Electronics > Repair

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

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abnormalalien:
Ok then! I think I might see the (a?) problem: the output of my U403 is not 7V, it's around 5.7V. However, I noticed as well that the -15V inputs to U403 is also not correct(-14.4V). If I'm understanding right, that comes from CR402A. So, if I replace CR402 and it properly outputs -15V, will U403 give me the correct 7V? Or are these two separately problematic components?

Zucca:
U400-A needs also a funeral in my eyes... the output should go 15V and not 6.35V.

Regarding the -15V being so high -14.4 remember it could also be too much current on the innocent CR402A.
You could also desolder CR402A and test it outisde....

My next steps would be:

1) Search for hot spots on the board... as I said before too much current can offset the power supply voltages.
2) Remove U400 and check voltages again
3) Remove U201 and check voltages again

There is not too much to measure further, grab the iron ehm... hot air gun and act.

BTW something does not make sense, PIN 1 U403 is 5.67V but PIN 3 U400-A is 5.90V unfortunately they should be connected and have the same voltage...  :scared: is that voltage changing in time? Time for getting a scope?

PS: Congratulations for your work, I wish all the beginners would be like you!  :clap:

Z

Dr. Frank:
U201 is defective, because it doesn't regulate the constant current through the 28.75k hybrid resistor correctly, and its offset between + and - is way too high.
U400-A is defective, as it does not amplify correctly to 10V, (and its offset is way too high, also), which in turn doesn't feed enough current to the LM399, its output is probably oscillating.
So the -10REF voltage of -6.13V might differ that much from the +10REF value of 6.35V, due to the oscillation also, but U401-A might as well be defective.
This can be decided only after replacement of U400, when the +10REF is ok again.

You should order 3EA of the AD706.

This -14.4V supply voltage is probably ok, as the value of CR402-A and also CR401-A  probably have been changed to 3.6V at some time.
Take notice, that the +15V supply is ALSO about 3.7V lower than these 18.73V, instead of the nominal 3.3V zener voltage.

Frank

abnormalalien:
Thanks you guys! I'm trying really hard on this one. One thing I'm a bit perplexed on...how do you mean is anything getting hot? Uhmm, I'm not real comfortable sticking my hands in there and that's about as hand-waving an estimation as I could make...is there some professional way of telling what the component temperatures are? Like an IR camera or something?

Zucca:
If you don't know where to put your fingers just don't do it.
Order some AD706s and start replace the failed components, we will see what happen then.

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