Tools for old computers
Substitute at your own risk.
A modern soldering iron
![[Weller 921ZX]](images/921zx.gif)
If you are like me, you have a Weller
WTC-series soldering iron 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.
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. I don't do much soldering anymore, spending $400 on an iron would have priced each connection in the several dollar range. 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 really 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 at all, it's useless (for computer work).
If you can find a used one, Metcal irons are very nice.
A scope
There was some recent discussion in
alt.sys.pdp8 recently about scopes. Someone advanced the idea that
old scopes were preferred for fixing old computers, a theory that
I and several other people violently disagreed with. You need a
modern, reliable scope, not one that sometimes has flaky
triggering, gain mismatches between channels and a drifting time
base (or one that is going to develop these problems!). I’d
suggest an analog scope unless you are very familiar with the
limitations of equivalent-time sampling or can afford one of the
very newest color Tektronix “digital phosphor” scopes
that have fast real-time sampling. Just about any ‘90s
vintage 100mhz scope is probably fine, although most experienced
people would select Tek scopes as the best. In particular,
look for a Tek 2236, 224{5,6,7}, 2445, 2465 or 2467. The
Tek 2467B is simply the best analog scope you can own, bar none.
A Zero Beeper
This is a continuity tester that uses an extremely low voltage (say, .1 V) 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 TesterIt is a must have tool when you are trying to trace out which pin of a connector goes to which IC on a circuit board.
Ideal 61-038 STAT GARD
This is one of those three neon light outlet testers, and will
indicate all combinations of open and transposed
hot/neutral/ground leads. In addition it has a plug for a
(supplied) long coily lead that you attach to your wrist strap.
DeoxIT
DeoxIT is a group of service chemicals for
restoring electrical contacts, plated connections, pots, etc. It
is reactive, and actively removes corrosion and oxidation.
It is also 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 or oxidation. For general use on gold-plated
connectors to reduce insertion force, I'd recommend using a
polyphenyl ether based product instead.
Polyphenyl Ether contact spray
I use this to make card insertion easier. It's a very light lubricant, non-reactive, and typically with few compatibility or contamination problems. It must be replenished if you do insertion/removal cycles. 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. Use is simple, clean the contacts first if they are dirty (with something like "blue shower"), let them dry, spray the PE spray on, let it dry again, and insert. 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. I don't know the part number, but TechSpray make some, but the one I most often find available is Gold Guard from Chemtronics.
Cleaner/Degreaser
The best are (were) the CFC based ones like the original Blue Shower. If you see any of this (or it's kin) as old stock someplace, certainly buy it (or let me know where it is). Be very, very leery of any CFC-free replacement cleaners, these often contain both highly reactive and toxic components. Look at the ingredient list carefully of anything you are buying, a general rule would be the fewer ingredients the better, preferable just one (or one and a propellant). Note that methyl (unlike ethyl) alcohol is bad for you, and methylene chloride is really bad for you. There are often other bad nasties hidden under unfamiliar or uncommon names in what seems to be a deliberate attempt to keep people from knowing how dangerous the product is. Certainly try to get the MSDS for anything you buy. Anyway, what I use as a non-CFC cleaner is pure HFE-7100 (as found in Tech Spray's HFE Cleaner/Degreaser 1685), it has acceptable cleaning, wetting and solvent properties as well as an excellent safety profile. Unfortunately it is also very expensive, perhaps $20 for a can. Another good alterative is pure HCFC225 Asahi (like Tech Spray's Asahiklin AK225), which has a low Ozone Depleting Potential and should be around for a few more years. Buy it while you can.
HP 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".
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. ..."
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.
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.
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 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.
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.
Fluke 9010A Micro-System Troubleshooter
Microprocessor era, but still old. Very popular (too popular, they keep driving up the ebay prices) with the video game collector crowd. The 9010A is a small keyboard controller that connects to a pod, the pod has a plug which is plugged into the CPU socket of the target system. The magic is the 9010A now totally controls the target system, and can read and write the address space of the CPU, exercise I/O, everything. Cool features like a "learn" mode which sweeps the address space and identifies RAM, ROM and I/O, bunches of tests for detecting stuck address/data lines, etc.
There is a logic probe that was available for it, but they are hard to come by. It was mostly used for pre-written testing "scripts" and signature analysis. Pods that I have seen are 6502, 6800, 8080, 8085, 8086, Z80, 9900 and 68000. There are probably 8048, 80186, 80188, 80286, 6809 and 1802 pods also.
There is a model 9100, uses the same pods, but is much more powerful and can drive 32 bits pods like the 80386 and 68020. Unfortunately the software is node-locked, if it doesn't come with the disks it's almost useless.
A transistor tester
Small-signal is easy, power is harder. Auto-lead
identification and in-circuit are very handy. A Sencore TF-46 would be a good
choice for small signal testing. They are now only available used, but if
you can find a working one the Vu Data 5110 is a good almost "lab"
grade testers with Beta tests at different currents, Si/Ge identification, wide
leakage ranges, etc. Although it's missing Ft tests, this shouldn't be an
issue in computer work. The Vu Data has digital meters and an unusual
split-tester design where one half of the tester is for parametric tests out of
circuit and the other is for in-circuit. Each half has separate inputs and
device jacks.
A capacitor tester
Used mostly to look for bad electrolytics. The important
features are the ability to test for leakage and ESR, capacitor value rarely
changes. Any of the Sencore
Z-meters (such as the LC55, LC75, LC101, LC102 (pictured) or LC103) would all be good choices, however there
are many inexpensive units available as well. Almost any tester
will test for value and leakage, but ESR is the key feature you
are looking for. Another good investment
(if you can't afford the Sencore LC103) would be a standalone in-circuit ESR meter,
which are available in the $50 to $150 range. You really need in-circuit
ESR for things like switching powers supplies.
I'll mention the ZM-3A here, it's a military capacitor tester often seen at swap-meets. Once you have seen one, you can spot them a mile away, they have a distinctive red/green paint job. Although tube-based, they are exceptionally rugged (and heavy, 50lbs!), accurate, and doing almost everything. They also measure "power factor", which is related to ESR. If you see one for $50 or less, get it.
An ESR meter
Measures the most common failure mode of capacitors. In-circuit is a requirement for any stand-alone unit. I use a Cap Analyzer 88A most of the time, since it also does a DCR (short) test. Another favorite is the Tenma ESR meter, poor accuracy but indestructible, in fact you can use it on live circuits! Good for the big filter caps (the 88A has a somewhat inconvenient probe for large caps) that I'd be afraid of subjecting the 88A's auto-discharge to. Many people like the "Dick Smith" ESR meter than is available as a kit.
Genrad 2220 Bug Hound
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.
AN/USM-118 / Hickok 1234 "cardmatic" tube tester
I did say "old" computers, didn't I? Although this wouldn't be the greatest tube tester for golden-eared toob audio applications, it's the cat's meow for testing bunches of tubes quickly in your ENIAC. It has tests specifically designed for tubes used in computer applications. Tube setup is done with pre-programmed cards that set all of the characteristics. The only limiting factor in how quickly you can test is how long it takes for the filament to come up! It's a standard transconductance tester, and has the usual bells and whistles for shorts, gas, leakage, etc. There is a little trap door which conceals even more arcane test functions should you need them. A military version and a Bell telephone version also exist, the military being the mostly likely to be had on today's surplus market. Also see my USM-118 / Hickok 1234 web page for more information.
A 20K ohm/volt VOM
In addition to you DVM, you'll probably need
an old analog meter as well. Why? Cause in 1960 they didn't have
DVMs (they had VTVMs, but nobody carried one of those in their
toolkit) and most of the calibration/repair procedures you will
find are written with the VOM in mind. This time you have two
choices, both are excellent, and they are the Simpson 260 and the
Triplett 630. I like the Triplett a little more than the Simpson,
but keep in mind the Triplett uses a weird 30v battery and is 10k
ohm/volt on it's 250mv range. In either case, be sure to spend
the extra $ to get the version with overload protection.
Where to buy this stuff