A non-working DAC bit will not change LEDs or switch settings.
It would only interfere with the DAC's ability to output all voltage levels.
That's analog voltages. The switches and LED's are digital. 0 or 1.
The DAC is not involved with reading or writing to them. The DAC is
used to set the voltage levels on the outputs of the 4051's. So if there
is a problem with the DAC swinging over the full range, then it will
affect those chips as well. I thought that was what you were describing,
but now I am not sure.
Op amps can fail in such a way that the input could always be at a constant
voltage, instead of being a high impedance input. So your 4051 output that
is stuck at 5V could be held there by a failed op amp, or more likely (IMO), the
4051 is bad.
ST is fed from a register chip on the KLM-366 board. I think it should be changing.
Did you look at it?
The 8048 reads the switches and saves their values in RAM when you save a patch.
In manual mode, it just reads them in and feeds them out again to the appropriate
places in the circuit. When you are using a patch instead, the values are read from
RAM and fed out instead of the current front panel switch states.
If all of the settings change at once, are you in manual mode at that time, or are you
using the patch setting from RAM?
Were you thinking that the tape circuitry would be active when you are not saving anything
to tape? Or maybe you tried to save patches to tape and found that those signals
did not change?
--------------------------------------------
On Tue, 8/30/16, 7zlwncpbis4x22jwvkd4oc5hzu2njcsjeup42is6@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:
Subject: [PolySix] Re: Trying to Restore a P6.
To: PolySix@yahoogroups.com
Date: Tuesday, August 30, 2016, 9:19 PM
Yes IC17, It just seemed strange to get a constant
5V on those outputs when it was part of the tape
circuit.And I have seen the pots track on all the
4051 outputs EXCEPT pin 1 on IC18, That sits at a constant
4.9VBut I will replace both 18 and 19 and use
machined sockets.And yes, using the x10 setting
on the probe. Understood about the
scaling.
What you describe
about missing bits sounds like what is happening. This is
what seems to set the synth off, and scramble all the data
in a patch. You can watch the program and bank buttons
change when that happens, as well as the write and manual
buttons, and see it on the scope from TP2 as
well.And I'm loathe to admit I have not been
able to figure out what "ST" is or does, but
I'd be glad to check it if you can tell me what switches
it.Thx.