated feature which will not be discussed here. This switch should typically be set to AC.

How To Make Readings on the Oscilloscope:
x Peak-to-Peak Voltage: Use the vertical-position knob to place a peak (positive or negative) on a horizontal line, keeping the peak on the screen. Use the horizontal-position knob to set the next (opposite sign) peak on the center vertical line. Count the number of divisions between the positive and negative peaks. Note: The divisions are further subdivided into 1/5 (0.2) by the tick marks. Multiply the number of divisions from step 3 by the volts/div setting for the channel in use. x Period: Use the horizontal-position knobs to align any edge of the signal with a vertical line. Use the vertical-position knob to place the next identical edge crossing on the X-axis. Count the number of divisions along the horizontal line to the next crossing in the same direction. Multiply the number of divisions from step 3 by the sec/div setting. Note: The divisions are subdivided into fifths (0.2) by the tick marks. x Frequency: Measure the period of the signal (T). Calculate frequency (f) using f = 1 / T.
Figure 6: Measuring a Signal.
Example: Assuming the Volts/Div knob reads 2 V/div, the above peak-to-peak voltage would be: Vpp = 2 volts/div * 5.2 div = 10.4 volts Assuming the Sec/Div control knob read 50ms, the above period would be: T = 50 milliseconds/div * 5.25 div = 262.50 milliseconds = 0.2625 seconds

An Ongoing Refurb Log

Don Lancaster Synergetics, Box 809, Thatcher, AZ 85552 copyright c2004 as GuruGram #34 http://www.tinaja.com don@tinaja.com (928) 428-4073
F or years, Ive been meaning to put together a collection of tips and techniques
involving my insider refurb secrets for electronic test equipment and similar tech and not-so-tech items that we offer on eBay. A continuing Thoughts on Refurb and an expansion of Degubbing Secrets. Im not sure exactly where we are going with this just yet, but well sort of keep it in a "blog" format except that the newest stuff will normally be last to simplify and stabilize our layout.
Tektronix 2213 and 2215 Oscilloscopes
These were among the finest analog scopes of all time and are an ideal classic instrument for student, home, or light lab use. They are still fairly easy to find at community college auctions and still ( when properly presented ) can command around $160 bare or $240 with all the probes, docs, and accessories on eBay. The usual problem is a stuck on-off switch. Except for one tiny detail, this is easily cured with a pffft of Radio Shack TV Tuner Cleaner and cycling the switch a few hundred times. The infuriating detail is that the switch is inside the high voltage cage and that the cage lower left rear 4-40 Torx T-8 flathead screw is almost always frozen. Try drilling most of the screw out with a #30 drill and then briefly reversing. Be careful to stay centered on the steel screw and not wander off into the softer aluminum case. An alternative that does take some practice: Try "snorkeling" the TV tuner cleaner tubing through one of the lower left vent holes. Entering from behind the rear panel. A high intensity lamp shining through the top vents can help bunches. This may let you avoid removing the high voltage cage entirely. The 2213 and 2215 are easily serviced. To open the case, remove two Torx T-10 screws on the back plastic endpiece and one from the case side. Torx screwdrivers are readily available just about anywhere these days.

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NEVER attempt to service Tektronix ( or any similar gear ) without all the necessary Torx screwdrivers or bits!
There is a crucial difference between tuner cleaner and electronic spray solvents.
TV Tuner cleaner intentionally leaves a mineral oil residue. Electronic spray solvents do not. But may attack plastics.
A second chronic early 2213/2215 problem is that the switchmode power inductor may work a little loose with age and can create an up-the-wall annoying audio whine. These are very early production that used a triac preregulator. They often can be identified by a fixed rather than a removable line cord. Ive tried all sorts of silicon rubber glopping and neoprene washer isolation stunts, but none seem to work well for me. Others seem to feel there is no good solution. Other than avoiding any fixed line cord 2213 or 2215s. Please email me if you have a workaround here. CRTs in the -A versions are slightly different than the originals in that they have an integral high voltage connector. They apparently can be substituted with minor and obvious rewiring. A thorough cleaning is all that most of these scopes will need. If knobs are loose, check for Allen screws when present and tighten them if needed. An.050 Allen Wrench might be required. These might be hard to find except in sets. Note that SAE and metric Allen wrenches are not interchangeable. A quick and dirty checkout on any oscilloscope can be done by first getting any trace at all on the screen, then adjusting focus and brightness for a bright fine horizontal line. Next check the horizontal sweep time for smooth operation and no missing steps. Going everywhere from a full line to a spot moving slowly from right to left. Start with line or auto sync. Switch to channel 1 and a fairly sensitive setting. Then touch the input connector with a screwdriver whose blade you are touching. Observe a sixty cycle hum display on the screen. Check the attenuator switch for changing display sizes. Then repeat for channel 2. Finally, go to normal triggering and verify a trace only when you touch the input. Be sure you are on the main sweep when you do so. If any of these tests fail, recheck all your switch settings and try again. On other instruments, be sure there are no hidden or rear switches that can cause grief. An important rule

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Never attempt to go beyond simple refurb without having all of the needed service manuals on hand!
It is often possible to use eBay as a "lending library" to pick up service docs. If the repairable item is oddball enough, you can later resell the manuals. Sometimes for even more than you paid for them. Docs can also be found via Google. Online Tek help includes a very active Yahoo TekScopes user group. Plus the usual sci.electronics.repair and sci.electronics.design newsgroups. Other useful Tektronix resources include Stan Griffiths and Dean Kidd. "Tektronix Blue" paint is available from Stan. But Ive found that most retouch attempts on anything end up looking awful. Note that Tektronix recently released all of their earlier tech docs to the public domain. You can now legally copy and redistribute their early manual info. "Early" apparently being anything they are not currently selling.

Dimpling Your Own Chad

It always pays to look around for ultra low cost quantity buys of strange stuff. So long as you avoid this trap
Never overvalue something just because you know nothing about it! Or wrongly assume others will have any interest.
Our local county yard had a recent auction where bunches of old voting booths were offered. These turned out to be the "dimpled chad" Votomatics that were identical in make and model to the Florida ones that were the sole cause of the Iraqi war. And thus "should" see some strong demand as collectibles. But they were not without their problems. Some were partial, others cracked or broken, others with nonworking lights. But the biggest problem was age had made the plastic side privacy panels brittle. Many were broken and the rest were quite fragile. Especially the crucial case top supporting clips. I first sold a few of the very best of these following these usual eBay rules
Never sell anything you feel bad about. Always understate condition and value. Always try for a 21 day cashout. Defer refurb cost and time on unproven items. 34. 3
Basic refurb was done by combining the best of the better units. A pop riveter, large retaining ring pliers, and five minute epoxy were of great help here. Speaking of which
NEVER try to install or remove a retaining ring or snap ring without using the correct special pliers!
Thorough cleaning worked wonders. Fluorescent light problems were usually caused by missing, broken, or dead bulbs or starters. Most were easily swapped out. A few lights had cracked sockets. These did not seem worth fixing as enough functional units remained. On all but the finest booths, I decided the best route was to divide and conquer. The actual voting machine part was typically in excellent shape. These also store and display better and ship more cheaply. And should be highly collectible. Which brings about the obvious question: Who would gleefully buy a gutted voting booth with busted privacy panels? The not-so-obvious answer: Amateur

Astronomers!

Uh, lets restate that: Who would buy a low cost rugged high quality aluminum case that includes its own snap-together legs for use as a combined field data gathering desk and equipment stash? With optional ( but astronomically useless ) internal fluorescent lighting that was easily removable for extra space or weight. Long ago I found out that pen plotter motors were unsellable at any price but the identical laser lightshow galvos flew on outta here. The big message both then and now is
Always seek out possible non-obvious uses and obscure markets for what may be otherwise hard-to-sell items.

Reading IC Date Codes

Most integrated circuit manufacturers use a four digit date code of year-week format. Thus 9845 would be in the fall of 1998, while 0312 would be winter of 2003. Often these will be the lowest or last number to avoid confusion with the actual part number. Naturally, the assembled circuit board has to be newer than the newest of date codes present. Reading date codes can be a most handy tool to evaluate the obsolence and usefulness of many electronic items. In particular, a 1996 date code is unlikely to work with Windows 98 and is probably not plug and play.

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Salvaging Disasters
It always pays to carefully inspect what you are buying. Or at least view any available digital photos
The true costs in a "bargain" buy lie in the shipping, storage, your time, and how many of the items can be refurbed.
Back in the days when DRMO still did $50 deliveries, I took a chance on some unseen fuel transfer pumps. And got a great heaping pile of burned and rusted hulks for my effort. These were an incredibly stupid design that only the military could have dreamed up. They were apparently designed to transfer fuel from drums to vehicles or aircraft or whatever. Instead of an intelligent mod to a stock pump, these beasts tried coupling a premium grade pancake instrument motor to a conventional but high end hydraulic gear pump. The motors and pumps, of course, promptly froze under typical military use. Brush sparking wasnt all that great either. Once I got past the "oops" phase, I realized that
Useless items can sometimes be salvaged by splitting them in half and selling each half to wildly different users. Useless items can sometimes be salvaged by swapping the best parts from the worst items to the better ones. Useless items can sometimes be salvaged by having the buyer do their own refurb. Who may be better at this than you are.

So, farmers or ranchers always want to avoid buying a new $450 hydraulic PTO pump. And thered be all sorts of robotic and automation uses for refurbed $700 pancake servo motors. So long as you didnt do anything stupid with them such as coupling them to a hydraulic pump. In an explosive and corrosive atmosphere. The first problem was physically separating the beasts. The screws, of course, were all frozen. Most were removed by using the impact wrench at a nearby garage. You can also buy a "hammer style" impact wrench at any auto supply for under $10. The most obnoxious screws were dealt with by partially drilling them out and then using an EZ-out screw extractor. Penetrating oil works wonders. The pancake motors were completely disassembled into piles of rotors, front bells, rear bells, and brush assemblies. Damaged rotors were discarded or traded to artists for craft projects. The other rotors refurbed nicely with steel wool followed by household copper cleaner. Being extremely careful not to leave any steel wool fragments remaining.

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Most end bells cleaned up nicely with a little more steel wool work. Loose magnets were replaced with superglue, being careful to keep the N S N S N S pole orientations. And the brush assemblies were fixed by mixing and matching. The final units did not look all that bad and worked just fine. Nearly all of the hydraulic motors were also frozen. But also had exceptionally low hours on them. There were no signs of actual wear at all! The pumps were first soaked in gasoline to try and free them up. The one side plate was then removed if needed to try and clean up the gears. But I avoided messing with the easily damaged main shaft seal. After cleanup, these were given the usual -- heh heh heh -- Sherwin-Williams overhaul with glossy black paint. Being a standard major brand hydraulic part, rebuild kits were available for $19 each. But rather than mess with these, we simply guaranteed the units to not be frozen and told the buyers they might have to do their own rebuild. A typical user would test their unit and go ahead and use it as is if there wasnt oil spraying all over everywhere. Based on the premise of

Iffen it aint broke, dont fix it!
Buyers were overjoyed at paying $25 to $49 for a $450 pump that, at worst, they would have to add $19 and a little time to.

Finding Pinouts

On any strange older item with a mystery interface, the first thing to do is to try and contact the manufacturer. Sometimes simply guessing the company url will work. If not, start with Google or any of the other search engines on my home page. That good old Thomas Registry can also be of help. Followed by the usual backup resources of the sci.electronics.design and also the sci.electronics.repair newsgroups, and the old Deja News newsgroup searching service, which is now part of Google. Two lesser known methods to get pinout info are the Data Bookshelf and the WayBack Machine. Wayback is particularly useful to track name changes and who bought out who. Links to these and others are on my Home Page. Note that interface pinouts will do you no good if you cannot also determine ( or at least make a wild guess at ) the instruction set or command set needed to go over that interface. Lets look at two recent interface puzzles. The first involved an old DecTalk speech synthesizer. Visual inspection showed the input went to a mystery ic.

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A chip that turned out to be a variant of a stock transient protector. One with "straight thru" pinouts. But behind the mystery chip was a plain old Maxim RS232 chip. Thus, we had a serial data interface we could make a reasonable guess was at 1200 baud. Based on its age and intended use. While I could have played around with input combinations, I eventually found the pinouts on the web. And made sure the customer already knew how to interface the device. Our second example was a "moving sign" LED display. This one was an older unsupported orphan and worth $30 at best on eBay, so I just farmed it out to another eBay seller. But here is how I would have found the pinouts should the project have continued I first would have wrapped a 47K resistor around a scope probe so that I could simultaneously touch and view any given pin.
With TOUCH AND VIEW An UNCONNECTED pin appears as a large sinewave. A CMOS INPUT pin appears as a clipped sinewave. A GROUNDED pin appears as a solid, zero volt ground. A LOW OUTPUT pin will be NEAR but not at ground. A SUPPLY pin will be high and NOT drop if loaded. A HIGH OUTPUT will be high and WILL drop if loaded. A NEGATIVE pin is probably an RS232 signal line.
Make your first pass with the unit unpowered. This will separate unused pins from any ground or supply and active pins. Then apply power to find supply values, output states, and such. Special treatment may be needed for TTL inputs (try pulling them to zero with a 330 ohm resistor) or when higher power buffers or line drivers are in use. On an older LED scrolling display with a 20 pin DIP header, it may be reasonable to assume a parallel port interface over ribbon cable. And that the wire sequence would be port compatible in sequential order. From here, ASCII characters and control sequences could be applied to work out the exact interface and coding.

Thoughts on Pricing

There is nothing more disconcerting than placing an oddball electronic or medical item on eBay and having the item grabbed by Buy It Now nanoseconds after you posted it. Clearly, you should have charged a lot more.

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Ive found that it pays to purposely list any big ticket item once or twice with a much higher pricing than you expect to receive for them. What you are doing is betting a week or two of delay and $3 to $6 dollars worth of your lost filing fees against a $100 or higher additional return. More often than not, the bet pays off. Should you have items in large quantities, the opposite tactic may work: Open with a lower than desired price and then slide the price upward to continuously seek out the most you can get for the items consistent with selling all of them in a reasonable time period. Ive found a fifteen month sellout is often optimum. Much more on eBay selling strategy appears on our Auction Help page. Especially our eBay Secrets, Son of eBay Secrets, eBay Selling Strategies, our eBay Buying Stratgies, and eBay Photo Secrets files. Along with bunches of others.

A Refurb Summary

Heres a repeat of the guidelines I just placed in ENHEBAY2.pdf Make a determination as quickly as possible whether an item can be sold as is, as is with minor cleanup, needs minor repair, needs major rework, sellable as is, sellable for parts, mixed and matched with others in the group, stripped for parts, held for parts, or flushed outright. A dozen projects needing minor rework (tighten the screws, replace knobs, improve cosmetics) can be done in the time it takes to doing anything major to one item. And much more certainly. Always ask "What am I getting into?" Have your hired help do the routine stuff such as any initial cleanup and final out-the-door appearance upgrading. Spend your own time where it will do the most good; but delegate otherwise.
eBay can often be used as a lending library to get the repair and service manual for any higher ticket item that has a high probability of repair. Always try to have full tech info before attempting anything major in the way of repairs. Often the manual can be resold at a profit or as item added value.
It is super important to keep your refurb area clear! Ideally, a project should be handled only once. If absolutely necessary while waiting for parts, the item can be placed in a tote and tagged with required further action.

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Any item kept for ten weeks without completing refurb will most likely never be finished. Continually review all of these projects for downgrading and elimination. The earlier you flush an unsellable product and the less time you spend with it, the lower your losses in dealing with it. There is no point in trying to compete with instrument repair and calibration houses. Normally, the unit should be brought up to "clean used - appears fully functional - guaranteed to be serviceable" condition. Warranty repairs or trying to meet original specs are another game entirely. One that takes all sorts of special gear, NIST traceability, factory authorization, and expertise. In exchange for lower prices, the buyer is expected to assume more risk. While it pays to keep an inventory of crucial items for some popular gear (such as common hardware and Tektronix or HP knobs), stashing tons and tons of random replacement parts makes no sense whatsoever. If you do not like the vibes at any time or point during refurb, flush or downgrade the project. Never sell anything you feel bad about in any manner. The final key test is "Would you be
proud to keep this as a personal tool or instrument?"
Some of the simplest tools will often end up the most useful. Hex Allen wrenches, Vise Grips, and live power field tracers for sure. Potent cleaners and goop removers. Fresh adhesives that include silicon rubber (use most), epoxy, and superglue. Sources of repair and replacement items include a hardware store or two, Small Parts, W.W.Grainger, and McMaster-Carr. Plus, of course, such electronic houses as Digi-Key, Mouser, or as last resorts, Allied or Newark. Do not attempt any repair or refurb without having the bare minimum test equipment needed to properly deal with it. A modern oscilloscope (or its pc equivalent) is essential for just about any technical work. Be sure to research item demand before you even think about beginning refurb. Useful tools include present and past eBay sales, Google, Thomas Register, the Wayback Machine, or sci.electronics.design and sci.electronics.repair newsgroups.

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It is often possible to take a dozen broken identical items and end up with ten good ones by mixing and matching parts. This often will end up your most economical refurb and upgrading route. It is infinitely better to compete three of four refurb items than to have dozens of them piling up unfinished. Do not start any new projects before you eliminate some of the older ones. Second tier brands are probably not worth pissing over. HP (Agilent) and Tektronix test items are a lot more sellable than everything else put together. But HP Oscilloscopes are totally worthless, their last useful one being the 130C.

Tektronix Copyrights

Tektronix has recently and formally released the copyrights on all of their more obsolete test equipment. And eBay suppliers of varying quality have been rushing to make Tek service docs available on CD. I was particularly impressed by the aa4df CD that has 38+ service manuals for nearly all of the Tek 500 Series plugins. Typically at a $20 or so price. The 500 series consisted of mainframe power supplies of one through six slots that held individual single, double, and (rarely) triple plugins such as function generators, oscilloscopes, power supplies, counters, amplifiers, etc. While now somewhat long in the tooth, these remain highly useful for student or home use. While there is a hard-to-find and pricey extender card available, it is simplest to remove the cover of a TM503 and place the plugin being serviced in the center slot. This gives somewhat better access (especially at the front) than by using the obvious TM501. One recent TM501 repair found a separately dealt with plugin problem with a "broken" power switch. This was traced to a tiny piece of brittle plastic on the power control rod which was easily replaced by a pair of ordinary nylon cable ties.
Glass Beads and Shot Blasting
Ive always wanted a shot blast cabinet, because these are absolutely superb for refurbing water meters or finishing small metal parts or stripping paint or for removing rust or whatever. But these are huge and dirty and require access to a big time air compressor. One newer alternative is to add a shot blaster attachment to a pressure washer.

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Northern Tool has some nice ones for as little as $25. Getting the media can be a real hassle over shipping costs. Checker Auto specifically excludes this item from their "free shipping to your nearest store" policy. I found McMaster Carr to have the best mix of shpping and product costs. Search under "blast media".
Tek 465 Vertical Attenuators
The finest "aerospace era" oscilloscope of all time has to be the Tektronix 465. These remain an excellent choice in a high performance but somewat dated solid state 100 Megahertz oscilloscope. And units needing some repair or refurb can now be found at bargain prices. One 465 I was working on seemed to have extremely erratic attenuators. Normally the double gold cam driven contacts do not even need cleaning, let alone any service. But between the contacts was a pair of 10X and 100X plug in compensators. Reseating their pins a time or two cleaned up most of the problems in a big hurry. These are under the shields that say "Caution -- Delicate Materials".

Look for the Obvious

Sometimes the simplest and most mundane problems can produce the most outrageous symptoms. Ferinstance, back in the days of 4000 series CMOS, if you forgot to connect the power supply, chances are that the circuit would more or less work, but with rotten risetimes and frequency response. What happened was that any logic inputs that happened to be high routed enough supply power through the protection diodes to more or less make stuff sort of happen! On an oscilloscope of "second tier" quality, the symptom was a ridiculous overshoot on cal waveforms, combined with way too little amplitude. This was a plain old broken wire on the input BNC connector! The picofarad or two betwen the wire and where it was supposed to be soldered to was enough to couple the highest frequency waveform components. A touch of solder provided an instant cure.
Treat Antiques with Respect
Think twice and then some about refurbing really valuable antiques. Its super easy to do irrepairable damage and trivial to get in over your head. Ferinstance, plugging in an old tube radio to "see if it works" is guaranteed to cause smoke and fire because the electrolytic caps are near certain to be shorted. An associate asked me to rework a Weston panel meter that seemed to have a wide spread between "as is" and "museum quality restoration" pricing. Brasso and some Q-tips promptly revealed the totally unlegible nameplates were in fact near mint. A careful check with a current limited 9 volt battery showed me a perfect

34. 11

pointer and accurate operation. The unit seemed to be a low serial but clearly later variation on a Westons Model 1 with an 1880s patent date. The lack of a model number was very encouraging. Later eBay feedback determined a 1910 era date. Heres what the partially refurbed item looks like
The pumice or whatever in Brasso seemed to be about the right coarseness of abrasive, so I mixed it with orange super cleaner and again used Q-tips to scour the awful grime off the lacquered copper case. There was a finish break or two, but the improvement was otherwise spectacular. Repainting would obviously be a no-no because of the unique original red lacquered finish. The wooden bases cleaned up beautifully by cleaning, sanding, and oiling. Separating them was not advisable becuase of the complex wiring to the antique series resistor in the lower base. The item is now up on eBay.

Medical Gear and the FDA

Some medical gear can resell for outrageously high prices. Others are totally worthless, or may need one unobtainable part for refurb. Much of it may require a FDA Certificate or involve strict eBay Restrictions for resale. In general, med equipment is a lot simpler than it may first appear. But may do strange things in funny or dangerous ways. Thus, it is super important that you understand exactly what the instrument is intended for and all ofthe safety considerations involved in its use. In particular
Any items specifically involved in any way with life safety are best avoided entirely!

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I just picked up an autoclave sterilizer at an auction. Autoclaves are basically a pressure cooker that often runs at 121 degrees Centigrade and 15 PSI. These values are high enough to destroy all known organisms for medical sterilization or to provide curing for industrial adhesives, plastics, and related processes. It seems the "tatoo parlor" market is driving eBay prices for autoclaves quite high. This particular unit looked like all it needed was a "Sherwin Williams Overhaul". After a thorough cleaning I replaced the line cord and a broken fuseholder and a broken drain line and reglued and tightened or lubricated a few other items. The knobs and feet were replaced as they were mangy from outside storage. And the case was repainted. The seal looks just barely ok. After few more minor details, it promptly sold on eBay at a premium BIN price.

Playing the Slots

I was rudely surprised when the big pallet full of sealed slot machine display boxes had mostly upgrade pulls in it. At any rate, these rebuild fairly well with some effort, and we now have the really great results up on eBay. These are absolutely superb as a first student microcontroller or Basic Stamp project. These also are legal to own anywhere so long as the displays have no provision or mechanism for coins or tokens of any kind. But actual use of your final total design should obey any and all of your local or state regs. Heres what these dudes look like

Besides cleaning and an occasional broken pilot light assembly, the big usual problem was burned out bulbs. These turned out to be a standard long life incandescent bulb called a 657 that Jameco Electronics has for 15 cents each. Two reassembly tips following a total teardown: The cable retaining clip is best put in by loosely setting the wheel sideways on the frame up out of the road.

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The clip then snaps right in but otherwise would be a real bear. There is also a loose "U" bracket between the stepper and the frame. To avoid trying to hold too many things at once, use a pair of long nose vise grip pliers to clamp the bracket in place. This ridiculously simplifies reassembly. The 28 volt bulbs can be tested by dimly lighting them with any old 12 or 15 volt supply. The lower left socket pin is common, with the three horizontal pins on the same level being the low, medium, and high bulbs. The rest of the pinouts appear on our eBay Store. Because of the time and extra bulb costs, it doesnt pay to get too much ahead of actual sales. Keeping two units on deck ready to go and four diagnosed for repair seems to be about the right mix of risk and reward.
Avoid "TV Repair" Shop Items
I was suprised how much the value of tv repair shop items has recently dropped. Photofacts sell only marginally on eBay at four cents each, and full tube caddies seem to be not doing very well at $30 or less. The fact that old tvs even needed repair was telling. As was their lack of cable and video inputs, their huge size and weight, the hot chassis safety issues, their pitiful pre-comb color separation, their lack of regulation that left you with a tiny midscreen image and everything else wrapped around, and a need to reconverge your color alignment in a very painful process if you so much as moved the tv a few feet. Plus sound best described as mesmerizingly awful. All of which can get ugly when the old shop items get outrageously overvalued by whoever is trying to sell them. Especially if utterly obsolete stock is combined with Eico or Dumont or trade school kits or similar worthless marginalia. More on my earlier tv repair experiences in WAYWERE.PDF.

For More Help

See REFURB.PDF for an earlier tutorial on equipment reconditioning. Plus our DEGUB.PDF for additional debugging secrets. Extensive tutorials on auction buying and eBay selling appear in our Auction Help library. Our current offerings can be found on our Bargain Pages and by way of our eBay Auctions and eBay Store links. As usual, custom assistance is available per our InfoPack services. Further GuruGrams columns await your ongoing support as a Synergetics Partner.

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