Check for continuity from KLM-367/IC34/pin3 to KLM-366/R23.
Or measure the voltage on KLM-367/IC34/pin3: it should be around 0V for
VCA EG mode and around +5V for VCA Gate mode.
Is the Effects Mode switch working? The control bits for the Effects
Mode are on the same latch as the VCA Mode.
The programmable attenuator is done with latch IC35. There is a low
quality 4-bit D-A converter built with IC35 and R94..R97. This voltage
(16 steps) is then fed to KLM-368 where the overall VCA sits.
Check continuity KLM-367/R94 - KLM-368/R185.
You can check with the DVM (voltage mode) if the voltages on the outputs
of IC35 change (pins 2, 10, 1, 11).
But it might be that this latch cannot be written by the CPU (Effects
Mode would be dead as well): check continuity IC34/pin5 - IC35/pin5 -
IC22 (CPU) / pin36.
Good luck!
Johannes
On 2015-02-16, 18:14 Joel Dalton joeldaviddalton@gmail.com [PolySix] wrote:
>
>
> Hi everyone!
>
> I'm excited to join this group. It seems there is a wealth of knowledge
> here about this great instrument!
>
> I thought it best to tackle one issue at a time instead of one big
> post. Long story short, I fixed the open traces caused by battery
> damage (battery had already been replaced) and replaced IC31 and that
> fixed most issues. I can now store patches and most of the erratic
> behaviour is gone. However, the VCA mode switch and attenuator don't
> work. At first, the VCA was always controlled by the EG, then after a
> couple reboots it seems to be stuck in gate mode. Seems like a problem
> with the logic circuits. After reading a previous thread in this group,
> I checked the effects board for damage and it looks clean (the effects
> don't work, but I'm tackling issues one at a time, as it's likely the
> same thing could be causing both problems). It seems like the control
> signals for VCA mode/attenuator travel on D02 and D03, and make their
> way through the same logic chips that reside near the "battery of
> death". Maybe there are PCB traces that I missed? I checked for
> continuity and used jumpers to fix the open traces. Is it possible that
> a logic chip could be partially dead? Also, am I correct in thinking the
> VCA mode would be stored as a binary value and the attenuator as a
> control voltage? I'm not sure how all these parameters are stored, are
> CVs all passed to an ADC and stored as 8bit values in ram? In Manual
> Mode, is the same logic circuitry used, simply ignoring values in ram?
> I've looked over the schematics and signal flow diagram but I'm still
> trying to wrap my head around the way the analog and digital circuits
> work with each other. I have a basic understanding of logic circuits and
> analog circuits from college, but I'm in over my head here....
>
> Anyway, sorry for the barrage of questions but I'd really appreciate
> some insight here. I have a DVM and a scope is on its way. Thanks a lot
> for reading!
>
> Cheers
>
> Joel
>
>
>
>