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HP 3478A Transformer Winding

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salvodi89:
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!

ddavidebor:
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?

salvodi89:
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

madshaman:
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!

alm:
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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