Need help repairing a Keithley 2182

[droffsite]

I recently acquired an inoperative 2182 nanovoltmeter for the princely sum of nothing, hoping to get it back in shape. This will be my first time working on something this complex (previously fixed a PB-503 for grins).

On power up, all display segments light up nicely, then it shows REV:A06 A02. That's it for the good.

It then goes to OVR.FLW V with a rapidly flickering period off to the far right.

I opened it up and took a look: everything looks good (all the caps look brand new with no apparent leakage).

I've gone through the repair manual trouble shooting steps (page 4-11 in the service manual).

Step	Item/component	Required condition	Remarks	Result	%
4	U304, pin 2	+5V ±5%	+5VD, referenced to TP301	5.012	0.20%
5	U305, pin 2	+37V ±5%	+37V, referenced to TP301	36.35	-1.80%
6	CR313 anode	-6V ±20%	-6VD, referenced to TP301	-7.59	26.50%
7	Q304, pin 2	-5V, ±5%	-5VD, referenced to TP301	-7.64	52.80%
8	U302, pin 3	+15V ±5%	+15V, referenced to TP303	15.15	1.00%
9	U303, pin 3	-15V ±5%	-15V, referenced to TP303	-15.77	5.10%
10	U301, pin 3	+5V ±5%	+5V, referenced to TP303	4.99	-0.20%
11	CR305 cathode	+29V ±20%	+29V, referenced to TP303	31.49	8.60%
12	CR309 anode	-29V ±20%	-29V, referenced to TP303	-8.88	-69.40%
13	CR310 V+, pin 1	+18V ±20%	+18V, referenced to TP303	21.17	17.60%
14	CR310 V-, pin 2	-18V ±20%	-18V, referenced to TP303	-20.75	15.30%
15	CR306 anode	-7V ±20%	-7V, reference to TP303	-9.57	36.70%
16	CR308 cathode	+7V ±5%	+7V, referenced to TP303	7.87	12.40%

So clearly something's off, particularly on the negative side. I replaced Q304 (ordered several of each of the out-of-spec parts) to no avail, then thought I might be getting ahead of myself.

I'd like to validate that the transformer is good, but I can't find any specs on what the secondaries should be.

Any inputs, guidance, donations, well-wishes... whatever would be more than welcome.

[chekhov]

Check out K2000/K2010 repair threads, transformer is the same at least.

Sorry, transformer is different for analog section, it seems I fooled myself long time ago, only now realized it's the same for K2000/K2010, but K2182/K2182A has indeed different one.
* Service manual for K2182 says it's TR-299B, but teardown pictures clearly say TR-372.

[Kleinstein]

I would not expect the transformer to be faulty. They are relatively robust and often postive and negative voltages are driven from the same winding.
It looks like the regulator for the -5 V is somewhat broken.

The -29 V look like there is something really pulling it down, a open diode (rare) or maybe a bad / not connected capacitor.

[droffsite]

Thanks for the reply!

Service manual for K2182 says it's TR-299B, but teardown pictures clearly say TR-372.

Interesting. Mine has a TR-299B. I meant to post the voltages first time.

4 pin connector:
Brown: 97 V
Brown: 92 V
Yellow: 83 V
Yellow: 64 V

5 pin connector:
Green: 1.5 V
Green: 3.0 V
Orange: 3.4 V
Orange: 5.9 V
Purple with red stripe: 1.7 V

[droffsite]

It looks like the regulator for the -5 V is somewhat broken.

I ordered several new voltage regulators; I'll see about putting one of those in.

The -29 V look like there is something really pulling it down, a open diode (rare) or maybe a bad / not connected capacitor.

Another good thing to check.

Thanks!

[chekhov]

Interesting. Mine has a TR-299B. I meant to post the voltages first time.

That's seem to be a good piece of news for me.

Btw, regarding transformer voltages, they look a bit odd, and not sure how it was measured.

Here is what it looks like in K2000.
Volts AC were measured between transformer outputs (disconnected and in place):
                 No load      Load
4-pin connector
brown-brown        ~8.8      ~8.0
yellow-yellow     ~42.3     ~39.6

5-pin connector
green-green        ~9.8      ~9.2
gray-orange1      ~21.1     ~19.7
gray-orange2      ~21.1     ~19.6

[droffsite]

Btw, regarding transformer voltages, they look a bit odd, and not sure how it was measured.

That is not how I measured them (wasn't sure the correct way). I checked each wire to ground. Let's try that again...

Volts AC were measured between transformer outputs (disconnected and in place):
                 No load      Load
4-pin connector
brown-brown        ~8.5      ~7.7
yellow-yellow     ~42.7     ~38.9

5-pin connector
green-green        ~9.2      ~8.4
gray-orange1      ~18.9     ~17.3
gray-orange2      ~18.9     ~17.2

[chekhov]

Voltages look pretty decent at least to me.

Ah, the main question I wanted to ask as soon as I read first message. It goes OVR.FLW, but when you short the inputs (of first, of second channel, depends on selected one), what do you get, and anyway you haven't told anything about an attempt to measure something. Just to make clear whether meter reads anything at all or not, how close it to the expectations ...

[droffsite]

Voltages look pretty decent at least to me.

One bit of good news for me!

Just to make clear whether meter reads anything at all or not, how close it to the expectations ...

Oh, that little detail. Yeah, should've mentioned: either set of inputs, any range, no reading, just overflow.

[dietert1]

I am looking for a schematic of the Keithley 2182A power supply.
There is an inconsistency with the service manual, where they show the isolated supply has 15V, -15V and +5 regulators. But the reference pin of the -15V seems to be with a red LED to Gnd, so there is an extra 1.6 V or so, in total -16,8 V measured instead of -15 V.
A lapse may have happened when they renamed the 2182 service manual to 2182/2182A service manual.

Regards, Dieter