Electrovibe - no slow speed (LFO stalls)

[Kester]

Hi,

I just finshed wiring up an Electrovibe, and there seems to be an issue with the speed controls:
When the speed is turned up full, or almost full, the bulb is turning on and off as it should. However, when I turn the speed control down the lamp stops pulsing and just stays on, although not quite as bright as the maximum brightness when the speed control is up. It does exactly the same thing for both speed controls.
Does anyone know what a likely cause of this could be?
Where would be a good place to start troubleshooting?

Thanks,
Kester

 

[Big Monk]

Post pi

Hi,

I just finshed wiring up an Electrovibe, and there seems to be an issue with the speed controls:
When the speed is turned up full, or almost full, the bulb is turning on and off as it should. However, when I turn the speed control down the lamp stops pulsing and just stays on, although not quite as bright as the maximum brightness when the speed control is up. It does exactly the same thing for both speed controls.
Does anyone know what a likely cause of this could be?
Where would be a good place to start troubleshooting?

Thanks,
Kester

Post pictures of the top and bottom of the board and double check the speed pots.

 

[Kester]

Hey, here are the photos of the top and bottom. I know the soldering isn't the tidiest, but it's the first time I've run into an issue when putting a pedal together, although this is only my 7th one... Also, the LDRs aren't properly positioned yet - I know I need to do some tweaking with them!

Hopefully you can spot something anyway!

 

[Kester]

Some more information:
If I power the pedal with either speed control set slow, the bulb pulses for a couple of seconds and then gradually stops (and just stays on as before).
Also, all audio aspects of the pedal seem to be working fine, so I'm guessing the problem is just with the LFO section.

Any advice would be greatly appreciated!

 

[fig]

It’s always good to make certain the transistors are making good contact on all pins when using SIL-sockets, and there are 45 of those pins in this circuit.

 

[Big Monk]

Also, is this happening with both speed controls?

 

[Kester]

It’s always good to make certain the transistors are making good contact on all pins when using SIL-sockets, and there are 45 of those pins in this circuit.

They all seem solid enough. I've tried a couple of different transistors in all the positions too, but they don't make any difference. One of the cables for my multimeter isn't working but I'm going to sort that out after work and try some measurements.

 

[Kester]

Also, is this happening with both speed controls?

Yes, exactly the same with both speed controls.

 

[Kester]

I haven't been able to get any readings yet, but here's the progress so far:
- I swapped the 2n5088 transistors in the LFO circuit and bulb driver circuit for 2n3094 transistors. I didn't think it made any difference at first but I'm now able to reduce the speed slightly on both speed controls before the lamp stalls.
- I've swapped out the capacitors in the LFO circuit.
- I did the high speed increase mod - just for one pot, in the hope of getting 2 slightly different speeds at least...
- I swapped the low speed resistor in case that was defective.
- I reflowed all the solder points (including switches and header pins).

So just to clarify the current situation:
-The audio side of the pedal works fine - it sounds like a univibe and isn't noisy or anything.
- Both speed controls work in the upper 20% of travel (fast and slightly slower). However, if I turn them down any more than that, the LFO stalls and the bulb just stays on.

I feel like there must be a very obvious solution, but I just don't know what it is!

Has anyone spotted any potential issues in the circuit board pictures?
Any suggestions on any specific LFO circuit components that might be causing this to happen?

 

[Big Monk]

Did you reflow your Speed pot joints?

 

[Kester]

Yes, I reflowed them too.

 

[Kester]

Hey, I took some measurements of the voltages in the LFO section. Obviously some of them vary, so these are just the maximum figures:

Speed control on the slowest setting:

Q1
b: 2.22v c: 17.39v e: 6.66v

Q2
b: 6.54v c: 17.39v e: 5.92v

Speed control on the fastest setting:

Q1
b: 2.22v c: 17.46v e: 6.82v

Q2
b: 6.82v c: 17.46v e: 6.24v

I get a reading of 12.15v at the the input of R11, and 7.13v at the input of R12. The output from R12 is 2.22v (the same as the base for Q1).
The rest of the reistors and diodes in the LFO circuit all read a maximum of 6.19v.

Can anyone see anything obviously wrong with these readings?
Let me know if any other measurements would be necessary!

 

[Big Monk]

Does this occur at any intensity level?

More directly: When the lamp goes full on at slow speed, how does by The intensity control affect your issue?

I’m wondering if you are shorting out the LFO section somehow.

Does this issue occur with the effect outside the enclosure as well?

 

[Kester]

The intensity control works as it should on the fastest settings, but doesn't have any effect on the brightness of the lamp on the slow settings.

 

[Big Monk]

The intensity control works as it should on the fastest settings, but doesn't have any effect on the brightness of the lamp on the slow settings.

Retrace your steps and focus here:



There shouldn't be a scenario in normal operation where the lamp goes full-on. It's as if you have something acting as a cancel switch in the LFO circuit.

 

[Kester]

Does this occur at any intensity level?

More directly: When the lamp goes full on at slow speed, how does by The intensity control affect your issue?

I’m wondering if you are shorting out the LFO section somehow.

Does this issue occur with the effect outside the enclosure as well?

It seems to be the same whether it's in or outside the enclosure.
I've gone over the traces and points with a magnifying glass to look for possible shorts, but haven't found anything... well, nothing above the surface anyway .

Do the voltages seem ok?
I've read that the LFO circuit not receiving enough power can be a common univibe problem

 

[Kester]

Retrace your steps and focus here:

View attachment 27227

There shouldn't be a scenario in normal operation where the lamp goes full-on. It's as if you have something acting as a cancel switch in the LFO circuit.

I think it goes to medium intensity when the speed control is turned down, It's definitely not as bright as when it's flashing on the fast setting.
But yeah, it's like something is just turning the LFO off when it goes below a certain speed.

Do you think I should start swapping components out?

 

[Big Monk]

It seems to be the same whether it's in or outside the enclosure.
I've gone over the traces and points with a magnifying glass to look for possible shorts, but haven't found anything... well, nothing above the surface anyway .

Do the voltages seem ok?
I've read that the LFO circuit not receiving enough power can be a common univibe problem

Your issue suggests some sort of installation or workmanship error.

Like I said, there shouldn't be a scenario in "normal" operation where the bulb goes full on. If anything, the only time it should get anywhere near full on is if you have the trimmers set to high brightness and you are on a FAST speed, not slow speed like you are seeing. On slow speeds, the bulb should be pulsing very slowly.

Go through the LFO section and Lamp section and inspect all your work. Also inspect the Intensity and speed pots.

 

[zgrav]

are you powering more than the univibe on your power supply when testing it? it can be a bit of a power hog.

 

[Kester]

are you powering more than the univibe on your power supply when testing it? it can be a bit of a power hog.

I’ve just been using a Mooer wall-wart adaptor at the moment, but with no other pedals connected… I don’t use many pedals live and they generally run on batteries anyway. Although I also finished a Hydra delay pedal a couple of weeks ago so I think I may need to invest in a decent power supply!

The Electrovibe should still work fine by itself from a regular 9v adaptor for now though, right?