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Thread: Seeking guidance on Commodore 8050 troubleshooting

  1. #1

    Default Seeking guidance on Commodore 8050 troubleshooting

    My Commodore 8050 is being used in combination with a Pet 8032 (running Basic 4.0)

    Good news:
    • Power up diagnostics does not show any errors, I get a solid green LED. That wasn't always the case but I replaced the two 6532s and that fixed the 'zero page' issue that I was initially getting.
    • Both drives spin and heads move. Initially the heads wouldn't move so I replaced the 6522 and that fixed the problem. I also replaced the two 6502s for good measure.
    • Heads have been cleaned
    • Continuity checks have been performed on the IEEE cable and no issues were detected


    Current issues:
    • Header commands fails: head appears to remain on track 0 and doesn't move, drive stops spinning after a while and the computer displays a 'bad disk' error. A print ds$ command returns a 'read error'.
    • Directory and Catalog commands have no effect, the computer returns immediately to the ready prompt and the 8050 doesn't react to them.
    • The same issues were replicated on another Pet (8296) with the same 8050
    • I don't have a 'known to be working' 8050 disk that I can use to test the read circuitry (ideally with 8050 diagnostics program(s) on it), nor a 'known to be working' blank disk to test the write circuitry. If someone could mail me such disks, it would be greatly appreciated. I am located in Florida.

      Any guidance/assistance would be greatly appreciated! I don't know where to go from here.

  2. #2

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    Quote Originally Posted by retrobecanes View Post
    My Commodore 8050 is being used in combination with a Pet 8032 (running Basic 4.0)

    Good news:
    • Power up diagnostics does not show any errors, I get a solid green LED. That wasn't always the case but I replaced the two 6532s and that fixed the 'zero page' issue that I was initially getting.
    • Both drives spin and heads move. Initially the heads wouldn't move so I replaced the 6522 and that fixed the problem. I also replaced the two 6502s for good measure.
    • Heads have been cleaned
    • Continuity checks have been performed on the IEEE cable and no issues were detected


    Current issues:
    • Header commands fails: head appears to remain on track 0 and doesn't move, drive stops spinning after a while and the computer displays a 'bad disk' error. A print ds$ command returns a 'read error'.
    • Directory and Catalog commands have no effect, the computer returns immediately to the ready prompt and the 8050 doesn't react to them.
    • The same issues were replicated on another Pet (8296) with the same 8050
    • I don't have a 'known to be working' 8050 disk that I can use to test the read circuitry (ideally with 8050 diagnostics program(s) on it), nor a 'known to be working' blank disk to test the write circuitry. If someone could mail me such disks, it would be greatly appreciated. I am located in Florida.

      Any guidance/assistance would be greatly appreciated! I don't know where to go from here.
    6502 almost never fail, I have only one failed in my (large) collection of failed MOS chips, but I digress.
    A read error on what track, sector?
    First, you don't say if you have the schematic, if you don't, I suggest to get it here:
    ftp://www.zimmers.net/pub/cbm/schema...050/index.html
    Did you check the head's coil resistance? Heads have two coils, one center-tapped is the R/W head itself, you should read between 15 to 30 ohms between the center tap and both ends. Then there's an erase head, single ended with one end in common with the center tap of the RW coils. It should measure between 15 to 30 ohms too.
    You can do these checks (obviously with all powered off) directly on the head's connectors. On the only 8050 that I've seen, the analog board is mounted over drive 0 and the head's connectors are on the front-left side of the analog board. I can't tell what are the colors of the conductors (center - RW1 -RW2 - ERASE) but you should find it out with a few checks (or from the schematic).
    If the head coils are good, there's a good chance that the disks you're trying to format are bad.
    Are they SD/DD disks? HD disks won't be formatted by these drives.
    Do you have an oscilloscope, or logic probe or other test equipment?
    HTH
    Frank IZ8DWF

  3. #3

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    Here is the read error that I get: 20,READ ERROR,01,01,0
    I do have the schematics.
    I have not checked the head's coil resistance. I will try to follow your directions to do so.
    I am using SD/DD disks, not HD.
    I have a logic probe and a multi-meter, no oscilloscope.
    What would explain that the directory/catalog commands have no effect on the drive?

  4. #4
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    Does the head ever move at all?

  5. #5

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    Quote Originally Posted by KC9UDX View Post
    Does the head ever move at all?
    Once I issue a header command, it seems that the heads move to track 0 but then they stay there and no longer move. Other commands such as collect will move the heads as well although the command fails.

    When I perform a header command on D0, it quickly fails and ?ds$ returns "75,format speed error,01,00,0". When I issue the command on D1, it takes a while longer to fail and ?ds$ returns "20, read error, 01,01,1". Any load"$",8 or dload"* I issue returns a file not found error code without any apparent access to the drive. Any directory or catalog commands do not return any error and don't seem to access the drive either.

  6. #6

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    Quote Originally Posted by retrobecanes View Post
    Here is the read error that I get: 20,READ ERROR,01,01,0
    I do have the schematics.
    I have not checked the head's coil resistance. I will try to follow your directions to do so.
    I am using SD/DD disks, not HD.
    I have a logic probe and a multi-meter, no oscilloscope.
    What would explain that the directory/catalog commands have no effect on the drive?
    Catalog or open15,8,15,"i0" should seek to BAM/Directory track, if that doesn't happen, I would check first the stepper logic and transistor drivers and of course have a look at the spindle speed.
    There must be tachometer images on the bottom of the drives and you need real "magnetic ballast" neon lamps or old incandescent lamp for speed checking.
    See here (me repairing a bad spinning 4040):

    https://www.youtube.com/watch?v=W5BBjIEiitY

    You better check the speed is not way off. The test should be done with a disk inserted.

    Frank

  7. #7

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    Quote Originally Posted by iz8dwf View Post
    Catalog or open15,8,15,"i0" should seek to BAM/Directory track, if that doesn't happen, I would check first the stepper logic and transistor drivers and of course have a look at the spindle speed.
    There must be tachometer images on the bottom of the drives and you need real "magnetic ballast" neon lamps or old incandescent lamp for speed checking.
    See here (me repairing a bad spinning 4040):

    https://www.youtube.com/watch?v=W5BBjIEiitY

    You better check the speed is not way off. The test should be done with a disk inserted.

    Frank
    Frank, I have been watching a few of your excellent videos and subscribed to your channel, very well done! I have tried to check the resistance between the different pins of the head connectors, and the one I have been testing has been between 10 and 30 ohms, but could you tell me exactly what resistance I should expect and this between which pins? I just want to make sure that I am doing this correctly. Also could you provide some instructions on how to check stepper logic and transistor drivers? I am not quite sure that you mean by that or which parts specifically need to be checked but I am all ears and I am eager to learn.

    D0 definitely seems to have a speed issue and I will disassemble it and attempt to adjust its speed based on the video link that you provided. However I am not seeing any controls or pots on the analog board to adjust it. The analog board that I have is PCB Assembly is #8250023 and D1 has a small board on top of it that I don't see described anywhere.

    I thank you in advance for your assistance in this troubleshooting.

  8. #8

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    Quote Originally Posted by retrobecanes View Post
    Frank, I have been watching a few of your excellent videos and subscribed to your channel, very well done! I have tried to check the resistance between the different pins of the head connectors, and the one I have been testing has been between 10 and 30 ohms, but could you tell me exactly what resistance I should expect and this between which pins? I just want to make sure that I am doing this correctly. Also could you provide some instructions on how to check stepper logic and transistor drivers? I am not quite sure that you mean by that or which parts specifically need to be checked but I am all ears and I am eager to learn.

    D0 definitely seems to have a speed issue and I will disassemble it and attempt to adjust its speed based on the video link that you provided. However I am not seeing any controls or pots on the analog board to adjust it. The analog board that I have is PCB Assembly is #8250023 and D1 has a small board on top of it that I don't see described anywhere.

    I thank you in advance for your assistance in this troubleshooting.
    Thank, first of all
    Well, every head has its own coil resistance, it is usually between 10 and 32 ohms, so as long it isn't much more, like kohms or much less like 1-5 ohms, it's ok. Now, also the way the various coil ends are connected on the actual connector and the wire colors varies, so the best you can do is try every combination, and you should get a "good reading", or consult your particular analog board's schematic where usually it's clear enough what pins are the RW coil and what is the Erase coil.
    The spindle speed circuit is usually located on a small PCB on the drive mechanics, it's also a part that greatly depends on what brand/model of drive you have. If I remember correctly, the 8050 and 8250 drives could use at least three different 100 tpi drive mechanics, so you have to identify what mechanics you have and find manuals and schematics for your particular parts.
    First you check that they are spinning at the right speed, you probably have to remove the drives from the chassis to access the wheel with tachometer images. Pay attention on what is the 50 Hz and 60 Hz one, depending where you live.
    You can't use CFL or LED lights for that. Only incandescent light or much better, magnetic ballast fluorescent tubes can show a clear still image.
    Or you can use a frequency counter on the right speed control chip's pin.

    Frank

  9. #9
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    I don't think this can be done with an incandescent bulb. The light output of at least every incandescent bulb that I'm familiar with has quite a bit of hysteresis. LEDs themselves work just fine for this, but not the consumer lighting kind with inbuilt power supplies.

  10. #10

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    Quote Originally Posted by KC9UDX View Post
    I don't think this can be done with an incandescent bulb. The light output of at least every incandescent bulb that I'm familiar with has quite a bit of hysteresis. LEDs themselves work just fine for this, but not the consumer lighting kind with inbuilt power supplies.
    It can definitely be done with an incandescent bulb, try yourself. The light ouptut is definitely periodic at 100 Hz (for a 50 Hz mains) with quite a bit of "DC" on it (i.e. the filament never completely estinguish). In contrast a magnetic-ballast powered fluorescent lamp is more like a square wave and goes down to a more lower light output every half mains cycle.
    I constructed a fast photodiode amplifier some years ago precisely to "watch" the ligjht output of various light sources. I can easily see the CFL switching cycles (mostly around 20 KHz for the ones I've tested).
    Frank

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