Do you get the blips when just holding one or more keys down
Or does it only make that sound right as you are pressing or releasing a key
What voltage do you measure at +5MEM
(on U164 pin 24)
If you have all of the data lines for U164 isolated from the bus, then there are
three more pins you can experiment with, trying to see which one affects
the blips. Leave the address and data pins bent out and isolated.
Chip enable (18)
Output Enable (20)
Write enable (21)
If you can figure out the exact signal that makes a difference, maybe we
can get a little further. It should be one of these three. Leave the power and
gnd pins connected. If you find the signal that makes the difference, then remove
U164 and connect a 22pf, 33pf, or 47 pf cap to gnd from that signal as an experiment.
You can just stick the leads into the socket temporarily.
You should get a similar effect. Of course it may take more than one of those signals
to cause the blips.
Bob
From:
"richtrix@... [oberheim]" <oberheim@yahoogroups.com>
To:
oberheim@yahoogroups.com
Sent:
Saturday, March 21, 2015 9:09 AM
Subject:
Re: [oberheim] Finding Clock frequency of my OBXa [2 Attachments]
[
Attachment(s)
from richtrix@... [oberheim] included below]
I don't know about the signal path to the lower board. I looked over the schematic for a minute but it wasn't overly clear. I'm not really experienced with digital electronics.
Last night I left the board on for a few hours and came back to it to see if it was acting weird. Everything was fine except I heard a couple isolated blips again in 5-8. They were still very infrequent when compared to having U164 removed. So whatever is causing these blips is more pronounced when something warms up. There must be something wrong somewhere. I've attached some small clip of u164 in and out to this message if you want hear what these blips sound like.