Author Topic: HP 3478A replacement transformer?  (Read 984 times)

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Offline The BootloaderTopic starter

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HP 3478A replacement transformer?
« on: January 10, 2023, 09:55:49 am »
Hi!

I just got a 3478A. Unfortunately due to improper packaging, the transformer pins were damaged during shipping, beyond repair (a shock snapped all the pins off the transformer, cutting the transformer wire directly at the windings, and breaking the plastic isolation around the core too)

So I am looking for a new HP 9100-4201 transformer...

It's a long shot but would anyone happen to have one in their parts bin, maybe from a parts unit? I don't expect these transformers to fail often so I am hopeful there are extras laying around.

Failing that, I would need to replace it. Seems like the analog windings are +-12V and +-24V and the digital one is +-12V per this post and it makes sense looking at the schematics.

I am having difficulties finding replacements with -24 -12 0 +12 +24 windings, let alone with an extra -12 0 +12 winding. Even -24 -12 0 +12 +24 is hard to find.
I could use 3 different transformers, worst come to worst, but if I can avoid that it would be great

Thanks for any pointer!
« Last Edit: January 10, 2023, 10:06:40 am by The Bootloader »
 

Offline Kleinstein

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Re: HP 3478A replacement transformer?
« Reply #1 on: January 10, 2023, 01:20:14 pm »
For the transformer it is not only about getting the voltages right, but also getting good isolation and shielding for the analog part. A seprate transformer for the digital / display part is not a problem.
The hard part if the analog part, as this really should have shielding.
 


Offline precaud

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Re: HP 3478A replacement transformer?
« Reply #3 on: January 10, 2023, 04:44:05 pm »
I have a spare 9100-4201, PM me if interested.
 

Offline The BootloaderTopic starter

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Re: HP 3478A replacement transformer?
« Reply #4 on: January 10, 2023, 07:51:29 pm »
Looks like I'll be getting a transformer! Thanks

Leaving the topic open in case someone has a magic suggestion for anyone else who might be facing a similar issue
 

Offline The BootloaderTopic starter

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Re: HP 3478A replacement transformer?
« Reply #5 on: January 12, 2023, 01:46:53 am »
Side note, if someone with a 3478A finds this topic because they are working on their 3478A.

There are 4 yellow RIFA capacitors on the 3478A. It is extremely likely that they need to be replaced, as by now due to age the original caps are likely cracked and unsafe. In my multimeter, the 4 of them were in very bad shape.

2 are located below the power switch (I recommend removing it for easier access), and 2 smaller ones are located near the rear panel.

For more info search the forum for "RIFA capacitors"
 
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