23 Jul
2002
23 Jul
'02
5:20 p.m.
On Tue, 23 Jul 2002, Tony Duell wrote:
You're right. I wasn't thinking about those.
The 8 pin chips are marked 4558. They probably are op-amps, but I haven't
looked them up yet. There are indeed 4 SMT transistors on A103. I
overlooked them the last time I had the board off the drive.
I certainly don't hear the heads moving, but I'm not sure how noisy these
drives are anyway.
-Toth
I guess its
not exactly a hybrid circuit. Some of those small SMT boards
are coated with the same material most ceramic caps are coated with. Most
of the boards are not coated, and the standard SMT parts are somewhat
I thought some/all of the resistors were formed as thick film components
on the ceramic substrate. Which makes it a sort-of hybrid circuit. accessible. I
think A103 contains 3 small 8 pin chips which control the 4
amplifier transistors. How many transistors made up the original
transistor array?
The original transistor array was 2 NPN transistor and 2 PNP
transistors. A 14 pin DIL package, I think
Those 8 pin chips sound like single/dual op-amps (of which there are
many in the servo circuit). Are there also discrete SMD transistors on
this board? Desolder them, and at least use a diode check (on your
DMM?) to check
the base-emitter and base-collector junctions. And make sure that
collector-emitter tests as open-circuit both ways round.
If you have a better transistor tester (I use a Tekky 575, but then I
would!), you can use that, but then you don't need me to tell you how.
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.
would spin
down if it had trouble reading only some of the servo tracks?
Possibly? But then again, I'd expect it to attempt to move the heads
under such conditions. A drive where the heads don't move is either
locked on-track, or has a servo amplifier failure, at least most of the
time.