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HP 3478A Transformer Winding

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Hello everyone!
I'm Salvatore from Italy and I'm new in the forum.
I bought an used HP 3478A multimeter from ebay and today it arrived... but... It doesn't work!
I think it's a problem with the transformer becouse when I try to measure the primary winding I get an Open Circuit!
Can anyone give me what he measure?
I need 220V winding...

Thanks everyone!

PS: The forum and the video are wonderful!

Ciao, domanda non scontata, hai misurato direttamente sul trasformatore o sei passato per i vari circuiti di filtraggio e protezione?

Hi, do you have measured right on the transformer or on somewhere else?

Yes! I measured directly on the transformer (I'm not so stupid  :-DMM).
Anyway there is no mouch filtering on the primary side of the transformer.

I can add more details...
- 46-50Ohm on the 100V tap (between 6-7 on primary side of the transformer).
- 50-55Ohm between 8-9
- Anywhere else open!  |O

Hi, funny story, I've also just purchased an HP 3478A from eBay that doesn't work and am trying to fix it :) (post in this topic).

I'm wondering what kind of failure would cause the primary to become an open circuit inside the transformer?

From what you're saying, between 7 and 8 you've got an open circuit (and I assume of course it's an open circuit between 6 and 9, which is what you want)?

One suggestion, but maybe not a smart one given there might be damage inside the transformer, is if you've got a variac, you could try to drive the 100V tap.  I'd probably try to remove the whole transformer to test it.  I hope I don't have a similar problem as there are a whack of secondary taps (looks like six).

I'm wondering how easy it would be to find a replacement for that transformer; doesn't look hopeful.  Personally I'd be loathe to operate anything from a transformer that looks like something bad happened inside.  If you're feeling brave you could always tear it apart and try to rewind it ^^'.

I'm going to try and video myself as I try to troubleshoot and repair mine, can't make any promises on how long that would take me to edit and post though.

Good luck!

Transformers often contain an internal thermal fuse. Not sure if this applies to the 3478A, but it's worth a shot. The fuse is usually user replaceable with some care.


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