3 Mar
2014
3 Mar
'14
8:37 a.m.
Another quick update:
I got a personal Email from David Humphries, where he explained the
modification to eliminate the transient that causes a false increment of
the Current Address Counter in the RK8E disk controller.
The modification is quite simple - piggybacking a 7474 (dual D
edge-triggered flip flops) onto one of the chips that is involved in the
generation of the clock pulses for the Current Address Counter
(piggyback is only for power), and then patching one of the flip flops
into the circuit to latch the TP3 signal to prevent it from going low
before the signal that is the decode of the DLCA (Load Current Address
Counter) IOT instruction de-asserts. On David's RK8E with similar
symptoms, this modification prevents the spike from occurring, and will
hopefully serve as well to fix the issue I've had with my RK8E.
I am going to make this modification to the M7105 board today, and will
post the results as soon as I can.
Thanks to David for digging through his notes to recover the information
on the modification that cured the problem he was having with his RK8E
and sending it to me.
If anyone wants the procedure for the modification, I can Email it to
you. Just drop me an Email and I'll send it along.
Best to all,
-Rick Bensene