To save time, bend out all 8 data bus lines, and install U164 with no data bus
connections.
Then bend out all of the address too if it still is fixing the issue.
If that breaks things again, bend back half of the address lines.
Then try the other half. Sort of a binary search instead of bending in and
out pins one at a time, which could take a lot longer.
Always keep the power and gnd to this chip connected. Also, the chip
select pin should be connected as well. Assuming the chip is not actually
being used, disconnecting address or data lines should be OK. But not the
power pins or the chip select/ chip enable pin.
Bob
From:
"richtrix@... [oberheim]" <oberheim@yahoogroups.com>
To:
oberheim@yahoogroups.com
Sent:
Thursday, March 19, 2015 6:25 PM
Subject:
Re: [oberheim] Finding Clock frequency of my OBXa
Thanks again Bob,
I am not going to worry about the memory problem right now as I've gone back to the midi kit for control. I got my oscilloscope in and was able to compare waveforms. I got a +5V offset 500 KHz wave on pin 6 for both stock and the Midi Kit. They looked pretty close to identical. The strange thing is that I sort of fixed the Blipping problem. While switching between stock and the MIDI kit I got sloppy wanting to play with my new oscilloscope toy and forgot to remove the stock ICs besides the Z80 which is required for the installation of the Midi kit. Well when I turned it on it sounded fine... No blips or nothing just like when it was stock. I scratched my head wondering why the hell it was working fine now when I realized I had left the ICs in. Happy that it didn't catch fire or something and seemed to be working fine despite this I began removing one chip at a time to see if I could isolate something there. I ended up finding the one chip which if removed would begin the blipping. U164 the CMOS chip, if left in place, eliminated the blips. If removed they came back.
Anyone here have any idea as to why this might be
I have tested all crucial functionality and everything seems functional with the midi kit. Sysex dump and read, MIDI in and out all function well. I have not tested everything but those important things are fine.
I really don't know what it means for the system to leave in U164 along with the Midi Kit. What I have experienced is that after an hour or two of being on the lowest octave keys began to act weird. Delayed notes on keypress or on holding down a key producing a repeating note on every second or so. This was cleared up with a cycle of the power but I imagine somehow the CMOS is starting to conflict with the Midi kit. Any theories why the CMOS would smooth the blips out though
if I could keep that function but ditch any higher function that might conflict (by bending out pins maybe) That'd be perfect.
Sincerely,
Rich Clarke