Diagnosing the Atari 1050 failure

[Shift838]

I received an Atari 1050 drive from a lot I purchased.  The drive does not work.  It does power up.  It does not behave like my other 1050 when you power it up or put in a disk.

 

So, as soon as you power the unit up it does the expected, light comes on and drive gets immediately accessed.  But....  The drive disengages and about 2 seconds later it reengages, and light comes back on.  It does this constantly if it is hooked up to my 800xl or not.  You can hear the drive motor spinning but if you try to access the drive you just get the 138 Device does not respond error.

 

Has anyone seen this type of behavior before?  What should I be looking at?

[+Nezgar]

That's the POST failure mode. Something is not right that the firmware detected. First thought is track 0 sensor. I think I've caused this behaviour by disconnecting that. If you move the head all the way towards the centre of the disk and power up, does it step the head all the way back to the outermost track before doing the motor on/off cycling? If the track 0 sensor doesn't see the head "arrive" at track 0 this mode gets triggered.

 

CPU and ROM may be good since that repeating pattern is following ROM code. Next up it could be bad SRAM in the RIOT or 6810, which can be swapped out of another 1050 to test...

[Shift838]

17 hours ago, Nezgar said:

That's the POST failure mode. Something is not right that the firmware detected. First thought is track 0 sensor. I think I've caused this behaviour by disconnecting that. If you move the head all the way towards the centre of the disk and power up, does it step the head all the way back to the outermost track before doing the motor on/off cycling? If the track 0 sensor doesn't see the head "arrive" at track 0 this mode gets triggered.

 

CPU and ROM may be good since that repeating pattern is following ROM code. Next up it could be bad SRAM in the RIOT or 6810, which can be swapped out of another 1050 to test...

Moved the head to the center as suggested and turned the drive on.  Head never even tries to move.

 

 

[+Nezgar]

5 hours ago, Shift838 said:

Moved the head to the center as suggested and turned the drive on.  Head never even tries to move.

Ah k, so it sounds like your stepper motor isn't working. If you manually move the head to track 0 (outermost position) see if it powers up without the constant start/stop. This will confirm if your track 0 sensor is still working. If so, you may even be able to boot/read sectors from track 0 of a disk, until it tries to read another track.

 

Can you take a picture of where the wires from from the drive mechanism connect to the 1050 mainboard at the back left side of the drive? They may either be disconnected, or connected incorrectly. A picture would potentially allow us to identify an incorrect connection.

 

 

[+kheller2]

Or any of the other failures that trigger the same failure mode…. Please look at the 1050 FSM for the startup failures that trigger this mode.