13 Dec
2015
13 Dec
'15
7:48 a.m.
On 12/12/2015 08:27 PM, Mike van Bokhoven wrote:
Can do, I just wasn't sure if the ROMs are tied to a particular board
revision (so I need rev A ROMs for a rev A board etc.). Looking at my Rev A
and Rev C boards though it would seem that they have the same part numbers,
and I assume they'd be different if the contents were.
:-) Gotta love 'em, just for how quirky they are - I really don't know
what Commodore were thinking when they designed them (even if they'd worked
as intended with a higher transfer rate).
I do have a drive unit for a Research Machines system designed along
similar lines (on-board CPU and serial connection to host), but at least
that is a dual-drive unit and uses an off-the-shelf FDC.
cheers
Jules
Locked on LEDs and spindle motor would suggest VIA to
me, though it's been
many years since I've looked at one. First thing I'd check is that there's
activity on the address/data buses.
I don't have a lot of test gear, but I suppose poking at A0 with my DMM on
frequency setting should give a sign of whether anything's going on...
If things are going on, and there are 6522s at hand,
I'd try a quick swap.
I can certainly borrow ones from one of the good drives - I suppose given
that the PSU rails are OK, it's unlikely that there's anything in the
faulty drives that will damage them.
I read
somewhere that ROM faults aren't unheard of, ditto with 6522 VIA
failures. Also the 74ls14 at UA1 (particularly if someone's unplugged the
drive from the host with power on), but I think that affects CPU reset,
which appears to be working in my units.
Can you swap ROMs in from one of the booting drives? Worth a go, though
I've never seen a ROM failure. Also, has
there been a worse external drive in the history of floppy
storage? Slow, complicated, expensive and unreliable seems to have most
bases covered ;-)
I sort of agree, though I have to say that of my pile of about 30 1541s and
1541 IIs, all but two ran up fine on first test, after having been in
storage for 25 years. One had a bad 6522, and the other had an alignment
issue. They were all still amazingly slow though!