HP ScanJet ADF

From: Tom Uban <uban_at_ubanproductions.com>
Date: Fri May 31 14:22:02 2002

Close call. The problem turned out to be a shorted SMD bypass capacitor,
not a tantalum. I've seen thru-hole tantalums fail in the past, but I
haven't had much experience with SMD repair (until now). I checked the
capacitor after removal to be sure that it wasn't just a solder problem,
but it was in fact shorted! Fortunately, I was able to salvage the two
other SMD parts, one SO-8 and one P-DSO-24-3, which I had also removed
in order to verify that they were not the cause of the short. I had
considered just cutting the legs to remove them, but used a pointed
scriber to lift the legs instead. After cleaning the solder off of both
the board and the legs, and then straightening the legs back to the
proper pitch and height, I was able to replace them onto the PCB ok.
After putting the PCB back into the ADF and hooking it all together,
the scanner now operates properly with the ADF -- woohoo!!!

I guess that I just saved some more space in a landfill somewhere for
someone elses ADF unit, because HP won't sell parts for these units.
Imagine what HP will do with anything that Compaq managed to save from
DEC (though I don't imagine that would be much)...

Thanks for everyone's advice!

--tom



At 06:32 PM 5/31/02 +0100, you wrote:
>
>Tom Uban wrote:
>> I guess I will just proceed with repairing the board. The 24v input seems
>> to be shorted to ground -- that shouldn't be to difficult to find.
>
>Just a suggestion: I fixed an HP 1980B oscilloscope that had a shorted
>power supply by replacing a shorted tantalum capacitor. Tantalums
>tend to go short-circuit for no good reason, and result in the
>short-to-ground symptom that you mention.
>
>--
>John Honniball
>coredump_at_gifford.co.uk
>
>
Received on Fri May 31 2002 - 14:22:02 BST