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Commodore 8050 Disk drive problems.

M

Max1227

Experienced Member
Joined
Jul 4, 2015
Messages
78
Location
UK
Hello everyone.

I recently got a 8050 disk drive that doesn't work and I was wondering if there was anyone in the UK that might be able to service it to revive it to a working state?

I did have another thread open discussing the problems with my commodore PET model 8096 so I'm sorry if I irritate anyone by having two threads open as I have done on other forums, sorry but I just don't have the technical know-how to close it.

Any help would be greatly appreciated as I really would like to get this working. Just to give a brief description of what it does do far - The lights light up however the middle one stays red and the drive 0 light remains green, occasionally drive 1's light flashes. If I switch the drive off and then on immediately the centre LED sometimes goes green. One user suggested to me that it was bad caps which I can certainly believe. I know of one user who does repairs and lives relatively close to me however I cannot remember his/her username and if they are on this forum.

Thanks in advance and I can load up pictures if required for a proper diagnostics.
 
Max1227 said:
Just to give a brief description of what it does do far - The lights light up however the middle one stays red and the drive 0 light remains green, occasionally drive 1's light flashes.
Click to expand...

See pages from the 8050 Service Manual here: http://zimmers.net/anonftp/pub/cbm/schematics/drives/old/8050/index.html
Here is the Flash Code from P. 5:

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Hello,

Unfortunately there is no repetitive flashing so the blink codes are not very helpful for disposing this problem. Another reason I say this is the because when I first got the drive it gave me different results every time I turned it on, for example, if I turned it off and on repetitively and centre light would go green, if I turned it off then on after 10 seconds the centre led would turn orange, most of the time it stays red and there is no flashing on power up.

I think it is either a bad capacitor or a fault with the main 6502 chip at UN1.

Thanks,
 
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Max1227 said:
I think it is either a bad capacitor or a fault with the main 6502 chip at UN1.
Click to expand...

If the +5 and +12 voltages are OK, then don't worry about capacitors at the moment.

The UN1 6502 controls the IEEE488 bus, while the one at UH3 controls the data transfer of the drives. Hard to say right now if either one is bad.
 
Hello,

So if the voltages are okay - where do you suggest I go next?

Thanks,
 
Max1227 said:
Hello,

So if the voltages are okay - where do you suggest I go next?
Click to expand...

Hook the unit to a working PET and try to get disk status with: print ds$

If nothing comes back, then perhaps the IEEE part of the drive is kaput. You can also check the CPU SYNC signal (pin 7) to see it it is pulsing. That will say the CPU is fetching instructions. These disk drives are quite complicated. They have dual CPUs running on opposite phases of the clock and sharing a RAM data buffer. You will soon need an oscilloscope or logic analyzer to troubleshoot this box and god help us if the problem is in the analog controller. But let's not worry about these things until we run out of the easy things to check.
 
Also important is the fact that SYNC is pulsing because that also means the processor isn't always fetching instructions. It's fetching instructions and data, which it won't do both if certain things are just wrong.

I don't know too much about these drives yet, though I'm getting a crash course just now. I have a 9060D that is acting up. I found both CPUs are running, so I punted, and I'm replacing the 2114s before I go any further. I'm currently waiting for them to show up. I only had two in my inventory, and I used a /very/ quick but destructive desoldering method I just discovered. If I knew I only had two I wouldn't have done that.

Max, I wouldn't recommend rapidly cycling the power, that can cause damage. It also is the only rational way I can think of for that LED to turn orange. If it happens otherwise, I might expect a bad RIOT.

I agree with Dave fully. The important first step is getting a working GPIB device to properly get the status and see what it is. The simplest way is ?DS$ on a working BASIC 4 PET.

In case you can only try with a BASIC 2 machine, use
Code: 
0 OPEN1,8,15:INPUT#1,A$,B$,C$,D$:CLOSE15
1 PRINTA$,B$,C$,D$:END
RUN

Matt
 
Thanks for the help, looks like I need to get myself a IEEE-488 cable in that case.

To be perfectly honest I don't think much in that drive is working. Every time I load a floppy into the mechanism the motor spins and turns the floppy for a few seconds and then stops, however the drive will not lock down in position, so even if I do fix the electronics it still won't be able to read a disk unless Iam constantly pushing the drive mechanism down. Is it meant to be like this or is it broken? At first I thought the motor was locking it down.

Thanks,
 
Hey Mac

I have one of these units and if it's the drives I have, they latch when you push down. Mine are a little tetchy about it, but I haven't serviced them yet (bought from some local guy, they're in need of a good clean). So check the latching mechanism first.

Cheers
JonB
 
Hi Jon

Okay, that's another problem that needs fixing as mine don't latch down anymore. They simply click then spring back up, but the odd thing is that the latching mechanism has broken on both of the drives.

Thanks,
 
Max1227 said:
Okay, that's another problem that needs fixing as mine don't latch down anymore. They simply click then spring back up, but the odd thing is that the latching mechanism has broken on both of the drives.
Click to expand...

It's a common failure item. On my 4040 drive, I only needed to adjust one latch, and on another, it was broken. Long long ago, I traded with Anders (forum name: carlsson) for a latch. He may check in here if he has any components left. You should identify the make of floppy drive or provide a good photo of the latch. I think there are several types.
 
Hello

I attach a picture of the model of disk drive that I have.
If you would like a serial number or model number I can get that for you soon.
image.jpg
 
Okay I'll take a look. It is much easier for me to look at the disk drive compared with the pet.

But seeming both drive latches are broken I don't think I'll be able to refernece it.

Does anyone have a picture of what the latching mechanism should look like? I did take a look ages back when I got the drive but I couldn't immediately see anything that was broken or damaged.

Thanks.
 
I'll have to inspect mine. Unless I'm mixing up drives, there is a plastic dowel that runs parallel to the front of the drive, and is inserted inside the latch. It is common that it quits fitting in a press-fit part on each side. I fixed mine with cyanoacrylate.
 
Hello,

Okay, so I checked both chips at UN1 and UH3 and replaced both of them and the disk drive still doesn't work? I also checked the chips at UN1 inside a pet and it worked perfectly.

Any ideas where to look next.

Shout out to Dave at Tynemouth software for helping me with everything listed about and to all the people on the forum that helped with the voltage testing and identification of the boards.

Voltage in both the pet and disk drive are good.

Thanks,
 
Well I blindly replaced all the 2114s in my D9060 and it sprang to life, at least until the power supply gave out.

I've had to replace 2114s in everything I own that uses them. Based on that, I'd recommend replacing those at this point.
 
Hello,

Okay so I've managed to get the disk drive working!
I replaced the 6532 chips using ones from the broken tractor printer and the drive past the self diagnostics test!

Now all I need to do is find a IEEE-488 cable and fix the latches.
Any tips on fixing the latches?

Thanks,
 
Like Dave said, you'll need to determine which drives you have first. If memory serves, there were three different ones. I think mine are Micropolis.
 
Hello,

Okay so is there a method of identifying the drive? Or it it just simply in the serial number?

Thanks

Just a quick update: I can manually make the drives latch down by twisting a piece of plastic however this will not happen automatically using the spring system. Sorry for the bad description but I can't upload a photo right now.
 
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