Oakley Dual-LFO Issues

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sonoresstudios
Learning to Wiggle
Posts: 5
Joined: Sun Nov 01, 2020 7:21 am

Oakley Dual-LFO Issues

Post by sonoresstudios » Tue Nov 03, 2020 1:50 pm

Hi,

I have recently finished two Dual-LFO's. One is working perfect, the other doesn't.

The second one acts weird in a "random" kind of way,

Example 1:
When I have the pots in mid position, LFO 1 behaves normal.
LFO 2 is muuuuch slower, when I increase the rate to go faster...it goes faster, then going to mid position it has the same speed as LFO 1.

Example 2:
same as example 1, but when going to mid position again, it doesn't switch. When I measure pin 7 on the TL072 it doesn't switch btw pos and neg voltage. This could also be the case for the LFO 1, hence the "random" behavior.

Sometimes when I apply power the LED just light up, it doesn't switch...then I need to rotate the pots and it start switching, sometimes normal, sometimes "random". The Shape pots kinda acts the same, it can get the switching started or stopping.

When I gently bend the PCB it sometimes start working normal, sometimes not...my first check was for faulty soldering joints or loose components etc. I have also switched the jacks connection cables btw the working module and the "not normal" working module. No change.

The thing is, I built both of them at the same time, measuring all resistors and caps before soldering. The only component that differs from the schematic (that I found) is C5. Schematic says 100nF, BOM says 47nF. I went with 47nF since it works in the first one.

Any ideas?

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Synthbuilder
Super Deluxe Wiggler
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Location: Cumbria, UK

Re: Oakley Dual-LFO Issues

Post by Synthbuilder » Wed Nov 04, 2020 5:50 am

sonoresstudios wrote:
Tue Nov 03, 2020 1:50 pm
When I gently bend the PCB it sometimes start working normal, sometimes not...
If it is intermittently working when you flex the board, then the fault is almost certainly a poor connection somewhere. It is most likely a bad solder joint, but it could also be a broken connection inside one of the pots, or an IC socket not making contact with the inserted IC.

The first thing to do is measure the power pins on the two TL072 ICs. Make sure that pin 8 is +15V and pin 4 is -15V. Measure the voltages with respect to the power supply's 0V terminal at the power supply or the distribution board.

If you've checked carefully the solder joints then remove the board from the panel and gently wiggle the pots and see what happens. It is possible that the brown part of the pot has been damaged and an internal connections broken. Sometimes it is even possible to see a small crack in the brown section around the pot pins.

Also remove all the ICs and push them back into their IC sockets.

sonoresstudios
Learning to Wiggle
Posts: 5
Joined: Sun Nov 01, 2020 7:21 am

Re: Oakley Dual-LFO Issues

Post by sonoresstudios » Thu Nov 05, 2020 12:29 pm

The TL072 voltages seem to be correct.
Gonna check the pots as soon I have time!

Thank you Tony for the support...

sonoresstudios
Learning to Wiggle
Posts: 5
Joined: Sun Nov 01, 2020 7:21 am

Re: Oakley Dual-LFO Issues

Post by sonoresstudios » Tue Nov 10, 2020 2:15 pm

The Shape 2 pot was broken (loose contact) first time ever for me. I usually don't measure the pots, I will from now on.

Again, thank you!

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