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Old 2nd Aug 2020, 5:22 pm   #1
Humber888
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Default HP3325B Mains Input Filter

There I was using my HP3325B function generator to check out my newly acquired Tektronix current probe when the 3325B let out copious smoke. This smacks of the well known 'Schaffner mains filter with Rifa capacitors' problem. I can see the filter on the appropriate circuit diagram page of the service manual but I can't find it in the parts list.

Does anyone happen to know the type number of the filter/fuse/voltage selector fitted before I start dismantling the unit?

Many thanks.

Mike
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Old 2nd Aug 2020, 5:56 pm   #2
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Default Re: HP3325B Mains Input Filter

Bit newer than anything HP that I own, but it looks like a Schaffner unit, these have either paper based RIFA or WIMA caps inside, the free manual doesn't have any service info.
Picture from a youtube video, can't see the part number.
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David
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Old 2nd Aug 2020, 7:15 pm   #3
mhennessy
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Default Re: HP3325B Mains Input Filter

I've seen many different types used in HP gear. From a quick look, this picture suggests it's the same as the one I recently replaced in my 3314A:

https://www.woutersenwouters.be/site...3325B%20B1.jpg

But from recent discussions with another owner of an earlier 3314A, it appears that his model doesn't use that particular inlet. Long-running models get revised from time to time, naturally. So that picture is no guarantee your example will be the same.

But if yours is the same as the 3314A, the part number is FN370-2-22. Please note that there are many possibilities that look identical from the outside, so you really need to extract the old one and see what's printed on the label. This datasheet shows the variations on the FN370 theme:

https://www.schaffner.com/product-st...sheets/fn-370/

It's nice that replacements are still available. In the case of the half-width 3314A, it would have been tricky to bodge something else in place of it, and it's probably not exactly easy for the 3325B either if that picture is any indication. I found that RS didn't have exactly the right part, but had a promising alternative, but in the end I got mine from Mouser in the US.

Tip: when you get the old one out, keep the voltage selection cam, as it will have 220V and 240V markings on, whereas the new one comes with 230V and 240V.

Good luck,

Mark
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Old 3rd Aug 2020, 3:48 pm   #4
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Default Re: HP3325B Mains Input Filter

Yup, its definitely a Schaffner - would help if I noticed the name on the outside of the filter! I still need to identify the exact type as other things have conspired to stop me doing any more investigation at present. I also need to prove that the fault is caused by the filter itself. The service manual found on line has circuits and parts lists for just about everything except the filter. Mark I did see your really useful comments on the filter in the 3314A thread. Hopefully the 3325B uses the same model number - the outside certainly looks the same.
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Old 6th Aug 2020, 4:56 pm   #5
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Default Re: HP3325B Mains Input Filter

I've finally extracted the mains input filter. It was a right pain to do so. Yes it is a Schaffner FN370-2-22. So I'd better get hold of a new one from Mouser. Does anybody else need one for their kit while I'm putting an order together? I was also going to replace the filter in a Solartron 7150+ bench DMM but it uses an FN372-2-21 and these are out of stock at Mouser.
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Old 6th Aug 2020, 8:21 pm   #6
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Default Re: HP3325B Mains Input Filter

If only I'd known when I ordered mine

I had no problems getting to 33 for free delivery on that occasion, but yes, jobs often get bunged up for that reason. For what it's worth, I was very impressed with the service from Mouser - it was very quick to arrive, and no hassles at all.
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Old 6th Aug 2020, 9:36 pm   #7
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Default Re: HP3325B Mains Input Filter

Just out of interest, Mouser is principally owned by Berkshire Hathaway, the big investment company owned by Warren Buffet, the famous investor. It seems he has a liking for businesses that just get on with doing a good job. I've used Mouser for a number of years and Texas doesn't seem much further away than Leeds or Corby.

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Old 7th Aug 2020, 9:21 am   #8
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Default Re: HP3325B Mains Input Filter

Mark, I assume that Mouser handle the import duty side of things and you aren't likely to get stung by the package being held up and Royal Mail wanting a handling fee? I'll have to look at my HP8640B (earlyish model) to see if it too has a Schaffner filter. BTW I meggered the filter once I had it out and it is nearly short between L and N.

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Old 7th Aug 2020, 12:12 pm   #9
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Default Re: HP3325B Mains Input Filter

Yes, that's all taken care of. Delivery is via courier (FedEx), so it goes nowhere near Royal Mail. Import duties are built into the prices you see on the website. In practice, it's just like ordering from RS or Farnell, and pretty much as quick (2-3 days). And they seem to have a lot of parts (that I'm interested in, at least) that I couldn't find from the big UK suppliers, so that's a win-win
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Old 7th Aug 2020, 2:33 pm   #10
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Default Re: HP3325B Mains Input Filter

Quote:
Originally Posted by Humber888 View Post
Mark, I assume that Mouser handle the import duty side of things and you aren't likely to get stung by the package being held up and Royal Mail wanting a handling fee? I'll have to look at my HP8640B (earlyish model) to see if it too has a Schaffner filter. BTW I meggered the filter once I had it out and it is nearly short between L and N.

Mike
The HP 8640B shouldn't have a Schaffer filter, it will be something more like these (one is made by Corcom).

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There maybe an external RIFA mounted on the back on the filter.
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David
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Old 7th Aug 2020, 2:57 pm   #11
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Default Re: HP3325B Mains Input Filter

I should have checked this thread for your photos David - it would have saved me poring over the service manual to establish the same thing. Oh well. Mark, thanks for that information re Mouser. I'll have to register with them and go from there.

Mike
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