Problem with HP 8904A power...


I have a NOS 8094A - it has about 2 hours on the clock, and today, just after powering it off, there was a plume of smoke from the back and a lot of "hissing". dead capacitor, I say to myself...

had a GOOD look inside. With a magnifying lamp. Nothing, except...

...there is a tarry deposit that smells the same as the smoke did round the back of the main inlet IEC filter and a few spatterings of same on the inside of the top cover above the filter and to the right (looking from the back). I suspect, that for the first time in my career, I've a mains filter failure...

However, a) its rivetted to the back plate (no real problem), and b) I have no spares part number for it, and c) its a sealed unit, and this a module replacement...

Is this a known failure mode for these units? Where could I get a spare filter?

I should point out that it still powers up ok, but I'm understandably not happy with it until the filter is replaced.

Any help appreciated...

Many thanks

Reply to
Mike Deblis
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Hi Mike, the 8904A service manual is available for download from Agilent.

From what I see in my copy is that the connector is part of the loom W1 and the connector is not identified seperately.

I just opened the top cover of mine and it's not a filtered connector. These usually have a a silver box on the back of them with the caps and inductors. From what I see , the filter is contained on the power supply board, a large X2 cap is there as well as inductor etc.

Having said that - is it a 8094a or a 8904a - 600kHz ARB? Your subject says

8904a and your post says 8094a?

The 8904A has two caps on the power supply pcb just behind the IEC connector, perhaps one of those?. These are after the bridge rectifier.

if it is the arb - does yours have any options apart from 1 & 3? If so could you list the code numbers on the label inside at the back for those options.

Thanks Greg

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Hi - thanks for the reply...

I removed the failed filter and can now see the p/n - its a Schaffner FN326B-3/01 - the back has blown with all sort of oily gunk.

A new one from RS in the UK (Scaffner p/n FN 326-3/06) is about $7, so I'll just slip one of those in.

The unit is an 8904A Synth. Options 2 & 4... Everything seems to run ok. Only problem removing the old one was that HP had pop-rivetted the connector to the back plate which had actually fractured the mount. Pretty poor, really. Just used a reamer to remove the rivets, and all is fine - new one will be fitted properly!


Reply to
Mike Deblis

HI, interesting, my 8904 doesn't have a filtered IEC and is also riveted. The power supply board clearly does have a filter, perhaps it's a change made sometime during manufacture, my SN is 2923 is yours earlier or later? Perhaps a change, if your's is earlier, due the problem you mention re the cracking of the connector?

The manual on the Agilent website is for SNs 27612 thru 2948

Cheers Greg

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