New Revibe: done! Needs fixing!

[SleepLess]

Hi there!
When I finished my first Revibe at the end of last summer and let some friends of mine play it, one instantly ordered one from me! He's a long-time friend and despite the time involved in building a Revibe, I couldn't help but say yes. I finished it up yesterday and unfortunately the tremolo isn't working. The LED lits up fine but doesn't blink, it stays full on all the time. I don't have any tremolo effect no matter the pot settings or slow/fast switch. The good thing is that the reverb works perfectly. I would need you guys' help to solve this issue. I'm sure it's nothing much but I just can't seem to figure it out...

Here are three pictures. You'll notice I didn't use a turretboard on this one but an eyelet board. On the previous build I used carbon film resistors and found the Revibe to be a bit noisy so I chose metal films on this one.

Thanks for your help in advance !

[sluckey]

Need voltage readings for V5B.

There should be one continuous ground jumper that starts on the top left side of the board and continues about 2/3 of the way across the top of the board. That chain looks broken to me. Did you put some jumpers under the board for that?

While troubleshooting, temporarily replace the LED with a 4.7K/22µF. They'll fit on the board where the LED wires connect. This will eliminate the LED as the problem.

[shooter]

my guess is the trem isn't oscillating.  go over all the R's in the trem, with a meter and make sure they are correct values, the metal film color coding gets confusing.  I circled a .022 cap that looks like it got burnt n bubbly?

[SleepLess]

Need voltage readings for V5B.

Thanks guys!
I'm in the EU, if you spot any strange  readings...

V5
pin 1: 222V
pin 2: oscillates betwwen 37mV and 40mV (depth and intensity on 0)
pin 3: 1.9V
pins 4/5: 3.2VAC
pin 6: 161V
pin 7: 0V
pin 8: 1.83V
pin 9: 3.2VAC

All these readings were taken with the LED still in.

There should be one continuous ground jumper that starts on the top left side of the board and continues about 2/3 of the way across the top of the board. That chain looks broken to me. Did you put some jumpers under the board for that?

The continuous jumper ground is there, it just goes up and down on the board, it was much easier to do.

While troubleshooting, temporarily replace the LED with a 4.7K/22µF. They'll fit on the board where the LED wires connect. This will eliminate the LED as the problem.

WIll do that too!

Shooter I will also check that cap but it looked good before installing it (and it already had that small burn).

[SleepLess]

I disconnected the LED and replaced it with the 4.7K/22uF pair and the vibrato is still not working...

[sluckey]

OK. Leave the resistor and cap in until it's working. Verify every component value in the V5B circuit (ain't that many) and verify that all jumpers are correctly installed in that part of the circuit too. Don't forget to verify front panel components including the speed pot. The intensity pot will not keep the oscillator from working. Since you don't have a blinky LED right now you can tell if the oscillator is working by monitoring the voltage on V5 pin 6. It will be steady if not working. It will be constantly changing (appears erratic on a digital meter) if it is working.

Keep looking. It's gonna be something simple and it's got to be in the V5B circuit.

[SleepLess]

OK, fixed issue! I had a 1M resistor that was shot, the one that sits between the two .01uF caps. It was measuring 2M and then was going way above that to 16M! Replaced it and now the tremolo is working. I find it to be a bit weak though. You can start hearing it on 5 on the intensity pot, but below that you can't. I had fun playing with the trem on 4 and clicking it off via the footswitch and it's the same... Is there a value to change somewhere to make it stronger? Or will soldering the LED back in place make it stronger?

Thanks Sluckey for your help (and shooter as well!)!

[sluckey]

Or will soldering the LED back in place make it stronger?

Yes it will. Put it back in.

While you are plundering around the trem oscillator circuit, make note of what the voltage readings look like. Change the speed too. If you have a true RMS voltmeter set it to measure AC volts and look at V5 pin 6. Also look at the hot side of the intensity pot. Vary the speed pot and see how much the meter reading changes. Write these numbers down on your schematic for future use. (See the green note on my schematic?)

All phase shift oscillators work in a similar manner. The knowledge you gain from this circuit will help you analyze most any other tremolo oscillator circuit.

[shooter]

Glad you're working! It is a nice sounding unit - even for a non-musician like me!