Lowrey TLO vibrato not working.

[human-potato_hybrid]

My TLO vibrato has either worked very faintly, or not at all. However, it did sound fine when it did work. Do you think the 8mF capacitor (connected to Q2 E, see schematic below) has gone bad? All of the capacitors look good to the eye. Unfortunately I have neither a capacitor tester nor oscilloscope, but I verified that the board is getting power (14.9V) and it looks good visually. Capacitor is the black tube near bottom, larger than others.

Sorry for poor schematic quality that's all I have.

[human-potato_hybrid]

I originally called this post "reverb" not "vibrato". Long day at work, haha.

[human-potato_hybrid]

I went through and measured the voltages of the circuit with my voltmeter as shown. I measured these with all stops "on" (On, Fast, Heavy) to match the schematic. Out of curiosity, I also set the vibrato to "Slow". The voltages on either side of the "8" capacitor were then 2.3 and 8.8, expected, since the Slow setting shorts a 4.7k resistor. Of note, the voltages were steady over time. Even though I was using a voltmeter, I would expect the output to vary when the vibrato effect is on.

FYI I made sure to have good contact on all points. All measurements were repeatable.

Thanks guys!

[you795a]

Just a shot off the wall here. I had a TLO-K. If I recall correctly when the glide switch is activated I think it might disable the vibrato.

[human-potato_hybrid]

That's correct, but unless there's a significant problem with the glide switch or wiring, that's not what's happening. Though I'll unplug it to check.

[human-potato_hybrid]

I tested out the identical vibrato board on my TLO-1 and it gave me the voltages in green. Anyone have a guess on what component might be bad to cause the (steady) voltages in red on the other board?

[Larason2]

I would say there is a problem with the vibrato oscillator part of the circuit. Hard to say which component it is though, there are 3 caps and that transistor. Anyway, one or more of them are probably faulty, so that is why the circuit isn't producing the oscillations, which kind of works like an analog tone generator. I would start with the caps, they don't look like very high value ones. Make sure that all of the variable resistors have also been cleaned with fader lube.

[human-potato_hybrid]

Yeah I got some caps ordered. We'll see what happens :)

[tucsondave]

You can easily check the caps for shorts with an ohmmeter. If no shorts then jumper one at a time with a similar value cap. Anything in the range of 1 to 5 mfd should start the oscillator if only one is bad.

td

[human-potato_hybrid]

Thanks Dave, that's exactly my plan. I ordered some replacement caps from Digikey. Hopefully desoldering the board from the wires to take it off the organ should not be too difficult. Or I could probably snip the leads of the bad cap and solder in situ directly to the old leads. Time will tell. Feeling optimistic.

[human-potato_hybrid]

Aaaaannnndd.... it magically started working again. I was "poking around" a bit by attaching caps in parallel with the other caps while the board was still on the organ, so I figure the problem is probably a solder joint or trace that is like 1 micron away from failure.

So of course the only logical option is to stick the cabinetry back on and hope the noise doesn't shake it loose again ?

If it happens again I'll desolder the board off of the Oregon and take a proper look at it. Going to enjoy the vibrato for now tho.

https://youtu.be/-P0oxtiNisM