Tools for PDP-8 repair

There seems to be some kind of persistent internet "meme" that you should use old test equipment to fix old computers (or radios).  Bullshit.

So this is a list of tools that either (a) you didn't know you needed or (b) you knew you needed but you either have or would buy the wrong one.  It doesn't include things like screwdrivers because (a) you already knew you needed them and (b) there are few bad screwdrivers.  So substitute at your own risk.  As an example, when I suggest that you need Polyphenol Ether contact lubricant, I don't mean that you should go to Fry's and buy contact lubricant because the generic idea of "contact lubricant" is good, I mean exactly Polyphenol Ether contact lubricant is good.

This page is all about doing things correctly with the right tools so they will last.  If you are the sort of person who uses car motor oil to lube your teletype because it's "good enough" this is the wrong page for you.

Am I missing something?  Write me, nabil AT

Teletype Toolsbender

I have a large collection (200+ items) of small teletype hand tools (including many for 5-level machines), so if you are local and need something special feel free to contact me for a loan. There must be lots of things to bend in a teletype because a 1/3 of them are various kinds of benders.

Crochet Hooks

These were sold by Teletype as "spring pullers" and a very handy for hooking and unhooking the small springs.

Needle Oiler and 3-IN-ONE Motor Oil

3-in-ONE oil

Needle Oiler

You should really use a pin-point or needle oiler, you want to minimize the excess oil drippings which will attract dirt.  Cheap needle oiler bottles are commonly available from firearm tool dealers (get one with a very long, very thin needle).  For the general use KS7470 oil 3-IN-ONE Motor Oil (blue bottle) is a reasonable commonly-available turbine oil and certainly safer that any of the other crap people suggest like car motor oil or WD-40.  The 3-IN-ONE motor oil is a hydrocracked paraffenic base with corrosion inhibitors which seems to be close to the military substitute (a paraffenic turbine oil) of the original KS7470.  I own 4 pints of original KS7470 teletype oil but usually just use the 3-in-one oil instead.  It smells different than the teletype oil but it's not unpleasant.  If you are have the time to do the research a pure synthetic oil could probably be found with better properties, for example the Nye Synthetic Oils, but many of these synthetics can attack the plastics in a teletype.  I occasionally use a synthetic spindle oil w/PTFE on a part of the keyboard because of the low return force involved. 

For the KS7471 grease I and many other people use Lucas Red 'N' Tacky #2 but without much analytic justification other than experience.  Note that some of the teletype lube instructions require mixing the oil and grease 50/50 so you'll want to test the pair for compatibility.

Atlantic Research Corporation DTS-1/Data Tek 9600

These are serial terminal test sets geared towards teletypes.  The most used bit is the pattern generator (several test messages and a programmable 4 character custom sequence for test loops) with selectable code level/bits (ascii/ebcdic/baudot) and distortion.  On the receive side there there is also a one-character receiver (on LEDs) and several extremely useful things for teletypes like a loop current meter and distortion analyzer.  They'll do 20ma/60ma/polar current loop & RS-232 (which has a nice little patch and switch section). There are a couple versions, one with an EEPROM on the front for custom test message and one without (there is no advantage to the EEPROM version). They are the first tool I go looking for to work on my teletypes.

At one time I bought one that had some kind of factory modification done to it, it was the highest quality work and involved adding another circuit board (3 transistors, a hex inverter and an optoisolator), the front panel had the topmost loop output plug replaced with a BNC connector and 3 binding posts installed above the RS-232 connector.  I'd avoid buying one with these modifications.

I have several of these, contact me if you are local and need to borrow one.

Tygon/Plastic/Rubber tubing for replacing model 33 hammers

Every 33 hammer I've seen is gooey and must be replaced.  Even the box of factory new hammers I have hammers is gooey!  These will deform rapidly causing the metal striker to hit the type wheel, quickly destroying it.  The best solution is to remove all the hammer residue and get some rubber or plastic (I use a soft plastic) tubing the fits snugly over the metal striker.  You are trying to match the original (quite thin) dimensions, so don't get something so stiff and tight that it bows up, get something reasonably soft and conformal.  Cut it quite short (1 cm) to minimize the mass. People will suggest all kinds of other things like rubber bumpers, but when it falls off because the adhesive fails and the striker hits the typewheel you are instantly and irrevocably screwed. 

General Tools

A modern soldering iron

Weller 921ZXIf you are like me, you have a Weller WTC-series soldering iron somewhere on your workbench. These were the mainstay of the industry, and used a curie-effect temperature regulation system (each tip programmed the iron for a different temperature). They were low-voltage, grounded-tip, and reasonably safe (for a sub-$200 iron).

Times have changed, it's time to get a new iron. Although the newer generation of the WTC series started incorporating better ESD protection, they couldn't eliminate a fatal design flaw, and that was the arbitrary times when the heater kicked in and out, creating a EMF spike which can be coupled into your workpiece.

Weller makes several new irons that use zero-crossing (electronic) control along with much better ESD control and protection again stray currents and fields. The EC series is nice, and ranges from $200 to $400. The Weller 921ZX1 is an inexpensive alternative (I picked mine up at Fry's for under $80). It has a slide control for setting the temperature (in degrees, not "watts", which is useless like the cheap ones), and reasonable selection of tips from the beefy to SMD. A nice feature is a bi-color LED which monitors the heating circuit's power output ratio. The picture to the right is the 921ZX.

If your soldering iron isn't temperature regulated it's useless for computer work.

If you can find a used one Metcal irons are very nice.

Avoid:  Cheap unregulated temperature irons, non-ESD irons, arbitrary thermostat irons.  The 921ZX is good and inexpensive.



Edsyn SoldaPullt

Solder braid is handy, but these are simply the most useful piece of desoldering equipment.  The full-size ones are the best, get one of the ESD safe versions, not the blue one.  Indispensable.

Squeeze-type IC Lead Straightener IC Lead Straightener

Most straighteners are from bad to useless, this one is by far the best of the ones I've used.  Radio Shack used to sell them,  Jameco has them now.  The other side is for 16 pin DIPs.  It's conductive plastic, you just drop the chip in and squeeze.


Service Chemicals

DeoxIT (the red ones)DeoxIT

DeoxIT is a group of service chemicals for restoring electrical contacts & plated connections. It is reactive, and actively removes corrosion and oxidation. It is also somewhat persistent, and will remain on connectors that are mated and unmated, moving wipers, etc. DeoxIT is well known, recommended by several OEMs, and generally compatible with most materials. Personally I only use it when I'm dealing explicitly with corrosion, oxidation or on high-current applications (like power supply connectors).  Deoxit is especially vital on high-current mated molex power connectors where an I^R/mechanical thermal runaway effect routinely destroys them, for example the J4/J5 power connectors and fuse holders in an 8E, but you need to do it before the damage starts!  There are several concentrations from 5 to 100% for various applications, I'd stick with the low concentrations (the base product is an oleic acid derivative) for splashing around.  Spraying a bunch on a clean rag and then using that to clean off dull-looking card edges seems particularly effective and leaves some behind to clean the mated connector.

Avoid:  WD-40.  Any other contact restorer. Using too much, using on uncleaned contacts, using on things that are exposed and can attract dirt.

Polyphenyl Ether contact lubricant

I use this to make card insertion easier but these can also reduce contact resistance (a lot!).  If the product is pure PPE & carrier there is really no downside to using these on any high-insertion force connector, they can only help.  Very handy for OMNIBUS cards (spray on the card, not the backplane).  PPE is a very light lubricant, non-reactive, non-conductive and typically with few compatibility or contamination problems. It must be replenished if you do frequent insertion/removal cycles. The 6-ring version is a little more viscous and a little longer life. Specifically avoid the "wipes" products, they leave little strands of the pad stuck to the sharp bits of a card edge which are a real hassle to remove. Just get the aerosol spray or liquid (not pure, 2%). Use is simple, clean the contacts first if they are dirty,  spray the PE on, let it dry. For those of us with the occasional brush with modern computers it's also what I use on big pin count packages like Intel 486's when the need to go into a normal (i.e., not ZIF) socket.  MG Super Contact Cleaner and Techspray Rid-Ox are two industrial grade products you could try, but there are also "purer" aerospace/aviation grades.  You want one that evaporates completely without any extra oils or junk, I liked the Chemtronics Gold Guard as it only had alchohol and PPE in it, but I'm not sure if it's made anymore.

Avoid:  Anything except Polyphenyl Ether contact lubricant.  Any of the 'wipes' products.

Heptane label removers: Original Un-Du and BestineUn Du

They are 100% Heptane which is absolutely the best label remover.  It has relatively low toxicity (nor has it been identified as a carcinogen) and is compatible with most surfaces and materials, including plastics.  Un-Du has a very nice scraper, so if you can find an original bottle, get one.  Bestine is much cheaper, from 1/2 to a 1/4 the price, but it doesn't come in the little dropper bottle or scraper.  Until you have tried Heptane as a label remover you can't even begin to appreciate it, there is no comparison, it's not "a little better" or "20% better", it is 1000% better.  The downside is it's almost instantaneous evaporation that can make it difficult to to use.

Avoid: Reformulated (California, VOC safe) Un-du.  Anything with xylene, toluene, benzene, acetone or methylene chloride in it.  I like to avoid methanol (methyl alcohol) as much as possible.  Goo Gone Xtreme Remover (toluene, acetone & methanol) would be top on my 'avoid' list, but it probably works great.

HP Logic Dart

Logic Tools

HP E2310A LogicDart

It’s a small, hand-held 3-channel logic analyzer (or small digital scope) with an LCD display, the nice thing about it is that you can program the logic threshold, so it can be used on things like ECL and negative transistor logic computers.   Very light, it's reasonable to use as a logic probe (nice lights and beeper), I particularly like the needle-sharp probes. Discontinued, but HP still has this data sheet online.

Avoid: Buying these without the special probes, they are useless without them.

Tektronix P6401 Logic Probe


Mostly I use my LogicDart, but a stand alone logic probe is very handy, especially one that is easy to read like the Tek with it's bright, omnidirectional red and green lamps right at the tip.  The "memory" is easy to use and inuitive, it allows you to catch a transition without watching the probe.  The Tek uses incandescent lamps, only TTL/DTL and not very electrically rugged but I have yet to find any other that is the perfect combination of functionality, size and ease-of-use.  If you are searching for one on ebay, don't accidentally get the version with the BNC on the end, the one you want has a red and black power clip.

The HP 545A would be my second choice (has a long sharp tip & CMOS mode) but the indicator uses OFF/DIM/BRIGHT instead of Tek's RED/GREEN. It's long, thin body can be an advantage over the Tek's short stubby one but I still prefer the Tek, the performance and human interface is just perfect. If you are using a logic probe you don't want to be thinking about it how to read it, you just want it to be a transparent little visualization of the circuit node.  That's what the Tek is.

Avoid:  Probes where the indicator is on one side or can't tell the difference between "not hooked up" and "low". Logic probes with LEDs on the top of a flat box are just silly.

HP 548A Logic ClipHP 548A Logic Clip

"The Logic Clip is an extremely handy service and design tool which clips onto dual-in-line package (DIP) ICs, instantly displaying the states of up to 16 pins. Each of the clip's 16 LEDs independently follow level changes at its associated pin. Lit diodes are logic High, extinguished diodes are Low."

The HP catalog says it best, "extremely handy".  A few other companies made these but they are 2-3x the size and clumsy.

I have several of these, contact me if you are local and need to borrow one.

HP 10529A Logic Comparator

"The HP 10529A Logic Comparator clips onto powered TTL or DTL ICs and detects functional failures by comparing the in-circuit test IC with a known good reference IC inserted into the Comparator. ... Any logic state difference between the test IC and reference IC is identified to the specific pin(s) on 14 or 16-pin dual in-line packages on the Comparator's display. A lighted LED corresponds to a logic difference. Intermittent errors as short as 300 nanoseconds (using the socket board) are detected, and the error indication on the Comparator's display is stretched for a visual indication. ..."HP 10529A Logic Comparator

If that isn't clear enough, you clip onto a chip, the inputs go to the inputs of your known good reference IC, the outputs are XOR'd with the outputs from the circuit and displayed on a display. If you see a light, that node in the circuit isn't following your reference chip. Reference chips are on little carriers you program (by drilling!), you can build up a library of common devices for your system(s) of interest. There is also a generic card which can be programmed by dip switches for one-off tests.  These often came in kits like the 5011T with logic clips and probes.

I'm building up a library of pre-programmed cards for common PDP-8 TTL chips.

Blank reference cards are HP part #10529-20005, a package of 20 was available as model #10541A.

I have several of these, contact me if you are local and need to borrow one.

Avoid:  Paying too much.  Just be patient, you can probably get one for $30 or less.

HP 546A Logic Pulser

Pulls a logic node to a different state.  The trick that make a pulser possible is that it uses a very short pulse (500ns), hopefully not enough to blow up the output gate of whatever it's fighting against.  Without a pulser you are stuck with the natural state/signals in the device, a pulser allows you to inject your own, and are commonly used with a current tracer or logic clip/probe (they have built-in pulse stretchers to make the short pulses visible). The 546A is nice because it can inject a fixed number of pulses or a pulse train, is TTL/CMOS selectable, and is also auto-polarity (it'll pulse the line the "other" way). 

General Circuit Testing

HP 547A Current Tracer

“The HP 547A Current Tracer is a hand-held probe which enables the precise localization of low-impedance faults in electrical systems. The probe senses the magnetic field generated by a pulsing current internal to the circuit or by current pulses supplied by an external stimulus such as the HP 546A logic pulsers. Indication of the presence of current pulses is provided by lighting the indicator lamp near the current tracer tip. Adjustment of probe sensitivity over the 1 mA to 1A range is provided by the sensitivity control near the indicator. The probe is self-contained and requires <75 mA at 4.5V to 18V, from any convenient source.”

I don’t use this very often, but when I need it, I really need it. It’s used for finding things like shorted input gates, stuck tri-state buses and broken/shorted traces.

I have several of these, contact me if you are local and need to borrow one.

General Radio (GenRad) 2220 Bug Hound

Genrad 2200

This is similar to the HP 547A current tracer except that it contains it's own current source and the probe has directional indicators that let you know which side of the probe the wire is on. This is very handy for tracing wire-wrap connections.  It also has some other milliohm continuity/tracing functions.

I have several of these, contact me if you are local and need to borrow one.

Zero Beeper

This is a continuity tester that uses an extremely low voltage (say, 100mV) so that it won't turn on any of the semiconductor junctions in a circuit. I haven't seen many around recently, but Contact East (a good source for almost every tool on this page) private labels one, the Zero-Current Audible Continuity Tester. It is a must have tool when you are trying to trace out continuity on a circuit board.

Avoid:  Any other kind of continuity tester for PCB work.  Never use the Ohms, Diode or Beeper function on your DMM to measure continuity on a circuit board!

Huntron Tracker 2000 (or similar)Huntron 2000

This is sort of an in-circuit curve tracer who's use is more "art" than "science".  Mostly for power supply repair, especially switchers.  It displays a current vs voltage plot and with a little practice it's easy to recognize the patterns of good components and common failures. Has some applicability for testing passives and small junction devices, I wouldn't recommend using it on ICs even though many people do.  They can be expensive, used ones easily fetching over $500.  There are trackers other than the 2000, but it's the one most commonly available.  The 2000's "low" range is a bit overpowered, the newer models have more usable low ranges.  There are a few "huntron like" devices, Vu-data and Tenma make one, and I've seen an inexpensive ($200) LCD model on Ebay.  There are also standalone boxes that turn an XY scope into a Huntron-like tester.  If you are doing lots of switch-mode power supply repair you might also consider getting a ringer like the ones built into the Sencore Z-meters or the Blue Ring Tester.

IC Test Clips3M Chip Clip

If you are trying to diagnose a logic problem you'll often be struggling trying to keep 20 grabber leads in a rigid precise arrangement so the hooks don't pop off and/or short out adjacent pins. What you need are a Chip Clips.  This is something that looks like a large clothespin that you clamp around the chip, with it you can access each signal via is a pin that is routed to the top of the clip without any danger of shorting.  3M, AP and Pomona all made Chip Clips (or "IC TEST CLIPS"), I like the 3M gold plated ones.  They are commonly available in the $5 to $15 range.  Ones with pin numbers are nice.  There is a trick, you cut the little plastic plates used for wirewrapping that have pin numbers on them in half and put a half on each side, then you have pin numbers.  Note there are two styles of top pins, one with what look like nail heads (best for manual grabbers/scope probes) and ones that are straight.  The straight ones are handy for use with logic analyzers as you can slide a standard connector right onto them.

Tek Scope Current Probe (for core memory repair)tek p6022

Only absolutely required if you are fixing core memory, but they can be useful just to tune it. You want the tiny, tiny little sensitive ones.  There are a couple versions, AC only and AC/DC, I think you only need the AC which are much cheaper (mine are AC/DC and require an external TM500 amplifier).  I'm sorry I'm not recommending a specific model, check the docs of what you are working on for the bandwidth and sensitivity requirements.  P6022 shown, check out the P6021 also.  About $200 on ebay.  For the straight-8 there is a rather rare single-height extender card with individual current loop wires.  On the older OMNIBUS core there is a little wire loop (which was removed in the last revision).

Transistor testing

The one built into your DMM is crap.  Forget about using curve tracers as transistor testers, it's not practical.  The cheap little LCD parametric (DY294) testers are equally useless as in-circuit testers, and in circuit is a must. (For out-of-circuit testing and identifying is the Peak Electronics DCA55 is good.)  Avoid the 1950/60 vintage testers, things built into tube testers or more simply avoid everything that isn't on this list,   Note that in-circuit testers are better at some failure modes than others, parametric shifts (like excess leakage, which often gets worse) might still test good in-circuit.  Fortunatly transistors usually just fail "busted" and a simple in-circuit test is all you need.

NB: I removed the Sencore TF46 since people are using this guide to select which piece of test equipment they are buying for a particular task  The TF46, although good, was inferior to B&K and no comparison against the Vu-Data & Leader.  The Seccore switches are just too flaky, the 520B seems to be able to do in-circuit better and the TF46 uses really crappy, thin wired-in leads (which are always breaking at the ends) instead of banana jacks.  I'm sure some people prefer the TF46 over the B&K.

B&K 520B
    (common)B&K 520B

Lead permuting is a 6-step rotor, PNP/NPN identification is automatic.  These seem to be able to do a better job on in-circuit devices shunted with low impedances than the Sencores because of their test method and their high drive range is quite high (250ma, 4% duty cycle). I like and use my Vu-Data and Leader much more than the B&K, but it's solid, commonly available and works well.  Note the parametric test is leakage & Si/Ge, not gain, this is fine for computer work.

Vu-Data 5110
    (hard to find)

Vu-Data 5110

This is an older (circa 1990) tester from the Navy.  Typically they'd come in a padded bag and would often include probe sets (bed of nails and clips), fuses, spare sockets and a manual.  Although complex, they are rugged electrically and easy to repair using only standard parts. AC powered only.  In addition to the in-circuit tests they have an almost entirely independent, parallel parametric section (including Si/Ge identification).  These have several features I like: a continuously variable drive for in-circuit tests, a display for the permuter (there is a digital display that shows E B or C above each lead as you rotate the switch) and of course a beeper.  An unusual function is the ability to detect several shorted/open-device failure modes in-circuit and identify them.  Each lead of the in-circuit tester side is individually fused and it claims to be able to withstand up to 600v of accidentally applied voltage.  Here's a local copy of the manual.

I have a couple of these, contact me if you are local and need to borrow one.

Leader LTC-906 and LTC-906A
    (very hard to find)

This was the first transistor tester I used as a teenager in a professional repair capacity. I didn't think much about it at the time, it was just the one on the bench.  In the dusty eBay LTC-906 I have the date codes are 1977 which means they predate even my early experience with them by yet another 10 years.  They are surprisingly complex for the size (and age) with about 20 ICs and are very well put together. Comparing one of these to a Sencore Cricket would be like comparing a 707 to a Cessna.  Does both in-circuit go/no-go and out-of-circuit parametric (and Si/Ge).  What's so great about them?  They self-permute their lead arrangement (and the PNP/NPN selection).  No switches to turn or buttons to push.  So you just poke at the transistor and if it beeps it's good (it identifies the pinning and type on LEDs).  The is an important feature when your computer has several thousand transistors.  Downsides, well, these are very old.  They don't contain anything unusual, the schematic is available, but they are OLD.  Also the test leads are unusual in that they aren't banana ended, they have a 3-pin comb you stick into the transistor socket.  So if you get a used one check that it comes with leads or you'll need to make a set.  The Leader transistor test clips (the banana jack versions) and probe became an almost industry standard and are what come with the Vu-Data above (and are probably the right ones for the B&K).  The 906A is a horizontal layout of the 906 with the same functionality but newer. They removed the E&C indicating LEDs (superfluous, they are just the inverse of the B LED) and it has easier access to the battery.

Capacitor testing

Used mostly to look for bad electrolytics. Since 98% is checking in-circuit capacitors for ESR a standalone ESR meter is probably the most useful tool. For very large caps that you can disconnect and measure you are also interested in leakage. Capacitor values rarely change, a "capacitor meter" is useless as a test tool. 

Avoid: Capacitor meters, radio cap testers, Vintage Eico/Sprague/Paco/Heathkit testers, units with magic-eye or tuning-eye tubes, anything built into a DMM or LCR meters & bridges.

Sencore LC102

Sencore Z-meters

Any of the Sencore Z-meters such as the LC53, LC75, LC77, LC101, LC102 (pictured) or LC103 would all be good choices for large electrolytics that you can isolate, used LC53 & LC75's are routinely on Ebay for under $200.   The lower end are out-of-circuit only.  As you progress in price some have the ability to measure ESR, some ESR in-circuit and then in-circuit capacitance as well as ESR.  I'd say you'd virtually never need a tester like this for digital board repair, only analog, power supplies & motor run caps.  Some of these have ringers which are good for SMPS and monitor repair.

Almost any Standalone ESR meter

Measures the most common failure mode of capacitors. Hands-free and a beeper are nice features to have.  In-circuit is a requirement, you want one with a very low p-p output voltage (<20mV) and you'd like something at least a little electrically rugged (or repairable) so it doesn't blow up when you accidentally hook it up to a charged cap.  I use a CapAnalyzer 88A most of the time (on modern stuff),  it also does a DCR (short) test, but the probes are really designed for small chip caps.   My next purchase is going to be a Capacitor Wizard with the protection kit. Along with the more convenient leads, these are 5mv, high-accuracy (log analog meter) 100khz testers and they have a beeper which is handy.  You can use some ESR meters as a sort of continuity/leakeeker-like device for finding shorts.  Also see Anatek's Comparison of ESR Meters.

Tenma ESR meterTenma ESR meter

Another of my favorites is the Tenma ESR meter (discontinued, but routinely on ebay for about $50) low accuracy & only 50KHz but almost indestructible, in fact some people use it on live circuits, great for the big filter caps that I'd be afraid of subjecting the 88A's auto-discharge to.  People seem to unfairly rag on this tester, but it's the one I grab first for poking at unknown electrolytics in power supplies.  There is a failure mode you should be aware of, it you are going to be dropping it or slamming it around the DC blocking capacitor on the input is so big and heavy that it can break the solder lands it's attached to.  It's easy to insert a big glob of hot glue under it to prevent this. I'd suggest replacing the supplied test leads immediately with some nice (non-plated) ones.  A drop of DeOxit in the banana jacks wouldn't hurt either.  From looking at the circuit I'd say the Tenma is a cheap clone of the original Creative Electronics ESR meter (which was a well-regarded tester).

Wire Wrapping


Manual wrap/unwrap tools

Electric wrapping tools

Standard Pneumatic is what you are looking for, but I have used the Gardner Denver with good results. 

Avoid: Hobby brands or battery powered units.

Cut, Strip & Wrap (CSW) bits

CSW is the light sabre of wire wrapping.  You stick the wire in, put it over the terminal and zing it strips the insulation off, wraps the connection and cuts the wire.  The bits and sleeves are individually serialized, precision matched and calibrated for exactly one wire gauge and insulation.  When using CSW bits you tether your gun so it cannot hit the floor (not kidding).  Bits & sleeves can cost $300 for the pair.  You do not lend out CSW bits to even your oldest and most trusted friends.  CSW wrapping is very dependent on the wire insulation, you typically pick a special tefzel type, not just generic wire wrap wire.  Home ]