3 Sep
2011
3 Sep
'11
11:42 a.m.
I have made some progress with this problem and think I have identified a
faulty chip on the M9058.
Using my oscilloscope I verified that the control signals seemed OK so I
started to look at the Read signals to see if data is reaching the RQDX3.
Starting from the connector from the disk to the M9058 I could see a signal
quite easily, but then at the outputs of the 74LS158 (pins 4 and 7) that all
stops. This chip is used by all 4 disk channels, which explains why it did
not matter which channel I used.
It may be the chip, but what are the control inputs doing? Pin 15 is a
global enable to that chip, if it's high, the chip is disabled, and all
ouptus are forced high (IIRC). Often this is not used, and pin 15 is tied
to ground, but it's best to check.
Pin 1 selects between the 1 possible inputs for each multiplexer section.
Is this in the right state to pass the data through?
-tony