HP 400F AC voltmeter

[vecher]

My ac voltmeter will not zero any more .., Anyone have a manual or schematic for it? Or what do I check.. It was working but lately it will not zero on any scale The lower the scale the worst..

Thanks'
Skip

 

[FuZZ1L0G1C]

Is it a panel meter?
Might be that needle has bent from 'pinning'.
Or plastic zero-cam may be worn or cam-pin broken.

 

[dorke]

Welcome to EP.
Here is the operation and service manual of the HP 400F/FL.
Are you able to get mechanical zero?

 

[73's de Edd]

Sir Skip . . . . .

INITIALLY . . . . . with no power applied, check to see where your meters mechanical pointer setting is having
the meter pointer being positioned, as relevant as to how close it is initially being, to scale ZERO.
Then check out the meter amp and bridge circuitry for its +- 26V's supplies and derived -6 and 9V supplies.
Also check out how well and balanced the YELLOW squared electrolytics are holding up after being 50 years old.
This was a military / aerospace microfiche schematic, so I further magged it up enough to make every small
component marking readable.
Certainly beats the service manuals piecemeal schematic sheets, if you have to travel across sections.

Re . . . .REFERENCING:

73's de Edd

 

[vecher]

Welcome to EP.
Here is the operation and service manual of the HP 400F/FL.
Are you able to get mechanical zero?

Yes

As I go down in ranges the meter reads higher.. Does not maintain 0 Even at highest ranfe metrr is still not at 0 but pretty close.. This is with no input and terminals not shorted together..

Skip...

 

[dorke]

You do need to short the input terminals together, i.e. Vin=0,
the lower the input range the more important that is!
Do that with the shortest possible wire.
Still no zero?

 

[(*steve*)]

I recommend you check A2Q15, A2Q16, A2Q17, A2C38, A2C39, and A2C40.

These are the components commonly associated with a meter deflection with no input.

Edit: Edd has already suggested looking at those caps.

 

[vecher]

I recommend you check A2Q15, A2Q16, A2Q17, A2C38, A2C39, and A2C40.

These are the components commonly associated with a meter deflection with no input.

Edit: Edd has already suggested looking at those caps.

Ok I will check tomorrow.. Thanks

Skip...