Re: 8050 which will write but not format

From: Rob Clarke <>
Date: Sat, 01 Dec 2012 16:50:42 +0100
Message-ID: <>
Here you go Julian, this is the 8296D diagnostic disk :

Well, I cranked the speed down to around -6ms to slow (I assume that's 
milliseconds per revolution) and it appears to format more - it got to 
around track 20 before barfing.

You're right in that when I had it set to 0ms I can write to the whole 
disk. I filled all 2260 blocks on the suspect drive and verified the 
contents on the other one. Go figure... :-/


On 01/12/2012 15:34, Julian Perry wrote:
> Hello Rob,
> Saturday, December 1, 2012, 11:47:58 AM, you wrote:
>> Hmm, thanks Julian - I have checked and adjusted the speed with the
>> 8296D diagnostic tool and it claims they are bang on. It also measures
>> the variation, which it also claims is OK. Should I have reason not to
>> trust it?
> I'm not familiar with the diagnostics tool (wouldn't mind a copy,
> actually - I have an 8296LP).
> With a 1541 format,  the whole track is overwritten with Sync ($FF)
> bytes (about a track and a half), then a chunk of NON sync bytes ($55,
> or 01010101) is written out, guestimated to be about 1/2 the track.
> Sync and Non-sync bytes are counted, and the ratio used to calculate
> the number of "tail" bytes" after the data sector. I can't see that
> there would be much difference between that, and the higher density
> 8050 format.
> Once again, with the 1540/1541, whilst data is read from a shift
> register after the data is clocked in, Sync is detected by a separate
> circuit (integrated into a single chip in the case of the 1541).
> The thing I can't understand is that 5 sync marks are written out
> whenever you write out a data block - and you say that works OK.
> If there was a problem reading sync marks written by that analogue
> board when (re)writing sectors, then you would get error 22 (Data block not found) messages on
> sectors rewritten using that drive - but you don't..
> More thinking (and rom study) is needed :)
> Julian
>> rob
>> On 01/12/2012 01:41, Julian Perry wrote:
>>> Rob
>>> You will get that problem if the drive spindle is running to fast.
>>> Julian
>>> Saturday, December 1, 2012, 11:17:18 AM, you wrote:
>>>> Gents,
>>>> I would not normally post 'please help me fix' type questions here but
>>>> this one has me stumped. Some may already have seen the thread on
>>>> vintage-computer forums here:
>>>> In a nutshell, drive 1 works 100%, drive 0 will read and write but not
>>>> format. It usually stops on track 1 with a #21 read error but
>>>> occasionally will go as far as track 3 or 4. If I swap the mechanisms,
>>>> the problem stays with drive1. This implies a problem in the analogue
>>>> board (micropolis pcb #8050006) but I can't find it and I don't
>>>> understand what kind of problem would allow it to write but not format.
>>>> I know the mechanisms are good and well aligned and, as the drives read
>>>> OK, they are properly speed adjusted.
>>>> Do any of you disk wizards know the algorithms by which these drives
>>>> format a disk? I hoped this might give me a clue.
>>>> Rob
>>>>          Message was sent through the cbm-hackers mailing list
>>         Message was sent through the cbm-hackers mailing list

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Received on 2012-12-01 16:00:10

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