Printer help?

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Thu Sep 9 00:17:59 2004

>> Does the collective list wisdom include repair hints for an HP
>> LaserJet IIISi? [...]
> Alas I've only worked on series 1 (CX) and 2 (SX) printers. But those
> I have _worked_ on (as in totally taken apart, investigated,
> reassembled -- without the manuals).

Well, while my IIISi is a long way from being _totally_ taken apart,
I've done a good deal with it. :)

>> it was making an odd ticking noise. I went to see what was up and
>> smelled that unpleasant smell that usually means the magic smoke has
>> been let out of something.
> Maybe an SMPUS that's tripping due to a short on the secondary side
> somewhere.

I believe your guess is correct.

> The SX is _very_ modular and comes apart into official FRUs in about
> 10 minutes.

Actually, so does the IIISi - once you know how. But it's more like
half an hour to 45 minutes if you have no reference and no experience.

Anyway, I believe I've now found the offending bit.

By the time I got it down to the point where anything more would mean
some pretty major mechanical work - I'd pulled apart all the
obviously-accessible electronics, and anything more is either more
electrical than electronic (eg, motors) or very delicate stuff I am not
about to mess with (eg, the driver circuitry for the laser) - by the
time I reached this point, I'd failed to find anything obviously fried.

So I put it back together but with one side tipped down, in the hope I
could see something. It's possible to reassemble it electronically
without completely reassembling it physically - in particular, it's
possible to have most of the electronics in view.

I then turned it on. Power came on and I saw some very brief visual
event - looked like a flash of light, but as I wasn't foveating on it I
couldn't really be certain - from a place where there is no component
designed to do anything visually detectible. There was a small tick,
and power went off again. A moment later power came back and I saw a
wisp of smoke curling up from about where I saw the flash of light; it
then blinked out again. Thus, I believe you are correct that the power
supply was sensing overload and cutting out, repeatedly.

Power off immediately, of course.

Then I extracted the relevant PCB and inspected that spot closely. It
appears that an electrolytic cap has sprayed some black substance out
from between the cap and the board, coating everything in the vicinity
(which fortunately is not much - just another similar cap and some
incoming wires).

The cap appears otherwise undamaged to an in-situ visual inspection,
but it's fairly obvious to me that it is Not Healthy. Fortunately,
it's mounted through-hole rather than a surface-mount (while I'm
willing to believe the list that surface-mount components are
replaceable, I do not want something like this to be my learning
experience on the subject!).

Also fortunately, it's a common-as-dirt value (220?F 35V), though since
it appears to be a power decoupling cap, the exact value is probably
not critical.

I doubt I will have the leisure to replace it anytime soon, though,
even though it means my printer will be down; the next couple of weeks,
at least, are looking..busy.

/~\ The ASCII der Mouse
\ / Ribbon Campaign
 X Against HTML mouse_at_rodents.montreal.qc.ca
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
Received on Thu Sep 09 2004 - 00:17:59 BST