Amstrad 3in disc drive troubleshooting

Tony Duell ard at p850ug1.demon.co.uk
Sat Nov 6 15:03:54 CDT 2010


> 
> On 05/11/10 22:53, Tony Duell wrote:
> > 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?

As it happens, yes. The scheamtics of at least the single-head drive 
appear in other Amstrad service manuals too. 

> 
> > 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.

Although somebody else has confirmed it/s normal behaviour on the PCW. 

> 
> > 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."

Aha...This remionds me ao a character I saw at a couple of radio rallies 
many yearsa ago. He had a pile of working hard drives. And another pile 
of ''untensted' hard drives. Hmmm...

I wonder if theprevious owner plugged them into a PC power supply and 
then discovered that either they didn't work, or somebody told him he'd 
probably done some daamge, so you ended up with them

> 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.

The scehamtic of the double-head drive gives the pin votlages for the 
ASIC. It owuld appear those are the votlages you'd get if the drive is 
powered, but not conencted to a controller (all inputs pulled high). May 
be worth checking the ones around the read section.

> 
> > 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.

It does sound like head or ASIC problems...


> >>     - Heads. Dirty, out of alignment or otherwise completely pooched.
> >
> > Well, clean the heads!.
> 
> 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.

OK. You';ve orblaby elimniated that as a cause. 

> 
>  > 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!)

You put the DMM away? That suprises me ;-)

> Good point.

> > Do you have the schemciats?
> 
> I have the PCW8256/8512 service manual, the 8256-only service manual and 
> the 9512 service manual as PDFs, which include the drive schematics.

Right I haev some of those as paper manuals.

I think I would start by checking the pin voltages on the ASIC, and in 
particular see what the head cnetre-taps are doing.

-tony



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