Comark test gear - info sought

[Phil G4SPZ]

I have been given a couple of pieces of Comark test gear, and managed to restore them to working order. However I've been quite unable to find any user instructions, service information or circuit diagrams, other than brief references in Wireless World dating from 1968/9. The units are:

Comark Electronic Multimeter Type 1231 (1969)
Comark FET Tester Type 185 (1968)

The electronic multimeter works well on all but the DC voltage ranges, where it reads 4% low. The FET tester appears to work and gives meaningful readings when testing known good FETs, although I am guessing at the operating procedure as I have no user manual.

Other normally reliable sources have drawn a blank - can anyone help please?

Phil

[AlanBeckett]

Comark still exist and apparently now belong to Fluke. Their Website doesn't appear to have any Manuals, archived or current - very odd.
I'm assuming it's the same Company. Perhaps an email to them might find a friendly soul.

Alan

[Phil G4SPZ]

I've already done that, Alan, and I received a polite reply to the effect that "the company has been bought and sold a number of times since 1969, and no details of such old equipment exist"... the Comark brand name now appears to be confined to a range of temperature measurement instruments.

I often think it's a shame, though perfectly understandable, that many manufacturing companies attach so little importance to the products they made in the past.

[AlanBeckett]

Ah, so, I was hoping they might still have an Od Codger with a stash. Even Industrial Grade Gear seems to have joined the rest of the Market and after a few Years just gets abandoned.

Alan

[Mark Hennessy]

They're a new one on me, Phil...

My usual approach to this would be to reverse-engineer the schematics. Often easier said than done, but I quite enjoy it, and find it rewarding. If it's suitably obscure, I'll put the results on my website and/or the forums to preserve the information. Either way, once drawn up, the operation and calibration is normally easy enough to determine.

Good luck,

Mark

[Phil G4SPZ]

I agree, Mark, and that's what I'll probably have to do for the multimeter, although the FET tester is working OK - I am looking for the operating instructions for that. 

I've reverse-engineered a handful of odd things in the past, and at least gear of this era has discrete transistors in it, so I'm in with a fighting chance. Chips, though, usually make my blood run cold, although I have succeeded even with them - the internet is a fantastic resource for quickly looking up type numbers and pin-outs!

It just seems odd that Comark isn't 'preserved' at all on the 'net, unlike Advance, Marconi, Tektronics and the better-known test gear brands.

[Cleggy]

I've got two old but useful bits of Comark kit; a thermocouple thermometer and an insulation tester. I think I picked up both from rallies for next to nothing and both work, though the insulation tester went bad for a while and I had to trace out the circuit of that. The latter is very useful when testing old caps as it it will run up to 500V (working from 8 C-cells). Sorry, but have no info on your particular instruments.

C

[wme_bill]

I have a manual covering a variety of Comark 1600 series analogue thermometers.
They all use DC chopper amplifier, on board 1600/2, input to 30mV to output to 1V driving a 500ua meter, which is packed in together with various range and thermocouple stabilised power supplies depending upon the ranges required.
I wonder if that is also used in the multimeter, and would ber useful to you. It uses 9 BC183 transistors and 3 small diodes 1S920.
I also have the Insulation Tester 1905, (dated 1971) currently waiting for a roundtuit spare part. Range of test voltages, 25V to 1kV. Uses a transistor oscillator, driving voltage doubling/trebling rectifier. Measured with a 10ua meter. The manual also has a circuit for a later version (dated 1980) which uses a couple of Op.Amps and drives a 500ua meter. I got this from them in 1996, when they were at Welwyn Garden City since around 1991, having left the previous address at Littlehampton, Sussex around 1980. So perhaps you can work out who took bought and sold the business from these dates.
wme_bill

[Mark Hennessy]

Well, if anyone would know about Comark, it would be Bill

Welcome to the forum

Needless to say, feel free to post data here - the attachment allowances are pretty generous.

All the best,

Mark