5 Nov
2010
5 Nov
'10
3:53 p.m.
OK, this is seriously weird.
I have two Amstrad 3-inch disc drives: an EME-156, and an EME-231.
I have scheamtics that might be related. The main ASIC seems to be an
M51017Ap in both cases.
Both drives will spin up, select and generally "work". For varying
values of "work". On both, the "activity" (selected, whatever) LED is
stuck on at half-brightness, but switches to full brightness when the
drive is selected.
I an't see why it would do that. According to the schematic, the LED is
driven by pin 44 of the ASIC, have you stuck a 'scope o nther to see if
the half-brightness is actually a square wave?
For reference: both drives are showing the exact same symptoms.
If getting the power lines backwads does do damage, is it psosigle that
the otehr drive was damaged before you got it?
I can select the drive, spin the motor, and seek around the disc.
Writing seems to work (more or less) -- when WR GATE goes low, the coils
of the head are driven to ~10V with smaller positive and negative pulses
(sort of like an exponential curve, synchronised with the falling edge
of WRDATA). When WR GATE goes high again, the head voltage falls back to
about 2V.
I am not convinced that's right. What is the centre-tap of the head doing
(ASIC pin 18 for side 0 and pin 20 for side 1)?The head should be a
low-resistnce device and if you're getting 11V across it, something is wrong.
When I try and read anything, the head shows no response whatsoever. No
pulses on either side of the head at any amplitude (measured with a 1:10
probe on a Tek TDS2024B). Similarly, RD DATA shows no pulses either,
except for a brief glitch (2.8us or so) when the drive is selected.
Anything on TP1,2 on the drive PCB? Those are the differential outputs of
the read amplifier, used for head alignment.
FWIW, the peripheral components around that bit of the ASIC look very
like the ones used on a MC3470.
- Discs. The discs aren't actually magnetically
coated in any way, or
the coating has failed in some way. Catch is, I don't have a known-good
disc to test with.
I think that's unlikely
- Heads. Dirty, out of alignment or otherwise
completely pooched.
Well, clean the heads!. Check the DC resistance (should be very low
between the 4 wires going to a head). Out of alignment won't make a
difference, you are reading and writing with the same head, in the same
position.
Can anyone suggest some things I could check, or are
these drives likely
to be toast?
Do you have the schemciats?
-tony