HP 400FL AC Millivoltmeter

[oldsoul]

I have this unit in complete stock condition. The problem is randomly the needle will bounce all over the place or just stay at zero. Then if I tap on the case the needle will sometimes return to its measured value. Sometimes not.

[donlisms]

Have you done anything to try to find the problem?  Have you taken the covers off and poke at things with an insulated stick to try to see what part is most sensitive?

[oldsoul]

I did take the panes off. My mistake it does look like someone did replace a few of the electrolytic caps. The only thing I notice is if I move the wire going to the meter the meter jumps a little. When under test and the needle operating properly it will out of nowhere just go wild and often just bury down to 0

[jonpaul]

hello all the old classic analog meters suffer from paint and debris chips off the faces.

These enter the D'Arsonval movement and cause sticking and blocking.

Turn meter on its face, gently tap sides and see if it improves or changes.

Often the debris clogging will fall down to the face and can be see and removed.

I have many similar meters and never had to replace any lytics, the HP 197-0s..1990s were top quality.

Bon chance \


Jon

[Kosmic]

I would still check electrolytic capacitors. I had to change one in an erratic 400e.