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Help me troubleshoot MY OTHER Pharmasonic 706
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Help me troubleshoot MY OTHER Pharmasonic 706
wendallsan
Hi all,

I am now looking at my 2nd LFO and hoping to troubleshoot it. I made a happy accidental discovery tonight which I hope will help to troubleshoot it, rather than starting from a simple 'it doesn't seem to do anything when I plug it in.'

I was doing some due diligence tonight in going through my last post and trying out everything there to see if I could resolve anything myself based on the help that was provided there, which meant unpluggind and plugging things back in on the boards and faceplate on the module while I did my testing. I accidentally failed to plugin in the one-wire jumper that goes from the top to the bottom boards, and suddenly the LFO began working. So it seems to work without this wire in place. I haven't attempted to calibrate it, as I'm sure that wire is there for some reason, and I figure I should troubleshoot this before moving forward with calibration.

Please let me know where I should begin to troubleshoot this module with the current behavior in mind.
guest
so it works when the wire is NOT in place, but doesnt work when the wire is in place?
wendallsan
guest wrote:
so it works when the wire is NOT in place, but doesnt work when the wire is in place?


Yes. Weird, right?
devinw1
So is that 1x8 connector near the power the bus between the top and bottom PCB? Seems weird there's 1 separate wire connecting them separately, unless that was an afterthought.

Is there a schematic available for this version?
wendallsan
devinw1 wrote:
So is that 1x8 connector near the power the bus between the top and bottom PCB? Seems weird there's 1 separate wire connecting them separately, unless that was an afterthought.

Is there a schematic available for this version?


The connection isn't the header by the power bus, but is at the top of the bottom board. See the image below-- the yellow line is drawn between the two points that this wire connects:



The header down by the power bus plugs straight into the header on the top board, so there is no strange wiring involved there.

No schematics are available as far as I know. Yes, the LFO's have a pretty wild configuration of wires between that 4-way switch, a panel-mounted 16mm pot, and the other wiring involved. It is certainly the most complex in the series as far as off-board connections go.
guest
that line should be -12V. what is the voltage when the jumper is in place? its possible there is a short on the top board which is pulling that line to ground. also, can you post pictures of this build?
wendallsan
guest wrote:
that line should be -12V. what is the voltage when the jumper is in place? its possible there is a short on the top board which is pulling that line to ground. also, can you post pictures of this build?


The wire in question is indeed reading -12V, so things look good that far along the line ...

Pics are uploaded at:

Top Board Front
Top Board Back
Bottom Board Front
Bottom Board Back
Top Board Connections
Bottom Board Connections
guest
ok, so it sounds like it might be an issue with the trigger circuitry. is it oscillating? is there a signal on pin1 of IC1?
guest
does anything come out of it if you turn VR9 to its extreme (try both ways)?
wendallsan
guest wrote:
ok, so it sounds like it might be an issue with the trigger circuitry. is it oscillating? is there a signal on pin1 of IC1?


It seems to be oscillating. Here are the voltages relative to ground for the pins on IC1, with "Variable" meaning the voltage is changing over time (oscillating):

1 Variable
2 0
3 0
4 -12
5 Variable
6 0
7 0
8 Variable


Quote:
does anything come out of it if you turn VR9 to its extreme (try both ways)?


Which pot/trim is VR9? And so I know in the future, how do you determine the order of parts (VR1 vs VR9) on boards that don't have them labelled as such? I see on the LFO boards that IC1 is labelled as such, but I'm not seeing any such labels for pots or trims.
guest
sorry, i was looking at the PCB on the pharmasonic website, and it looks like yours is a different rev. with different labels. turn the OUT trimmer.
wendallsan
Haha, thanks for explaining that!

Sure enough, turning the OUTPUT trim brought up the levels and I now have a signal coming out of the module! Thanks very much for suggesting that!

we're not worthy we're not worthy we're not worthy

On with the testing and calibration!
wendallsan
Tested and calibrated! Thanks again!

On to the filters!
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