Data Precision 2480 DMM Repair

[singapol]

Try this, if you have a esr meter measure C38,39 if not swap C36,37 15uf 10V. I'll bet they have developed high esr. The caps are connected to 100V selector switch.

I will check them out. Though I believe those switches are basically four dual throw (changeover)  switches in one. I guess quad pole changeover... And the pins B1, B2, and B3 are all one of the four subswitches used for switching on the decimal place character on the display. When the switch is out B1 is connected to B2. When in B3 is connected to B2.

So I think those caps are isolated from the measurement circuit. But will check them out anyway. This thing is driving me nuts. Thanks.

The caps and switches are connected to voltage comaparator opamp Z5/ (.1REF) voltage reference and linked to R49 27K to a quantity symbol ( diameter1) back to AD convertor 48-4058? If it is not this then
check quantity ( diameter1) pin 13 of AD convertor signal chain.

[teksturi]

Try to measure voltage in different points. First put 5V in jacks and but DCV and 100V range. Then measure points
S6/A3 - S4/B1 = 5V
S2/B3 - A4/1   = 5V
A4/6   - A4/1   = 5V
A4/5   - A4/1   = 0,5V
A4/3   - A4/1   = 0,05V  (From your first post with fault it read about 0,0689V)
If there is something funky business (there should be) try different range and see those results.

You should also try wave the switches and see if that affects reading. That way you might see if switch is faulty or something.

I was also thinking that fault might be in switch S11 between A6-A5. If there is a leakage it will affect just 100V range but it should drop voltage not raise it.

[FlyingHacker]

The caps and switches are connected to voltage comaparator opamp Z5/ (.1REF) voltage reference and linked to R49 27K to a quantity symbol ( diameter1) back to AD convertor 48-4058? If it is not this then
check quantity ( diameter1) pin 13 of AD convertor signal chain.

Wow. I missed that! It is amazing what your brain does when you think you understand something. It prunes it away for efficiency. But when you really don't it bites you in the rear...

I will definitely check those out. Thanks.

[FlyingHacker]

Try to measure voltage in different points. First put 5V in jacks and but DCV and 100V range. Then measure points
S6/A3 - S4/B1 = 5V
S2/B3 - A4/1   = 5V
A4/6   - A4/1   = 5V
A4/5   - A4/1   = 0,5V
A4/3   - A4/1   = 0,05V  (From your first post with fault it read about 0,0689V)
If there is something funky business (there should be) try different range and see those results.

You should also try wave the switches and see if that affects reading. That way you might see if switch is faulty or something.

I was also thinking that fault might be in switch S11 between A6-A5. If there is a leakage it will affect just 100V range but it should drop voltage not raise it.

I have been doing that without figuring out why I am getting the readings I am getting.

What do you mean by "wave the switches" ?? You mean swap two of them? Or shift them all down or something? I have to figure out to remove the mechanical interlock (not that hard), and then I can remove them with a desoldering station.

Thanks.

[teksturi]

I mean that when you get wrong reading you touch switches and see if that affect that reading. Like shake or wiggle. I do not know how to say that more clearly. (Sorry my english of course)

Every measurement you make you can take those in the paper and post those in here. That way we get more info and it is easier find the fault. It is very difficult say were the fault is if we not know those measurements.

[tec5c]

Try to measure voltage in different points. First put 5V in jacks and but DCV and 100V range. Then measure points

Agreed. If you can poke around inside with the unit on then the best thing to do is to follow the voltage you're putting in. I mean, put 5v in then measure the voltage at the first point of contact to the PCB, then systematically trace the voltage through until you find the voltage drop...