24 Jul
2002
24 Jul
'02
2:10 p.m.
On Wed, 24 Jul 2002, Tony Duell wrote:
Thats good news I guess.
If the 4558 is common, why would I not find them?
Of course, I'll have to reassemble the unit again. I'm afraid I'm gonna
wear the connectors out taking the boards off so much. Maybe I should
build some cable extenders to help while troubleshooting...
-Toth
The 8 pin
chips are marked 4558. They probably are op-amps, but I haven't
The 4558 is a very common dual op-amp. I don't
have a really nice transistor checker yet, but I do have a couple
of pocket types that work well. I desoldered and tested all 4 1N4001s and
all 4 transistors. I checked all of them with a one of the small testers,
and then checked them all again manually with my DMM. None of those 8
parts appear to be bad.
Pity. So the fault is elsewhere. Alas the rest of the circuitry is
sufficiently different in layout that I probably can't help you. I could
tell you that there are interesting signals on the outputs of op-amps,
but you'd never find them on your board. But if you can get a 'scope, try looking at the
signals on the 2 pin
servo input connector (preferably use a 'scope with differential -- A-B
-- mode). It would at least tell you if the servo head is reading
anything.
I actually have a lead on some P6120 probes for my Tek 2213 scopes now, so
maybe I'll be able to use them in a few weeks. Now if only I could find
the Operator and Service manuals...
I certainly
don't hear the heads moving, but I'm not sure how noisy these
drives are anyway.
Try holding the drive in your hand as it spins up (you only need to have
the power cable connected, of course). You can normally feel the heads
moving.