Need Help with Disk ii Analog boards

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Last seen: 1 month 6 days ago
Joined: Apr 23 2022 - 18:41
Posts: 97
Need Help with Disk ii Analog boards

Hello group,

i have 2 disk ii analog boards that won’t read or let me check the speed so it’s clearly not writing either.  A good analog board the drive performs perfectly so this is an analog board issue. I’ve replaced the 4 ICs with known working chips. Checked for continuity from the actual leg of the chip in the socket to its destination along the trace and I don’t think there’s an issue with any of the sockets. Checked all the diodes and removed and tested the 4 axial caps. All good.  One of the 10ufs was showing about 30% above face value but I don’t think that is the issue.  The .22K cap at C6, and the Q1 and Q2 were removed and tested as well. I checked all the traces and if there’s anything wrong with one, I can’t find it.  I haven’t pulled and tested the 2 inductors at L1 and L2.

Any thoughts or input? 

Thanks group. 

MacFly's picture
Last seen: 9 hours 31 min ago
Joined: Nov 7 2019 - 13:49
Posts: 453
I guess the motor spins, and

I guess the motor spins, and the drive is alive - but you just cannot read? And you do not have an oscilloscope? The obvious next step would be to check along the signal path where the analog data signal is lost.

Apart from the things you already checked, another possible failure point is the two trimmers (R28/R33). They are glued/locked into position, which is a good thing. But it's possible that contacts corrode and trimmers fail. You could measure the resistance (total resistance and to the middle contact) and compare this with the working boards (they should not differ too much). It's also possible that a trimmer got bumped or other components degrade, so it's no longer at the correct setting. The service manual has a very detailed procedure on how to adjust them and how the signal should look at various test points. But you'll need an oscilloscope in order to do this procedure (And I wouldn't turn the trimmers unless you know you can follow the procedure to do the adjustment).

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