Keithley 2010 Repair

[KungFuJosh]

U139 LT1124CS8:

1: 0
2: -15.8V
3: +6.2V
4: +6.2V
5: 0 (unstable)
6: +15.146V
7: -5.936V
8: 0

The voltages look OK.

A 7 V reference level would come from the LM399.

6.9V at the ref. But those U139 voltages are not okay. 0 at 5 is wrong, and maybe inconsistent. See my updated voltages and comparison to picburner's good voltages:

Measurements on U139 (on for 10 minutes, input shorted, DC Volt)

1: 0.000
2: -15.799
3: +6.437
4: +6.437
5: +7.374
6: +15.174
7: -7.439
8: 0.000

Thanks!

U139 LT1124CS8 (on for 10 minutes, input shorted, DC Volt):

1: -0.3mV
2: -15.8V
3: +6.2V
4: +6.2V
5: +6.86869V
6: +15.16V
7: -5.93V
8: -0.4mV

The supply voltages are correct, but the output voltages are not.

[Kleinstein]

I quoted the wrong old answer: the unstable / 0 V at pin 5 was the initial measurement, likely with a contact problem at the probe.  A later reading at that voltage was stable and an OK voltage. The exact voltage at pin 5 does not really matter and it depends on the low grade zener VR113 that can have large tolearance (e.g. anything from some 3 V to some 25 V could work).

The point to check would be if the ADC actally gets the 6.9 V at TP105. during the test 101.2.

[KungFuJosh]

Thanks, I'll check that when I get home.

[KungFuJosh]

The point to check would be if the ADC actally gets the 6.9 V at TP105. during the test 101.2.

As expected (fail 101.2), it does not get the correct voltage. The peak voltage seen there was 4.4V.

Thanks,
Josh

[Kleinstein]

According to the plan there is only the DG408 mux (U163) between the 7 V reference (LM399) and the main amplifier. As other functions seem to work, it would be odd that the DG408 is bad only at one pin.  Maybe check the 7 V all the way to the chip (pin 12 in the plan). Maybe there is a broken trace, bad via or bad solder joint. Maybe resolder pin 12.

If most other functions work, I doubt that the digital control signals (pins 1,2, 15,16) are the issue.

[KungFuJosh]

Measurements on U139 (on for 10 minutes, input shorted, DC Volt)

1: 0.000
2: -15.799
3: +6.437
4: +6.437
5: +7.374
6: +15.174
7: -7.439
8: 0.000

Could you please also share your voltages from R271?

Thanks!
Josh

[KungFuJosh]

According to the plan there is only the DG408 mux (U163) between the 7 V reference (LM399) and the main amplifier. As other functions seem to work, it would be odd that the DG408 is bad only at one pin.  Maybe check the 7 V all the way to the chip (pin 12 in the plan). Maybe there is a broken trace, bad via or bad solder joint. Maybe resolder pin 12.

I see what you're looking at, but your description confuses me. On that side, U141 out goes to U163 to U130 to U176 before we get to TP105. U141 ref out also goes to U139 to R271 (with R300 on one side) to TP105. Or am I reading that wrong?

From other threads with people having 101.2 fails- R271 and U139 came up as a problem for different people. R271 on this is repaired now, which solved 400.2, but had no effect on 101.2. Since replacing R271 worked for others with 101.2 fails, it seems logical to follow that path as well.

I would like to compare R271 voltages to a working unit to see whether or not that path is relevant.

Either way, I'll resolder pin 12 on U163 because I would love a ridiculously simple fix if that's it.   ...ETA: no effect.

Thanks,
Josh

[KungFuJosh]

Here's a couple photos from that section. I had the cover on in the previous photos.

Thanks,
Josh

[Kleinstein]

The driving side for TP105 is from U177 that is the ouput for the main amplifier with Q192 / Q194 JFETs as inputs.

So the signal path towards TP105 is from U163 pin 8  and sometimes also via U176 pin 3 -switched to pin 2.
U163 is the main input MUX to choose the signal to the signal to the main amplifier.
The signal than goes through R370 to Q194.
The path to R271 (the TF245 array) is the input to the ADC. In the K2000 R271 would also provide the divider for the cases with gain.
It looks like the K2010 uses separate resistors (R428,R429,R431) for the gain settings and U176 to choose the gain.
I think there is still something worng with the plan around U176 and the gain switching: pin 10 and 15 should be connected to pin 7 and likely not Q184.
The connection of C269 also looks odd.

U130 the shift register and provides the digital control outputs.

[KungFuJosh]

I verified the schematic, and those points you mentioned are all correct. There is 32Ω between U176 10+15 to 7. 10+15 do connect to Q184. C269 is also correct. I found no errors in that section so far.

U163 p8 connects to U176 p3. I suppose I should check voltages on both those chips anyway.

Thanks,
Josh

[picburner]

Here I am. Measurements on R271:

1 = 12.875V
2 = 6.437V
3 = -12.871V
4 = 12.875V
5 = -12.871V
6 = 0.000V
7 = 0.000V
8 = 0.000V
9 = 0.000V
10= There's a signal at this pin, I should measure it with an oscilloscope.
11= -0.0246V
12= 0.002V
13= 0.0256V
14= -42834V
15= 0.000V
16= 12.232V

[KungFuJosh]

Here I am. Measurements on R271:

Thanks!

I retested R271, and they were close enough to the original that I won't bother reentering them.
R271 TF-245:
1: +12.4207
2: +6.21061
3: -12.4196
4: +12.4208
5: -12.4193
10: (see attached)
13: -24.85mV
14: -4.1384
16: +11.7987
(6,7,8,9,15 at ~0V)

16 is the biggest difference, but also pointless since it's the small difference at p1 and p2, and p16 doesn't go anywhere.

Could you also please check the voltages at U163 and U176?

Thanks!
Josh

[KungFuJosh]

Here's what I got:
U163:
1: +4.97V (unstable)
2: +4.97885V
3: -15.8423V
4: +108.841mV
5: +1.000879V
6: +6.21053V
12: +6.92594V
13: +15.1556V
16: +4.97V (unstable)
(7,9,10,11,14 = 0V)
(8,15 unstable)

U176:
1: +4.97824V
4: -15.7222V
8: +4.97V (unstable)
9: +4.97V (unstable)
12: +4.97788V
13: +21.2277V
(2,5 = 0V)
(3,6,7,10,11,14,15,16 unstable)

The unstable +4.97 voltages ranged in 4.XX.
The other unstable voltages were probably within +/- 1V, and I assume maybe signal, but I didn't scope any of them.

Thanks,
Josh

[Cyclotron]

Here I go again. I have a K2010 inbound that's broken. I followed you down the frequency counter path, and now I will have one of these in the queue to get going. It will be welcomed to a home that has 2 K2001M and a K2002, so it will have good company. I'm told the one I purchased doesn't read voltage. I had a K2001 that was like that, and it had sustained major damage to the voltage-measuring circuitry.  Enough that I had to do some PCB epoxy repair to eliminate the carbon.

[KungFuJosh]

Here I go again. I have a K2010 inbound that's broken. I followed you down the frequency counter path, and now I will have one of these in the queue to get going. It will be welcomed to a home that has 2 K2001M and a K2002, so it will have good company. I'm told the one I purchased doesn't read voltage. I had a K2001 that was like that, and it had sustained major damage to the voltage-measuring circuitry.  Enough that I had to do some PCB epoxy repair to eliminate the carbon.

I know which meter you're referring to. I hope they gave you a good deal! ...and I hope it's an easy fix anyway.

[Cyclotron]

Here I go again. I have a K2010 inbound that's broken. I followed you down the frequency counter path, and now I will have one of these in the queue to get going. It will be welcomed to a home that has 2 K2001M and a K2002, so it will have good company. I'm told the one I purchased doesn't read voltage. I had a K2001 that was like that, and it had sustained major damage to the voltage-measuring circuitry.  Enough that I had to do some PCB epoxy repair to eliminate the carbon.

I know which meter you're referring to. I hope they gave you a good deal! ...and I hope it's an easy fix anyway.

I got it for considerably less than they were asking. I was surprised by how responsive they were to an offer. I had thrown an offer at another broken one, and it was flatly refused with no counteroffer.  I hope it's an easy fix too, but where's the fun in that?

[KungFuJosh]

I got it for considerably less than they were asking. I was surprised by how responsive they were to an offer. I had thrown an offer at another broken one, and it was flatly refused with no counteroffer.  I hope it's an easy fix too, but where's the fun in that?

Nice. Well, they were being picky about offers a month or two ago when I tried. I think they were more realistic by the time you contacted them.

Ok, I hope it's an enjoyably challenging fix.

[picburner]

Removing the black box the values ​​shown on the display changes, so I assume the measurements taken on the ICs also do.

U163:
1 = 5.0043V↓
2 = 5.0043V
3 = -15.816V
4 = 0.1094V
5 = 1.01064V
6 = 6.437V
7 = 0.000V
8 = Signal
9 = 0.000V
10=0.000V
11=0.000V
12= 7.028V
13= Signal
14= 0.0005V
15= Signal
16= 5.0043V↓

U176:

1 = 5.0043V
2 = 0.0012V
3 = Signal
4 = -15.816V
5 = 0.0005V
6 = Signal
7 = Signal
8 = Signal
9 = 5.0043V↓
10= Signal
11= Signal
12= 5.0043V
13= 21.231V
14= Signal
15= Signal
16= Signal

↓ means the voltage value drops to about 4.3V in several steps.

[Kleinstein]

The signals dropping from 5 V to some 4.3 V are digial control signals. So the controls send are changing. Those signals should be 0 V / 5 V with maybe variable timing.

The 7 V signal to the ADC seems to be measured not contineous, but in a sequence, like the normal AZ cycle (switch between 0 V (pin 9 of U163) and 7 V (pin 12 of U163)) . So it would need the scope to look at pin 8 of U163. TP105 should follow that signal with maybe some overshoot / ringing.

[KungFuJosh]

Removing the black box the values ​​shown on the display changes, so I assume the measurements taken on the ICs also do.

U163:
1 = 5.0043V↓
2 = 5.0043V
3 = -15.816V
4 = 0.1094V
5 = 1.01064V
6 = 6.437V
7 = 0.000V
8 = Signal
9 = 0.000V
10=0.000V
11=0.000V
12= 7.028V
13= Signal
14= 0.0005V
15= Signal
16= 5.0043V↓

U176:

1 = 5.0043V
2 = 0.0012V
3 = Signal
4 = -15.816V
5 = 0.0005V
6 = Signal
7 = Signal
8 = Signal
9 = 5.0043V↓
10= Signal
11= Signal
12= 5.0043V
13= 21.231V
14= Signal
15= Signal
16= Signal

↓ means the voltage value drops to about 4.3V in several steps.

Thanks for checking those!

U163 pin 13 should be V+, not signal. Can you please retest this?
U176 pins 8 and 9, same type on mine- are you sure they're not on yours (both on mine do the 4.3 to 5 thing)?

Thanks,
Josh

[picburner]

Yes, my mistake: U163 pin 13 = 15.173V
U176 pin 9: I confirm the reading.
Pin 8 varies between 4.9 and 4.5V.
I should use a scope for these signals, but I don't have space on the table for other instruments right now.
I'm keeping the K2010 open anyway...

[KungFuJosh]

U176 pin 9: I confirm the reading.

I'll have to retest mine also then. I wonder if this is a useful clue... 🤔

[Kleinstein]

PIn 9 of U176 should be used for switching to gain 10. The DG444 is active low and thus gain of 10 if pin 9 is low.
The question is how Tp105 and U163 pin 8 looks on the scope, when doing the failing self test step.
Depending on how pin 8 looks one would check pin 12 and maybe pin 2.

[KungFuJosh]

The question is how Tp105 and U163 pin 8 looks on the scope, when doing the failing self test step.
Depending on how pin 8 looks one would check pin 12 and maybe pin 2.

U163:
Pin 2 = CH1
Pin 8 = CH2
Pin 12 = CH3
TP105 = CH4

I can trigger on pin 8 or TP105, but nothing happens on pin 2 or pin 12 during the 101 test. If I should set this up another way or test something else, please let me know.

Thanks,
Josh

[Kleinstein]

The amplifier seems to somewhat work, but there is a huge offset and for some reason the voltage at the input is much smaller than it should be, like quite some current flowing. It looks  like there is something wrong with the amplifier (e.g. Q193, Q194, ...U173U177) or U173U176.
The part around Q184 still looks wrong in the plan. The link to U174 pin 3 makes no real sense. That pin should have a resistor to GND or maybe +15 V.

One could check the voltage over R370 - this should ideally be very small (sub µV range), in case of a fault could be up to 1 V or so.

One way for current flow could be via U173 U176from pin 3 to pin2. The switch should be off, but could be bad. The voltage at pin 2 could give a hint.

Pin 7 of U173 U177should be the other input of the main amplifier and should be identical to TP105 if things are correct.

ps: fixed chip mixup