Amstrad 3in disc drive troubleshooting

Jules Richardson jules.richardson99 at
Sun Nov 7 16:19:00 CST 2010

Tony Duell wrote:
>> On 06/11/10 20:03, Tony Duell wrote:
>>> 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...
>> Read as: "I've tested all of these, but I'm selling the broken ones as 
>> 'untested'."
> I suspect, and suspected at the time, that you areperfectly correct :-)
> Before we get another flamewar, I will point out that just about every 
> seller I've dealt with at radio rallies has been extremely honest. If 
> something doesn't work, they say so. If it's missing important parts, 
> they say that too.

I get a bit fanatical about testing anything that I'm parting with - I don't 
like the idea of the recipient finding a problem that I could have found 
myself and told them about. That's always meant I've had a pile of 
"extensively tested" stuff, and a pile of "untested because I haven't had the 

I suppose it's not impossible to encounter that situation at a radio rally, 
car boot sale etc. although I must admit that it's tempting (as a buyer) to 
merge the sold-as-seen and I'm-going-to-get-screwed categories :-)

> Ah, my multimeter lives on the workbench. 

Mine's always bouncing between house, workshop and garage - I'm rapidly coming 
to the conclusion that I need three of everything :-(

>> I'm seeing around 2V on all three pins of the head -- 'top', 'bottom' 
>> and the centre tap. If I switch to AC coupling, 200mV/div, I see what 
>> looks like a very noisy sine wave on the centre tap, and then the coils 
> Trhis is for the selected head? That can't be right!~~~~~~~~~~~~~~~~~~~~

The behavior should presumably be pretty much the same for a 3.5" or 5.25" 
drive (depending on media coercivity - I don't recall what 3" is now); maybe 
it's worthwhile Phil sanity-checking observed readings against a drive that he 
does have around, if he doesn't have a known-good 3" drive handy?



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