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Thread: Fixing a RX02 drive

  1. #11
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    Unless you've taken the drive apart, the likelihood is that there was nothing wrong with your drive's alignment in the first place. I trust that you marked the original position of the Track 0 sensor.

    What happens is that dust or dirt obscures parts of either the LED or the sensor and alignment is affected by a few milli-inches. The remedy is to clean the sensor.

    The Calcomp drive, being a leadscrew-type positioner should be extremely stable over time.

    Short of scrounging a real alignment disk, about the best you can do is to use a known-good conventional disk.

  2. #12

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    Quote Originally Posted by Chuck(G) View Post
    Unless you've taken the drive apart, the likelihood is that there was nothing wrong with your drive's alignment in the first place. I trust that you marked the original position of the Track 0 sensor. What happens is that dust or dirt obscures parts of either the LED or the sensor and alignment is affected by a few milli-inches. The remedy is to clean the sensor. The Calcomp drive, being a leadscrew-type positioner should be extremely stable over time. Short of scrounging a real alignment disk, about the best you can do is to use a known-good conventional disk.
    The optical sensor is what I have cleaned in the first place off course... Also cleaned the metal piece which is
    used to enter the optical sensor. Also connected the drive to port 0 to be sure that there was no electronic problem.
    But the problems persists. And off course I have marked the original setting. After these steps I carefully turned the
    screw a bit and it made a huge improvement...

    When I got the drive, the connector was disconnected and a paper was inside the drive with the note that drive 1 was broken.
    So I have no idea what else was done to the drive in the past. But they have worked on it for sure...
    WTB: Case for Altair 8800 ...... Rolands Github projects

  3. #13
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    That's too bad--I stated what I did because too often, some enterprising person will diagnose an "alignment error" and attempt to remedy it--when the situation was only that the sensor was dirty. I use 8" drives that are well over 40 years old that have never been re-aligned--and the alignment is bang on.

    There are alignment instructions for the standard Calcomp 140, but the RX02 with its custom electronics likely has its own maintenance procedure. I can't help you there.

  4. #14

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    Hi Roland. You directed me here and I feel compelled to add something. You need to find an 8" alignment disk. I have a Dysan one but I can't imagine a circumstance where I would loan it out unless I was present. The way it works is there is a track you position the drive to and then look at the output of the head amps. There is a cats eye pattern recorded on the adjacent tracks so you see perfect eyes on the scope when the drive is aligned. After you have done it once there is nothing to it. Barring that you could try writing on a good drive 2525 or 5252 octal patterns on a track and write the adjacent tracks to all zeros. Look at it on a good drive so you know what you are supposed to see. I think those are the max frequency patterns. Or else it is 7777's and I am thinking of hard disk encoding. Center the head where the pattern looks the best. There could be something wrong with the head as well.

    Hope you can find an alignment disk. Really handy things to have when you need them.
    Doug Ingraham
    2nd owner of Straight 8 SN1173
    5 other PDP-8's including an 8/i and a DECSet 8000
    SOL-20

  5. #15

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    Hi Doug,

    Quote Originally Posted by DougIngraham View Post
    ...You need to find an 8" alignment disk...
    Yes it seems to be... To be honest I got the drive working quite well in the end. But an alignment disk would help also with other drives. I'm afraid that I can't make an official alignment disk by myself. I think the pattern is similar to a RK05. But just some specific known data on a track would help I guess.

    Quote Originally Posted by DougIngraham View Post
    Barring that you could try writing on a good drive 2525 or 5252 octal patterns on a track and write the adjacent tracks to all zeros. Look at it on a good drive so you know what you are supposed to see. I think those are the max frequency patterns. Or else it is 7777's and I am thinking of hard disk encoding. Center the head where the pattern looks the best. There could be something wrong with the head as well.
    That is what I was thinking about too. The best would be that the disk is fully wipedand have a known pattern at a known specific track. But I'm not an disk expert to know that kind of pattern I should write to see a specific pattern at the oscilloscope...

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  6. #16
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    Roland,

    What you can do is to check the alignment through your 8"on the PC.
    With ImageDisk 1.17 or 1.18 you can check the alignment.
    Bit long ago but the number is a indication on how accurate the alignment is.
    The bit pattern in that case is not important.
    Also you see that the format pattern is E5

    ImageDisk-Screen.jpg

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