Electronics > Repair
[SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621
Andrejka:
Hello colleagues
Can someone suggest me, what components to check if:
Self test shows errors: 612, 613, 615, 617, 618, 619, 621, 622
Ohm current source is working - I got correct 500nA, 5uA, 10uA, 100uA and 1mA
Only DCI mode seems to working correctly, on other modes only chaotic readings.
Comparing to other meter there is no input impedance (infinite input impedance reading). In working meter on DCV mode I can measure 10Mhom input impedance.
If Ohms current source is working then custom resistor assembly is ok?
Thanks
Andrej
TAMHAN:
Likely one of the SMD inductors close to the input jacks. They, um "levitate away" during shipping and handling. Sadly, I lost mine...and getting that Gowanda part is difficult. Which is why I currently dont have a working 34401A...but it is very low on the repair priority list.
Andrejka:
--- Quote from: TAMHAN on April 04, 2018, 08:19:45 pm ---Likely one of the SMD inductors close to the input jacks. They, um "levitate away" during shipping and handling. Sadly, I lost mine...and getting that Gowanda part is difficult. Which is why I currently dont have a working 34401A...but it is very low on the repair priority list.
--- End quote ---
Tamhan You are 100% right - cracked small inductor. Absolutely invisible with naked eye, but signal path tracing helps. Now looking for suitable replacement...
Thanks
Andrej
Resonant:
HP 34401a repair
I recently acquired a nice HP34401a, an early one made in the USA and I thought I would do some checks against my calibrated meter and left it on for a while, tried various voltages and they were close but generally a little high. This meter had been in private ownership and had very little use and probably not been calibrated since new.
After trying various voltages and putting the meter through its paces it came up with an error. So I re-ran the Test All which had passed OK earlier and it came back with the 612, 613, 615, 617, 618, 619 error codes. A quick scan on the net brought me to this thread where my heart sank when I read of all the possibilities and expense this could be.
I ran a few tests Voltages above 100V DC were Ok all AC ranges worked and there was still output current for the ohms readings although there were no readings. I tried the input impedance on most ranges it was the expected 10M ohm but on 100mV 1V and 10V it was only 66K so out with the circuit diagram of the input circuit.
It was late so I pondered it overnight and thought there must be a leak/short on the input. Looking at the resistor ladder R104 to R109 6X 13K looked close to the value I was getting so I checked C100 470p and sure enough it measured 1 ohm, so I lifted one end and ran the self-test and it passed again all OK, so I will be ordering a cap and checking out the resistors. I will post again when completed. I assume the cap is a filter to remove noise on the input along with C101.
A request, I was intending to calibrate it but the manuals explanation makes it look complex compared with a Keithley 2000 which I have done previously I found after entering parameter step 5 pressing Auto/Man exited calibration, so how do you move on to the next value without exiting?
Chris
HighVoltage:
Nice that you found the problem.
Some 34401A also suffer from blown tantalum capacitors.
When I have repaired these DMM, I replaced all of them.
If you do manual calibration, you have to do it for each value separately.
There is no next "value"
There is one "shortcut". Instead of pressing SHIFT and MENU ON/OFF just press SHIFT RECALL and it brings you back to the calibration menu.
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