Author Topic: Restoration glory of Keithley 2001 DMM  (Read 203446 times)

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Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #750 on: March 31, 2019, 03:14:17 am »
Does anyone have a thermal image of their analog board ?

My 2001 notes article have plenty of IR photos on 2001. They do like to get bit toasty  ^-^.
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Offline Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #751 on: March 31, 2019, 09:07:28 am »
Does anyone have a thermal image of their analog board ?
My 2001 notes article have plenty of IR photos on 2001. They do like to get bit toasty  ^-^.
No wonder the caps were toast.
Too bad the caps leak instead of dry up. :)
 

Offline eplpwr

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Line sync sketchy
« Reply #752 on: April 15, 2019, 07:10:01 am »
Hi!

Recently I got a 2001 in good condition. The meter works great, except for one thing: When I enable Line Syncronization (followed by TRIG button) the display updates become sketchy and for long times the display just shows "---------" [VDC/ADC/Ohms/whatever]. So, it seems there is at problem with the mains zero-crossing detection (or whatever method is used to sync to mains). The L-S problem was present when I received the meter, but I have no complaints as it was really cheap - sold as Parts.

This is what I've done to the meter, after receiving it:
- Replaced all electrolytic capacitors on both analog and digital board. The "old" ones had 2008 datecodes and did not show any signs of leaking.
- Upgraded firmware to B17/2001M. Unit was received with B16 firmware (now uploaded to xdevs.com).
- Upgraded from plain SRAM (no MEM option) to MEM2 (DS1245Y). Initialized NVRAM from Secret menu - working good.

I have the Repair manuals, complete with schematics, but I have trouble understanding which net is used for Line Sync.

Self-test passes all tests with no errors.

Is there some obvious solution to my problem that I've overlooked?
 
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Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #753 on: April 15, 2019, 11:57:49 am »
Thanks for firmware!

Does your unit pass all self-test in continuous loop  for few hours? Sometimes there is random error due to bad optocouplers between analog/digital, that cause "locks/freezes" like you describe.
What if you gently smack unit on the side, do the readings change (freeze up/reset/etc)? Line sync is FREQ signal that goes into A/D board, so you can trace from there.

Pics would be nice to see, sounds like your meter rather recent.
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Offline eplpwr

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Re: Restoration glory of Keithley 2001 DMM
« Reply #754 on: April 15, 2019, 08:34:37 pm »
Does your unit pass all self-test in continuous loop  for few hours? Sometimes there is random error due to bad optocouplers between analog/digital, that cause "locks/freezes" like you describe.
What if you gently smack unit on the side, do the readings change (freeze up/reset/etc)? Line sync is FREQ signal that goes into A/D board, so you can trace from there.

Pics would be nice to see, sounds like your meter rather recent.

Hi TiN!

It seems I can run self-test for several hours without any errors. I didn't think of "smacking" the unit, but after trying that there is definitely somethings going on: after enabling line sync, I get a reading every 10-15 seconds (conversion speed "normal" - default). Between the readings "---------" is shown in display. If I bump the meter (not too hard  :D ) I can unfreeze the meter to get a few readings before meter goes back to "--------" display. So my "average # of readings per minute" goes up when bumping the meter. Something electro-mechanical seems to be going on - just have to figure out exactly what's happening.

An observation: When changing to Line Sync, there is always a number of initial readings for 2-4s after pressing the TRIG button. It's almost like some capacitor was fully charged and then drained of energy, only to be recharged each 10-15s to get a few more readings, before being emptied of charge, again. This is a long shot, I know...

I have to disassemble to meter again to be able to probe the connectors to the A/D board - FREQ specifically.
 

Offline openloop

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Re: Restoration glory of Keithley 2001 DMM
« Reply #755 on: April 15, 2019, 10:23:44 pm »
Looking at the schematics, it appears that the main CPU gets its line readings straight from main power transformer taps. Digital board's U628 (page 2 of addendum part 2) is a comparator which detects zero crossings and feeds them straight into the CPU (pin 56)   
 
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