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Not easy but will done.

Great Job.

That complex yet convenient (and idiot-protection?) line voltage switching system appears to be a potential source of a "single-point failure" which, if faulted, will destroy the rest of the unit. In a medical instrumentation and aerospace systems, unacceptable. Is this what happened here?

Really interesting repair video, Ian. Thank you! Finding calibration standards for these instruments is a challenge for hobbyists. I am currently repairing a Keithly 619A dual channel electrometer and Keithly provides a calibration procedure for the 20 nA range that uses a 1.9 volt source (PDVS2Mini - of course) and a 100 Mohm resistor to provide 19 nA. Perhaps you could use a similar method on the picoamp range of your 440. My biggest challenge has been coming up with a 19 Gohm shielded and guarded resistor to calibrate the 20 Gohm range. Regards, David

Love this acsent! Especialy cler pronounced "R". Good job too, very explanatory! Greetings from Bulgaria!

I have an old HP boat anchor picoammeter and the calibration procedure uses high value reference resistors and a basic power supply. Getting hold of some multi gigaohm 1% resistors might be another option for adjusting such equipment, without needing to push your 220 to its limits... or maybe try to find a Keithley 261, like I think Dave Jones has (lucky so and so).

Well done. I have one of those and a couple of fancier digital supplies, but the simplicity and quietness of that one means that I use it 95% of the time. Great little unit.

Awesome vid as usual. Thank you Ian.

after 50 years most things start bulging...

Great job as usual Ian. I love repairing electronics and keeping them out of landfill as well. At the moment I am working on a 55 inch LED TV that shuts down after 20 minutes. Has got me scratching my brain a bit, but I'm sure I'll get there in the end. I like your diagnostic techniques and analysis of schematics as well. Keep up the good work! 👍😊

my 88 year old mum who was watching over my shoulder asked what it did, I pointed out it was a current meter! her reply to that was can it measure sultanas. 🙂

The 225 has a "off" position for the fine tune, which should be used to set it when calibrating to ensure a consistent setting, turn it fully left and you will feel it click in.

1:00 Is that really 4 nixies? The board inside had just 3 nixies on it. Is the forth digit in front of the 3 nixies just a neon bulb that serves as a 1 indicator? Guess this can be refered to as a 1999 count meter 🙂 Nice repair anyway, and I just love your Scottish accent.

Hi. What type/model are those thin brown coax cables? Are they 50 Ohms? Thank you.

Not surprised by so many damaged transistors, that is what happens in DC coupled stages. One transistor dies, but it takes out several others with it.

Beautiful equipment and a joy to watch. How do you manage not to drool constantly when seated happily between all that marvelous gear?

Nice one pico amps, counting the coulombs passing by are you haha. Nice device, I enjoyed it a lot

I ran across a Keithley 480 Picoammeter years ago a repaired it. It’s surprising accurate even compared to some high end modern equipment and beats out the mid range equipment. Also it look neat on the bench. I was able to find the manual that included parts list and schematic for it.

Still to do: The 225, 486 and 440 need to be run for a while before further CAL/evaluation etc. The 486 needs a triax connector which I don't have yet. Possibly replace the potentiometers inside the 440 with a small round Pcb (sympathetic design) on which I can fit 10-turn pots. 440: Update: So my replacement darlington pair transistors arrived (new old stock apparently!) so I switched out that TIP126 I fitted, also the amplifier transistor Q113.......WOW! the tempco on those old transistors is pretty bad. -15v rail was -14.5v at power up and slowly crept up......heat from soldering! Seems stable at -15v now though. Oh yeah, and the main darlington transistor that was fitted to the 440 when I got it......was a BFY51, an NPN transistor....ouch!

Very interesting pA stuff repair.. thank you - very satisfying. Didn't you check the zero baseline, i.e. possible bias or leakage currents of the different instruments? That might have been another source of error .. and maybe have been necessary before the F.S. calibration? Interesting to see one of the later successors of the 440 pico ammeter. Keithley as well has a systematic numbering system, like HP. 2xx for current source, 4xx for pico meters.

That Q112 was build in a a safety device, a current limiter only if things go wrong. That must have saved a lot of hardware with this fault. Or it could be that there already was no more regulation from te Darlington, but... the negative voltage was more than it should be. Nice straight forward repair 😎

Apologies if you addressed this (still watching the video) but what is the real-world use case for a device like this?

Excellent work Ian! I’m glad you were able to put my 440 to some use, repair and cal the picoamp range. +share the Nixie display for others to appreciate. Keep up the good work! Dan

Love those Nixie valves, it makes me wish I had a use for measuring Picoamps. Not too much call for it in Valve radio repair.

I REALLY love to see the engineering of old devices. Clever stuff! 👍

Excellent video; thank you sir.

Hi Ian, Awful lot of work to calibrate something you will probably never use! I can't think of a single case when I would need to accurately supply or measure nano-amps. Bob

Those old ceramic case transistors were always a mystery, some batches would fail fast because of contamination, and some would not. But well done to getting it right. The power supply having slightly different resistor values depends on the actual long tailed pair in use, if you had a batch with low gain you needed the changed value to sort of compensate for the base current, but if they had high gain (later production where the high gain bin was generally the most common bin, so the lower gain bands and the unbanded could be anything including high gain) then using identical resistors ensured a very close match in tracking between the rails. that would have been a part selected on production, where the transistors were gain checked, and then a decision made if the run needed to have the changed resistor to get the rails within tolerance, or they were selected in production and made up into packs accordingly, for the assembly line to use. Auto insertion machines and reels of assorted axial components were common, and there were a few who used a single reel, and your component was different as you went down, but an auto inserter would always place them in the same order.

Ian. Nice work - what's the burden voltage like on the picoamp range?

Hey thanks for the video. I'm about to tear into an E3634a and this was a great intro to what lies ahead. One question, why did you only replace the X2 RIFA cap? Why not the two smaller 1000pf across each side to ground? I believe these are Y2 so they never go short and shock anyone who grabs the case.

I. S. J. Gettin ‘er done!

The front panel design and even moulding of the handle are very Tektronix-like, haha! Nice beginner scope, plenty of life in it I'm sure.

Brilliant! Thanks.

For a "cheap" scope, it is remarkably well made. Would have been a shame to scrap it, but the question is will anyone now use it??

It's always capacitors...LOL. Another great video Ian.

Chinese caps in an expensive bit of kit - fantastic. Still, you replaced them with Jackcons so order us resumed 😂

Nice easy one this time - still fun to watch! =D

That really was an easy fix. The scope came from the UK Ministry of Defence, who probably had it on a shelf for 20 years before auctioning off, hence the lack dust. When I brought that scope, I brought several others of a similar vintage that were in equally good condition.

Only simple problem worth the effort to repair these scopes. A new one is only US $200!

An easy one! OK, who else saw right away the classic pattern of AC Humm when Ian first tried the digital store? 👍

Bravissimo

Nice to have a simple repair on such a complicated piece of equipment. Thanks for sharing.

11:50 the scope triggered on the junk signal when you plugged in your signal. "Reset" just resets the trigger, waiting for another one. You should have more subscribers, all your videos are so well done!

Had a Tek 2232, and yes the digital board decided to die, dead capacitor, a shorted Tek favourite, tantalum bead across the 5V rail. As I needed the scope that day, just unplugged the digital board, losing the ability to store, and the nice readouts, but the analogue side was still perfectly functional, so I finished the job, then sent it in for repair.

@5:00 caps at the bottom left are bulging… it’s always a crapacitor

I was surprised to see no numerical values on the CRT, goes to show the low cost. Always a stunner Ian *Cheers*

Ian, you are NOT in Munich, tonight? Shame on you. The Scots may show the Germans, how to play soccer..

Hey Ian im looking for replacement switch for my LT30/2 left switch with LED has seen better days any idea where i might get a replacement

I had an intensity pot problem with my old 422 from about 1968. It would hop from too low to too high. I couldn't find an exact replacement. I took it apart and found a dried blob of grease stuck to the wiping surface. Removed it and all is well. Not sure it deoxit would have helped there.

What an extremely kind gesture from Richard and I am so sorry to hear of his poor health. It's a great collection of parts and test gear probably amassed over decades, and it has gone to an excellent new home indeed.