Re: Two 1541-II drives with problems

Hello.

And thanks for your thoughts, everybody.

I actually have two (very old) oscilloscopes, but both are in storage now so I have no chance of getting them up and running now. Also I have very little idea on using those.

I have heard of the problem where the drive head gets driven out of its normal way, and can't find the directory. I think I had that once but it still gave me some kind of error reply, so I don't think it's not related to what I have at hand now.

I did some work on the drives today, but I am not sure if this can be called progress.

I socketed the U6 6522 on one drive (I'll call it the drive 2, it's the one that has broken top cover and it's missing the locking lever). The one on which I already replaced the small U7 logic chip. De-soldering the chip wasn't as painful as I called it (actually I did that faster than any previous chip removal, didn't broke any traces and I even managed to extract the chip undamaged!).

I think I had mis-diagnosed the drive 2. It had a flaky power switch, and sometimes it didn't start right away (both leds stayed on). I thought this was a matter of the broken power switch, and it usually started fine after couple of tries. But as I now removed the switch and wired it to permanently on, it doesn't start (both leds stay on). Perhaps I just magically got it up before by reseting it by turning it on and off?

The drive 2 still does not work (leds stay on), and it seems to be not related to the U6 6522, as I tested it with a working 6522 from a working-1541. I also tested the extracted 6522 on the 1541 drive and it works (drive powers up, and thrue a ZoomFloppy I got a directory listing without any problems). So at least I have a spare 6522 chip now.

I think I'll now concentrate on the better looking drive 1, and get on socketing it's chips.

(Sorry if the text above was hard to follow :)

--
Ville



silverdr@wfmh.org.pl kirjoitti 20.4.2014 kello 11.58:

> 
> 
> On 19 April 2014 14:14:23 CEST, Ville Laustela <ville.laustela@gmail.com> wrote:
> 
>> - power on: normal activity (power led on, spindle runs and drive led
>> lights for few seconds, then stop)
> 
> That's good. Means that it found no internal problems. The worst usually is when the led remains on all the time
> 
>> - connected to a C64: drive resets with the computer normally
> 
> You mean when you power the computer on? There goes a RESET line along the cable. If the drive passes its POST at power up, you can quite safely bet that it will pass the reset correctly as well. At least I haven't seen a single case that would not. 
> 
>> - attempting to load halts at "SEARCHING FOR": drive spins (with leds
>> on) but the stepper doesn't move. Only way out is to reset the
>> computer.
> 
> Which tells us that the communication from the computer to the drive works more or less fine (drive received expected commands and tries to deliver results). The problem looks like the communication back doesn't work. This would indeed point to the ICs mentioned below. 
> 
>> 
>> By the Ray Carlsen's website
>> (http://personalpages.tds.net/~rcarlsen/cbm/1541/1541-II/1541-II.txt)
>> these symptoms point to either U7 logic chip (7406) or U6 VIA (6522).
>> On one of the two drives I replaced the U7 chip but that had no effect.
>> 
>> Before I start a (lenghty, painful, boring...) removal of the 6522 VIA,
>> I would like to ask here if anyone would have any other ideas?
> 
> If you have a way to check the serial lines with a scope that should shed more light. But.. manage your expectations and be prepared for the boring job anyway. While one can never be 100% sure, odds are good that new VIA is your friend there. 
> 
> -- 
> Sent from mobile phone (so please have understanding).
> 
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