Electronics > Repair

[SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621

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Dr. Frank:

--- Quote from: bitseeker on July 02, 2021, 05:52:20 pm ---Thanks for including the analysis schematic, Frank. My 34970 just needs a new battery, but I'll know where to come back to if it misbehaves beyond that.

--- End quote ---
No problem.
Nobody asked about the T-sensor, so far.
Frank

JohnAH:
Hello Gentlemen,
  Thank for all the great information about the Hp34401 errors 612, 613, 615, 617, 619 ect. But so far none of the solutions have solved my meter's failure.
Hoping you can help me or at least point me in the right direction. 

I have swapped out U201, q201, and q202. Looked for shorts and opens but have found nothing out of order. I have a good meter to compare it to but still can't seem to figure it out. Attached is Dr Frank's Current Source sheet with my values in blue. 

Thanks for any light you can shed on the problem.

John

Dr. Frank:

--- Quote from: JohnAH on August 04, 2021, 03:16:15 pm ---Hello Gentlemen,
  Thank for all the great information about the Hp34401 errors 612, 613, 615, 617, 619 ect. But so far none of the solutions have solved my meter's failure.
Hoping you can help me or at least point me in the right direction. 

I have swapped out U201, q201, and q202. Looked for shorts and opens but have found nothing out of order. I have a good meter to compare it to but still can't seem to figure it out. Attached is Dr Frank's Current Source sheet with my values in blue. 

Thanks for any light you can shed on the problem.

John


--- End quote ---


John, your voltages are partly ok, if you compare it with the latest diagram I have published for my 34970A. The slight differences probably occur due to different supply voltages and a different zener diode.
It's not clear, what mode you use, and in which state you took the measurements.. i.e. open circuit in Ohm modes, or 4W, or which resistor was attached?

Which error messages do you get, when you are doing the full self test?

Please measure the constant current values e.g. in 4W mode out of the "Input Hi / Lo" jacks, for 100 Ohm to 10MOhm ranges.

Frank

JohnAH:
Error codes 612, 613, 615, 617, and 619
blue ink measurements were 2 wire ohms auto

4 wire in respective ranges against high accuracy resisters .1%
R            I             Range
100ohm .998mA    100 range
1k ohm  .998mA    1K range
1k         .o991 mA  10k range
1k         .0096 mA  100k range
80k       .0095mA   1M range
80k       .0046mA   10M range

The ohm readings were quite close. I didn't calculate them out but all probably within 1%.

Dr. Frank:

--- Quote from: JohnAH on August 04, 2021, 05:33:05 pm ---Error codes 612, 613, 615, 617, and 619
blue ink measurements were 2 wire ohms auto

4 wire in respective ranges against high accuracy resisters .1%
R            I             Range
100ohm .998mA    100 range
1k ohm  .998mA    1K range
1k         .o991 mA  10k range
1k         .0096 mA  100k range
80k       .0095mA   1M range
80k       .0046mA   10M range

The ohm readings were quite close. I didn't calculate them out but all probably within 1%.

--- End quote ---

1M and 10M ranges have the wrong currents, if you didn't mix up the ranges / measurements.. should be 5µA and 500nA instead of 10µA and 5 µA.. a pity that you can't measure the low currents with higher resolution.
Anyhow, this would partly explain errors 612, 613 but not the others, as these currents or compliance voltages seem to be ok.

Another question:
What have you done with Q201, Q202, U201:
Did you swap  them, i.e. really swap Q201 and Q202,  or have you replaced all 3 components with new, compatible ones?

Would it be possible for you to check all these ranges at near Full Scale, i.e with the appropriate resistors, like 10k, 100k, 1M and 10M?

Did your instrument fail, or have you bought it as defect?

The current sources seem to be work, maybe partly, but something is wrong at the output stage Q202 and behind.
Maybe the switches inside the ASIC are steered incorrectly...
I have to think a bit more, in the meantime.

Frank

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