Fluke 8842a Repair / help

[joerice01]

Hi all,

I recently purchased a fluke 8842a DMM for my bench.
After opening it up I saw that it looks like the copper is lifting off the optional boards.

I guess this is just due to It's age...

after testing all the inputs I discovered that the low VDC range seems to float after test.

If I test 5v the display reads 5v, then if I remove the probes the reading will stay at 5v and trickle down a little bit.
If I then short the probes the reading will return to 0.0v

this doesn't happen on the higher DC ranges, I can hear a relay switch over which leads me to believe there is a fault in the lower range circuit.

Luckily for me the 8842a manual has an extensive troubleshooting section, so will take some time this weekend to go through it and test.

Has anyone had an experience with this type of problem before?

Thanks for your help.

[2N3055]

That is not copper lifting.. That is solder.. It doesn't have galvanic tin protection, but copper was covered with solder.. It was quite common in that era..
In the lower DC ranges, meter has input impedance on order of many Giga Ohms. In order to check zero offset you need to short inputs...

So those two are not problems...


Regards,
Sinisa

[joerice01]

Sinisa,

Thanks for sharing your knowledge with me.

I don't have a lot of experience with gear from this era...

Thanks again.

[mzacharias]

Hi all,

I recently purchased a fluke 8842a DMM for my bench.
After opening it up I saw that it looks like the copper is lifting off the optional boards.

I guess this is just due to It's age...

after testing all the inputs I discovered that the low VDC range seems to float after test.

If I test 5v the display reads 5v, then if I remove the probes the reading will stay at 5v and trickle down a little bit.
If I then short the probes the reading will return to 0.0v

this doesn't happen on the higher DC ranges, I can hear a relay switch over which leads me to believe there is a fault in the lower range circuit.

Luckily for me the 8842a manual has an extensive troubleshooting section, so will take some time this weekend to go through it and test.

Has anyone had an experience with this type of problem before?

Thanks for your help.

This is quite normal due to the extremely high (several Gig-Ohms) input impedance at the 20V range and below. Above that, at the 200V range for example, the input impedance is 10 meg and so even this internal resistive load will drain off the voltage reading once the probes are removed from the voltage source.

This question comes up fairly often.