Reforming caps and CRTs
ard at p850ug1.demon.co.uk
Wed Apr 22 15:12:58 CDT 2009
> Tony Duell wrote:
> > > I was repairing an HP 9815 (desktop programmable calc) a month ago. While
> > > tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
> > I am wondering why you traced out the schematic of a 9815, when you can
> You are free to wonder.
> > download both the official service manual (boardswapper guide) and
> > unofficial full schematics (covering both main versions of the CPU board)
> > from http://www.hpmuseum.net/
> The service manual I found previously, and contains the schematic only for
> the power supply (which I had already RE'd by the time I found the manual).
I don;t know where you found that manual, but it is certainly available
from hpmusuem.net, along with the schematics of the 9815 (and many other
> IIRC, during a web search I saw something about a schematic or full service
> manual available on a CD.
Ah yes,, the HPCC schematics CD. That contains the same schematics as on
hpmuseum.net along with a few others and ones for most of the LED HP
handhelds. FWIW, foe all I spent _many_ hours producing those, I don't
get a penny (cent, whatever) from the sale of the CD-ROM.
> Anyway, it (my RE'd schematic) is all done.
Well, if people would rather produce their own, I'll stop doing them
unless I also need them....
> > Alas I didn't keep the one I replaced in the HP120, so I can't check that.
> I suspect it is as Dwight was suggesting, the cap probably isn't doing much of
> anything and the lack of C just doesn't matter in the scenario.
Almost certainly. It was just a decoupler on the 12V rail (and not a
particularly good one, the HF stuff being taken care of by several
ceramic capacitors).. I didn't other to test it, when I found it was in
backwards, I dug out a replacement and fitted it. On the grounds that
correcting a thing like this prevents 'interesting' problems later.
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