Another Crazy Idea: disc drive controller swapping

Philip Pemberton classiccmp at philpem.me.uk
Thu Nov 25 16:47:37 CST 2010


On 25/11/10 22:13, Tony Duell wrote:
>>
>> Here's another idea that'll get me a place in the Loony Bin.
>
> I suspect you're already there :-). I cerainly should be...

Probably... :)

>> Let's assume for a minute that the heads in the EME232 drives are
>> undamaged. That means all the issues are related to defective circuitry
>> on the PCB. So, how about this for an idea: move the controller chip and
>> surrounding circuitry (or even the whole board) to the EME232, then wire
>> it into the existing drive mechanics.
>
> Where are you getting this ASIC (or board) from? If it's another simialr
> drive, then no problem

I was thinking a 3.5in drive (with the DENSITY switch hardwired to 720k) 
or a 5.25in 1.2MB drive similarly jumpered.

Reverse engineer the circuitry (i.e. disassemble and trace out on 
paper), then etch a new PCB to fit the Amstrad drive shell.

 > (although IIRC you have to do the track0 alingment
 > if you remove the PCB).

Nope. Track0 sensor is on a separate PCB, in the mechanical bay. You can 
swap the PCB with no ill effects on the head alignment.

 > Also, IIRC, the ASIC is the same between the
 > signle hardand double head models.

It is. I'll bet it was used on other disc drives as well, though finding 
them would be a fun trick. It's a Panasonic chip, so it's probably fair 
to assume at least one Panasonic drive used it.

> Where are you going to get all the spares from.

Drive mech -- the broken EME232s.
Head amp ASIC etc. -- PC floppy drives bought on ebay. No shortage of 
those, and the circuitry on the Panasonic JU247A seems fairly easy to 
reverse engineer (single-sided PCB, one ASIC and a stepper controller).

> At one time CPC coudl get most Amstrad spares... But I don;t know if disk
> drive parts were amongst them, certainly the service manuals don't seem
> to support field repari of thedrives and there re no parts lists...

I don't think they were -- the manuals explicitly state that the disc 
drives were non-engineer-serviceable. I'd love to get an alignment disc 
for these things...

> One other though, which I mentionedsoem weeks ago. The periperhal
> componens to the read amplifier seem to be those that I would expect for
> an MC3740 IC. I wonder if yo could use that IC and a little external
> circuitry to replace the defective read amplifier secion (and the rest of
> the ASCI seems fine).

I take it you hammed the part number, and that you actually meant the 
MC3470?

That would probably do it -- the catch, of course, is that the MC3470 
seems to be obsolete, and as rare as hen's teeth. Again, unless someone 
in the community has squirreled away a rail of them.

If I had a couple of those, the readback problem is solved, and 
attention can then be turned to writing and the Shugart interface 
(neither of which are especially hard problems to solve with LSTTL).

-- 
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/



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