EQD Space Spiral doesn't do anything

[Maximiliaan]

Hey, finally got around to testing.

All the voltages remain the same as before except for pin 9 of LM324. That one is now at 4,33V.

Pin 13 and 14 of the PT2399 are still at 0V and 5,00V respectively.

The LFO is still doing nothing. I tried replacing the LM324 but still nothing. Any ideas what could be the problem?

[ElectricDruid]

OK, so we've got the following for the LM324 volages, right?:

LM324:
1: 4.32V; 2: 3.85V; 3: 4.32V; 4: 8.64V; 5: 4.23V; 6: 4.32V; 7: 4.33V
8: 4.22V; 9: 4.33V; 10: 4.23V; 11: 0.00V; 12: 4.12V; 13: 4.21V; 14: 4.21V

Or with the function, instead of the pin number (since we don't know which amp is which):

O: 4.32V; -: 3.85V; +: 4.32V; +V: 8.64V; +: 4.23V; -: 4.32V; O: 4.33V
O: 4.22V; -: 4.33V; +: 4.23V; -V: 0.00V; +: 4.12V; -: 4.21V; O: 4.21V

And here's the LFO circuit, separated out:


Basically, all those voltages look pretty good now. The thing seems to be biased up like you'd expect. So, if it's not actually oscillating, we need to look closer. The two op-amp stages on the left are the actual LFO part. IC5.2 is a comparator and should have a square-wave output on its output. IC5.1 is the integrator and should have a triangle on its output. If no oscillation is going on, there's something wrong on one of those two parts.

We need to find which op-amp section the C30/10n cap is connected to to identify the comparator, and which op-amp section C28/1u is connected to to identify the integrator.

Once we know which bit is which, we can test the LFO circuit. Take the LM324 out of the socket - we're assuming it's good and testing the rest of the circuit. We need to make sure that there's a solid connection from the integrator output back to the comparator +ve input. It should read 33K/R28. We can also test that we have the expected 47K/R26 between the output and the +ve input for the comparator.

We can also set the Rate pot to max and test between the output of the comparator and the -ve input of the integrator. That should give us R22/33K. We can test from the integrator output to ground, and we should see the pot value+10K, so 1010K, roughly (pots are often +/-20%, and 10K is only 1% of 1Meg).

If all those are right, the LFO should be working (especially with those voltages) so we're expecting that there's something wrong there somewhere. The question is which one!

Once we've got that part working, we can see if the last two stages are ok. Hopefully it will just spring to life...you can dream, right?!? 

[Maximiliaan]

Thanks for all the info!

I went over the vero board layout and IC5.2(the comparator) corresponds to pin 1, 2 and 3 on the vero.
IC5.1(the integrator) corresponds to pins 5, 6 and 7.

So I tested integrator output to comparator +ve input (pin 7 to 3) and it reads 33k, so check there.
The comparator output to +ve input (pin 1 to 3) reads 47k, so also check.
With rate set to max, from comparator output to integrator -ve input (pin 1 to 6) reads 33k, check.

Now, the last part I don't understand. I don't see a path from the integrator outpot to ground on the schematic, and also don't measure any resistance there. I mean, my dmm just maxes out there. Could the fault in the circuit be there somewhere?

Thanks again for all the help!

[duck_arse]

the pot shows on the circuit as being connected to V/2, whatever they've called it. it should read pot+stopper resistor+47k in the lower leg of the dvider, to ground. find that divider pair R24 and 25 on the schem, check their connections.

[ElectricDruid]

Now, the last part I don't understand. I don't see a path from the integrator outpot to ground on the schematic, and also don't measure any resistance there. I mean, my dmm just maxes out there. Could the fault in the circuit be there somewhere?

No, sorry, my bad. It's from the *comparator* output to ground. The Rate pot and resistor are connected to the comparator output, not the integrator. What can I say? It must have been late...

Glad the other stuff looks good though. That's promising, at least.

[Maximiliaan]

Hey,

I tested and it all looks fine. Also tested all the connections and resistance values for the other two opamps and everything is as it should be. Still not working though, unfortunately

Is there any other test I could do? I'm about ready to abandon this one I think. First pedal I ever made that really doesn't want to work, haha.