• Please review our updated Terms and Rules here

CBM 8050 -- 3 solid red lights

F

fm2606

Member
Joined
Apr 17, 2021
Messages
13
Location
Florida's Space Coast
I recently bought a ton of Commodore stuff. Mainly C64Cs but there was a B128-80 and a CBM 8050. I was going to hold off on working on the B128-80 / 8050 but temptation got the best of me. i plugged in the 8050 and got 3 solid red lights and no drive activity. My next thought was maybe it needed to be plugged into the B128 which I did and powered both on but still 3 solid red lights and no drive activity.

A bit of research and the diagnostic manual says if 3 solid red lights probably UN1 is bad. UN1 = 6502. After a bit more research I see that 6502s are still available. So all I have to do is swap that out is my understanding. Is this correct?

Would a bad 6502 cause the drives not to spin? Or, as I am assuming is the case, this will solve one problem only to unmask what is causing the drives not to spin.

I just feel that there is / will be more to it than a chip swap. Any guidance would be appreciated.

Thanks!
 
Well, since a Commodore drives is basically a computer, with a CPU, ram, rom, etc., a faulty 6502 will surely prevent the drive from working, since the 6502 is the CPU (microprocessor).

Nowadays you can still find 6502 and also some 100% compatible replacement chips on eBay and other stores.
The 6502 should be on socket, so I think it would be a good try to put a fresh 6502 and switch it on. You can find a 6502 inside most of the older C= computer, like PET and VIC-20 (but not C=64). Of course it doesn't mean it will solve, since other ICs could be bad. No way to tell it without a test.

However, before to do that I strongly recommend to check the power line, to be sure you haven't a wrong voltage there. A faulty power line can easily burn more than one IC.

In my experience, a check with a scope is the best option, when possible. In example: I had a PET that refused to boot. Power rails seemed to be good, but the scope showed there was a ripple in one rail. I replaced the big capacitor close to the transformer and it solved.
 
If the 6502 CPU is in a socket, and you can pick one up cheaply, then the easy way is to try and swap it and see what difference it makes.

You are correct in that you may have multiple problems - one being a dead CPU - and fixing one thing will lead to the next.

However, there is no guarantee that it is the CPU that is faulty. A dead ROM could also cause similar results. As could a faulty reset circuit, faulty clock etc.

Do you have any test equipment (e.g. a multimeter, logic probe or oscilloscope)?

Dave
 
Thanks for the replies.

All I have is a multi-meter.

Since 6502s are cheap I think I will just go down that route for now. I really need clean and unload some of these C64s and printers before I get side tracked with fixing the 8050. I plan on keeping the B128 & 8050 so no great rush...as long as I can keep from getting side tracked ... SQUIRREL!
 
fm2606 said:
I recently bought a ton of Commodore stuff. Mainly C64Cs but there was a B128-80 and a CBM 8050. I was going to hold off on working on the B128-80 / 8050 but temptation got the best of me. i plugged in the 8050 and got 3 solid red lights and no drive activity. My next thought was maybe it needed to be plugged into the B128 which I did and powered both on but still 3 solid red lights and no drive activity.

A bit of research and the diagnostic manual says if 3 solid red lights probably UN1 is bad. UN1 = 6502. After a bit more research I see that 6502s are still available. So all I have to do is swap that out is my understanding. Is this correct?

Would a bad 6502 cause the drives not to spin? Or, as I am assuming is the case, this will solve one problem only to unmask what is causing the drives not to spin.

I just feel that there is / will be more to it than a chip swap. Any guidance would be appreciated.

Thanks!
Click to expand...

Troubleshooting guides are not really the best way to repair these old things.
The old CBM dual IEEE drives have a quite complex logic board with two CPUs sharing a common data bus on the two opposite clock phases.
A drive not booting (3 solid leds) can be almost anything that prevents the main CPU (6502) from executing code.
It can be a bad supply rail, lack of clock, lack of reset, any kind of address decoding issue, any kind of rom corruption, any kind of RAM issue and I might go on.
In my own experience, bad 6502 is a rare fault. I only have found two bad 6502 in several years of repairs.
In facts, I started repairing these old things when they weren't that old yet (1986).
You need some test equipment if you really intend to repair the disk drive (and not only swapping ICs hoping for the best), the absolute minimum is a multimeter and a logic probe.

HTH
Frank IZ8DWF
 
I agree with Frank. All you know so far with the three red lights is that there is an issue with the IEEE488 control section of the digital board. Because the two 6502 CPUs in the 8050 share the same data bus on alternate phases of the 1 MHz clock, make sure you use the fastest memory parts available when replacements are needed.

If you need to replace the ROMs, you may be able to use the Motorola 68764 type of EPROMs. They are pin compatible, however you may have to invert the chip select to make it active high.

Don't worry if you can't fix your drive. There are good disk emulators out there that utilize popular SD memory chips. They will look like one huge single floppy drive instead of two small drives.

However this can be an issue if you need dual drives (two units within one IEEE device number) that some applications require like SuperPet software.

Otherwise they are a great solution to your PET storage needs.
-dave_m
 
There are two 6502s in a 8050... you could always swap them and see if it makes a difference... If I remember correctly the first 6502 should start (requires clock, probably some ROM, RAM and at least one RIOT to control the LEDs); the self check does some local checks and then talks to the other 6502, exchanging a request and then continues. To have zero flashes isn't good. A cheap scope or logic analyser will help you... things to check... reset, clock, address and data bus... the usual suspects. I believe the CPUs share a data path... I imagine there are some weird and wonderful failure modes! Good Luck!
 
Sounds like I will be using the SD emulator. I may give this a go but EE is not my forte. I highly doubt I'll be using any software that requires the dual drive and if it does require it, well, guess I won't be using it.
 
Well, I took the day off from work because I could and just wanted to tinker around on some stuff.

I first looked at my TRS80 M3 that I can't get working and, well, it still isn't working. Since I wanted to keep the low self-esteem going for not being able to figure electrical issues out, I got the 8050 down from its perch to have another look.

I plugged her in and checked voltages. They were all -1V from nominal but within the +/- 1.5 V according to the service manual. As I was deciding on what to do next I started to hear a sizzling noise and then a loud bang. Some white smoke came out from between the transformer and back wall of the 8050. Taking it apart I found that the back end of the power receptacle gave way.

Here's a pic: https://imgur.com/a/oTCojUx

Gonna order a new receptacle and try again.
 
Yep, one (or more) of the internal filter capacitors gave up the ghost (literally)! These are some of the typical weak points in any vintage computer I am afraid.

Start a separate thread for your TRS80 and I may be able to help you on that one - but don’t get too many projects on the go at any one time - otherwise you end up like the rest of us!

Dave
 
daver2 said:
Start a separate thread for your TRS80 and I may be able to help you on that one
Dave
Click to expand...

Already started one! The subject is Green Raster Circle, now nothing.

daver2 said:
but don’t get too many projects on the go at any one time - otherwise you end up like the rest of us!
Dave
Click to expand...

Did you say ... SQUIRREL!!!

Definitely not going any further down the 8050 rabbit hole. I bought the 8050 along with a CBM B128-80 and I just got a video cable in so I could test it and it's not working! Going to be starting another thread about that.

Thanks for the help and suggestions.. Maybe I'll revisit this in the distant future but probably will just end up selling it. If I can't get the B128-80 working it is definitely no use to me . If I do get the B128 working I will probably just use a disk emulator.

Thanks again everyone!
 
You must log in or register to reply here.
Back
Top