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]

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]

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]

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]

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

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!



On with the testing and calibration!

[wendallsan]

Tested and calibrated! Thanks again!

On to the filters!

[MuadMusic]

I have built out a 706 circuit. I all works, but the "delay" seems to do nothing.
1) what is it supposed to do? delay the onset of the lfo after a gate?
2) if so, what would that be useful for?
Also,
3) I don't have the on/off switch installed yet, just a direct connection to the gate jack. do I just wire the output of the jack to one pin of the switch, then route the output of the switch to the Gate in on the pcb?

thx

[wendallsan]

That is a very good question! I checked the System 700 manual for the original modules and it looks like the LFO is connected to the keyboard so that it is triggered when a key is pressed, resetting the LFO. The delay is supposed to delay that trigger for the LFO reset, but there isn't an input on the module for the trigger input. So I also don't know what it's supposed to do in this case, and I honestly thought it was a 2nd LFO frequency CV input until I squinted at the panel label and saw that it was not labelled as such.

How about that wacky wiring on the LFO shape selection switch?

[MuadMusic]

Thanks for the response!

One other question. I've tried to do the calibration per the Pharmasonic instucions. Something seems off. here are the symptoms:
I can do the first adjustment of the sawtooth offset but ...
The triangle is skewed. It does not reach the peak before the reset so there's a sharp jump to the peak at reset.
The sin wave is not really symmetrical either (since it is derived from the triangle.
I can fix the triangle symmetry by adjusting the sawtooth offset but ...
Neither sin nor triangle is centered on ground It's more like +5 and -2v

Any ideas?

[MuadMusic]

p.s., very cool project of yours!

[wendallsan]

Thanks for the response!

One other question. I've tried to do the calibration per the Pharmasonic instucions. Something seems off. here are the symptoms:
I can do the first adjustment of the sawtooth offset but ...
The triangle is skewed. It does not reach the peak before the reset so there's a sharp jump to the peak at reset.
The sin wave is not really symmetrical either (since it is derived from the triangle.
I can fix the triangle symmetry by adjusting the sawtooth offset but ...
Neither sin nor triangle is centered on ground It's more like +5 and -2v

Any ideas?

I think I had asked about this as well when I was working on my modules, and I think the response was that some of the waveforms were strictly in the positive voltage, while others were positive and negative. So that much is probably actually correct. Here is what I had reported in my thread (from viewtopic.php?f=17&t=221957&p=3123006&h ... 6#p3123006):

The voltages output by the various waveforms don't seem consistent in their high and low voltages. The SQU and SAW seem to be more or less all positive voltage while the TRI and SIN seem to be passing through positive and negative voltage. Here are my current readings:

7.01 +0.14 squ
7.78 -0.45 saw
+5.9 - 4.7 tri
+5.2 -4.7 sin

I would need to revisit my modules again with a scope to see how 'triangle-y' and 'sine-y' the sine and tri settings are on my module, but I don't recall having any difficulty getting what I thought looked like reasonable waveforms for those settings with my modules.

I wound up getting a 4MS SISM module to handle offsetting and scaling CV signals to the ranges I wanted them in.

Glad you liked my project! It is an amazing synthesizer and was worth the time and money to build, for sure. Best of luck on your builds!

[wendallsan]

Here are shots of what my 706 is outputting for sine and triangles. The bottom of the sine is a little pinched but otherwise these look pretty dead on to me.

[MuadMusic]

Again, very helpful.
BTW, I got a helpful response from Ori at Pharmasonic regarding what the delay is designed to do.:

the Delay is a sort of fade in effect.
You could achieve the same effect by controlling the output of the LFO with a VCA that is controlled by a simple enveloppe like a slope generator.
The original circuit from the System-700 is desig
ned for a 10V (or more) trig/gate.
I adapted the circuit for a 5V trig/gate since it's more common these days especially in the eurorack world.
So, if you use a trig/gate above 5V it may not work properly.
That being said, you can also refer to the Section 5 of the System-700 manual for the calibration if you prefer.

[MuadMusic]

one other question. There is a trimmer (VR9) that shows up on the component side of the PCB in this picture, next to the CA3080.

My question is "did you install this on the component side or on the back side with the power header and all of the other trimmers?

[MuadMusic]

I've answered my own question. The board has been revised since the documentation was created. The PCB labeling shows clearly that this trimmer is on the back side with all of the other trimmers.

[wendallsan]

Sorry I didn't get a chance to respond sooner, but glad you got an answer!

[dragon22]

saving this post. cheers