5 Nov
2010
5 Nov
'10
6:03 p.m.
On 05/11/10 22:53, Tony Duell wrote:
I haven't checked the centre tap. I've just found a test/adjustment
procedure in the Amstrad manual which suggests that the ASIC tries to
float the head in relation to ground, but that the absolute voltage over
the head is zero unless it's in use. That might explain the strange
measurements.
That's good to hear...
Done that (with a cotton bud and Servisol IPA-170 Isopropyl Alcohol). No
change in behaviour, no dirt on the cotton bud I used to clean them.
I have the PCW8256/8512 service manual, the 8256-only service manual and
the 9512 service manual as PDFs, which include the drive schematics.
Thanks,
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
I have scheamtics that might be related. The main ASIC
seems to be an
M51017Ap in both cases.
Yep. I think I might have the same schematics. Amstrad PCW 8256/8512
Service Manual?
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?
Not yet, no.
If getting the power lines backwads does do damage, is
it psosigle that
the otehr drive was damaged before you got it?
I'd go with "probable". They were sold to me as "spares or repair, no
idea if they even work."
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. Anything on TP1,2 on the drive PCB? Those are the
differential outputs of
the read amplifier, used for head alignment.
Nope, nothing on either.
- 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).
On the to-do list (it's a bit late to be getting out the DMM at this
time of day!)
Out of alignment won't make a
difference, you are reading and writing with the same head, in the same
position.
Good point.
Can anyone
suggest some things I could check, or are these drives likely
to be toast?
Do you have the schemciats?