MOUNTing Problem

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Re: MOUNTing Problem

Postby AltairClone » June 4th, 2019, 7:03 pm

Most of the 55-GFR drives have a 1K SIP resistor pack permanently soldered into each drive. Termination is not what you were up against.

In making a first guess, I'd say your two drives are aligned slightly different. I assume you wrote the disks using the original drive 0? Drive 1, with a slightly different alignment, may have a hard time reading disks written by drive 0. Until the FDC+ has spun a few revolutions of drive 1 to establish timing parameters unique to drive 1, it has to use nominal values for timing. However, the first mount attempt on drive 1 has already failed by the time the FDC+ has gathered data for the drive. By the second time you try it, the mount works because the FDC+ has made a slight adjustment for drive 1's timing that is just enough adjustment to allow it to read the disks.

Here's an experiment:

1) restore the original configuration and duplicate the failure.
2) use PC2FLOP to write the disk image you're using in drive 1, but this time, actually use drive 1 to write the disk.
3) re-run the test of step 1 and see if the problem changes

Mike
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Re: MOUNTing Problem

Postby toml_12953 » June 5th, 2019, 7:09 am

AltairClone wrote:Most of the 55-GFR drives have a 1K SIP resistor pack permanently soldered into each drive. Termination is not what you were up against.

In making a first guess, I'd say your two drives are aligned slightly different. I assume you wrote the disks using the original drive 0? Drive 1, with a slightly different alignment, may have a hard time reading disks written by drive 0. Until the FDC+ has spun a few revolutions of drive 1 to establish timing parameters unique to drive 1, it has to use nominal values for timing. However, the first mount attempt on drive 1 has already failed by the time the FDC+ has gathered data for the drive. By the second time you try it, the mount works because the FDC+ has made a slight adjustment for drive 1's timing that is just enough adjustment to allow it to read the disks.

Here's an experiment:

1) restore the original configuration and duplicate the failure.
2) use PC2FLOP to write the disk image you're using in drive 1, but this time, actually use drive 1 to write the disk.
3) re-run the test of step 1 and see if the problem changes

Mike


This is what I tried: After BASIC loaded and all initialization questions answered, I switched floppies so that the Games floppy was in drive 0 and the BASIC interpreter floppy was in drive 1.
Then I typed MOUNT. MOUNT with no parameters gave no errors. I might get to tear it all apart today some time and restore the original config.
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Re: MOUNTing Problem

Postby toml_12953 » June 9th, 2019, 11:07 am

I put everything back the way it was and guess what! No problem now. Maybe there was dirt on the connectors and moving them around cleaned the contacts?
I don't know but since it works and I can't make it NOT work, I'm satisfied. Thanks for the suggestions!
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Joined: June 7th, 2013, 12:54 pm

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