Re: Need help with dead Disk II drives

[Rubywand <rubywand@swbell.net>]

Bob Danielson writes ...
> 
> They chatter for about three seconds when first powered up , then just
> merrily spin along indefinitely with no attempt to find the boot
> sector on the diskette.
> 
> Is there anything I can try at home before biting the bullet and
> trying to buy replacements?
>

     You could try some tests; but, they're more trouble than the fix
tries, so we'll just cut to the chase.

     Basically, it sounds like Drive 2 does not know when to stay OFF.
There are three fairly high-probability places where a glitch may cause
this to happen:

 1. The 74LS132 on the Disk ][ Controller card may have a blown gate or
some pins may be making poor or no contact. Try unplugging and
re-socketing the IC. This usually takes care of bad contact problems.
(Or, you can replace the 74LS132 IC with another 74LS132 or 74132. A
74LS00 or 7400 may work, too.) Also unplug and re-socket the 9334 and
556.

 2. The ULN2003 IC on the Drive 2 main circuit board may have a bad gate
or may have developed some poor pin-to-socket contacts. Remove the drive
cover. Unplug and re-socket the ULN2003 IC. (Directly replacing a blown
ULN2003 could be difficult. If you do not mind doing some rewiring, a
couple 7404's should get the job done.) 

 3. Drive 2's cable may have developed a short between pins 14 and 16.
Mark the position of the cable at the Controller card and at the Drive 2
circuit board and unplug the cable at each end. Use an Ohm meter to
check for shorts between adjacent pins. If you find a short between 14
and any other pin you can try repairing the cable or cutting out line 14
and running a new lead; or you can get a replacement cable.

 
Rubywand