Reviving a dead 1541

[srowe]

Well, I've got it out and tried it in a test circuit. It seems to be ok but I've ordered a replacement to make sure. On to UD2 I suppose.

[pitcalco]

I would guess the ROM is bad if you've tried the other bits, but it could also be the VIA.

I''ve just opened a spares section of my shop (see my post in this forum) for exactly this kind of thing. I should be getting in some 6522 VIAs soon, and I can already do a replacement ROM.

Where in the world are you? If you're in the UK you can send me your VIAs and ROM and I'll test them all for free. If one of them comes out faulty I can then supply the replacement, so you don't have to keep buying replacements until you find the culprit.

Just let me know if I can help!

Wow! I was hoping to find someone like you!

I would be interested in getting some help from you as well. I have a 1541 with the same trouble. I looked carefully through the troubleshooting manual I found on Bombjack and I am pretty sure that that the disk ROM is bad (i.e., the start up routine does not run properly). I was hoping to find someone with the means to fix this.

Of course, I would cover the shipping as well as any expenses you may have to fix my drive, and reimburse you for your time. Is this something we could arrange?

P.S. I also have a 1571 that needs fixing. Can you help me with this too?

[Spirantho]

Hi,

I run this as part of my business (it's more of a hobby-business, though, if you see what I mean - the real money comes from the boring embedded work. ) but I can probably fix your drives for you, yes. It's not guaranteed because some of the chips on there are a nightmare to find, but I can give it a good go.
I'll sort out your 1541 and your 1571 for you for £50 + postage if you like, but I'd STRONGLY recommend just sending me the logic boards - the rest of the drive is way too heavy.

Let me know by PM or email (note the spamfilter text! ) if I can help so we don't derail this thread any further.

[srowe]

I think the 7417 is gone. The outputs are giving low voltages that don't follow the inputs.

[srowe]

Well, I've replaced both UA1 and UD2 and the symptoms are the same.

In summary

I've checked the output voltages of both rectifiers
The 5v rail reads 4.93v
I've tested the 6502 and both VIAs in my VIC
I've dumped the contents of both ROMs and the md5sums match images I've downloaded
I've replaced UA1 (74LS14) and UD2 (7417) with new parts
Verified that /RESET goes from low to high at power on

Any suggestions about what to try next?

[Spirantho]

Is the disk definitely turning? Otherwise I think you'll just have to test all the other ICs....

[srowe]

Yes. Symptoms are

On first power up red and green LEDs come on. Drive motor also on. After a while red LED goes out but drive motor still spins.
Subsequent power cycles, LEDs and motor come on, all stay on.

[Spirantho]

You say that the drive motor stays on but does the actual drive spindle turn? I just want to be sure that the belt isn't slipping.

Otherwise it really does sound like a fault I had with the 74LS14. Given that you've ruled that out, though, I'd say it's another of the logic chips. Are you able to test the other 74LS chips? There's not that many of them luckily.

[srowe]

The drive spindle is definitely turning and the belt tension seems fine.

I've found a list of chips to check on one of Ray's comp.sys.cbm postings

UA1 - 74LS14
UB4 - ROM
UC2 - VIA
UC4 - 6502
UC6 - 74LS04
UC7 - 74LS00
UD3 - 75LS86
UD5 - 74177

I've checked/replaced the first four, I'll work my way through the rest (although I'm running low on sockets)

[srowe]

Success! I've just replaced UC7 (74LS00) and the drive now powers up and I can read the directory off a disk.

There's something to be said for hardware that so straightforward to repair. They don't make them like that any more.