Repair Advice Univibe Clone

[Noob BOB]

Ok so... firstly I guess I should say hello to everyone.
Here it is, I have a univibe clone with these symtoms/illness. I guess I am what you would call a dangerous DIY repair tech in the sense I have minimal knowledge of electronics yet enough to be able to repair some of my own gear and stuff for my friends. I have the balls and the confidence to pull anything electronic apart to see if I can find any obvious signs of damage or failed components. I have fixed a few vintage tube amps in my time fenders, Marshalls, Traynors.
So for anyone who is reading this post my thanks in advance to you and for any input/ insights etc... any steps toward a solution is greatly appreciated. I do know may way around electronics and components and how they work for the most part.
But when it comes to a univibe circuit I have not tried to attempt a repair nor have I ever looked inside to see what makes them tick.
After reading and poking around on the internet and being confident enough to open up this pedal I have come to this conclusion.

(my trouble shooting skills are very limited).

Anyhow the patient is a FULLTONE DEJA-VIBE CS-MDV MK2 A beautiful repop clone of the shin-e-vibe sound. However the components in this particular model are so small and some are surface mounted (soldered without holes in the tracers) to the PCB and my eyes just dont work like they used to. LOL
So here is what I have found so far with my primitive trouble shooting.
I power up the vibe. It oscillates with a lush pulse for maybe 2 secs perhaps 4. Then the indicator led dims and loses the pulse intensity. After opening up the pedal and a bit of poking around I could not visibly see any damage. I have removed the metal shield that covers the LDRs and the bulb although very dim the bulb is infact still flashing/pulsing. But very dim. I have since turned the trim pot to increase /decrease current to the bulb it does infact get even dimmer than it was as the trimmer was already maxed out from the factory. So I ruled out this part of the circuit being the culprit. What I did notice after removing the sheild surounding th bulb and LDRs then powering the unit off then on again, upon the initial power up (applying 18v 100mA) the bulb infact is almost 3 or 4 times brighter from initial power up but within seconds it becomes dim and a dull pulse. Very anemic. Although still flashing and offering little to none of the desired warble effect. Even with all dials pots maxed out for intensity and volume. However when I max out the speed pot the warble does get more pronounced. So with all dial maxed out on the unit i then powered down the unit and powered up again. The same symtoms occur. Very bright bulb initially gets dim almost immediately. I then decided to do one more test. To be absolutely sure I have narrowed the problem down one step further I decided to take an external light source (A brighter than the bulb flashing LED) and used it in close proximity to the LDRs to infact determine without a doubt that they themselves were functioning as they should.
Although the LED did not give the same throb effect as you would expect to get from a univibe due to the harshness and abruptness of the flash as it is not gradual, it did however increase the intensity of the warble substantially. So at this point I have deduced that the only problem is the light intensity the bulb delivers to the LDRs. I dont think the bulb itself is the culprit because initial power up it is 3 -4 times as bright before it tapers off to becoming dim.
So this is where I am at I will send photos. As I said before the components are small surface mounted and I cant read values or find schematics for this model. I have also contacted manufacturer for info and have yet to receive any reply.
So
My question is would it be a safe bet without trying to use a multimeter to measure tiny little transistor leads for voltage and possibly shorting them out or something else in the process. Is it a safe bet to assume the problem I am having lies in the transisotors?
Any other experienced advice and or input would be greatly appreciated.
I am honestly a bit intimidated by this particular pedal because the components are so flipping small I cant read values. Not to  mention I dont even think I have proper tools to remove and replace components of this size. I am limited to a standard iron however it is digitally temperature controlled so I can reduce the iron temp and keep it constant.
Please some advice from the gurus
Thank you kindly.
Oh one other thing after leaving the pedal on for an extended period of time the light fades to almost nothing and doesnt appear to flash no matter what the knobs are set to, then if I try to power it down and back on again the light doesnt have that initial brightness it did before. However if I wait a while before attempting the power the unit back up the light is indeed brighter initially then gets dim.
The longer it runs the dimmer and more anemic it gets.

[PRR]

> hello to everyone.
> my eyes just dont work like they used to.
> upon the initial power up (applying 18v 100mA) the bulb infact is almost 3 or 4 times brighter from initial power up but within seconds it becomes dim and a dull pulse.

Welcome!

Get light and lenses! From age 30 to 60 your eyes stiffen-up, won't focus close. That's why grandpaw has reading glasses. Find the $2 reader specs display in the dollar store, get 2.5X and 3.5X (4X if you can). Also get two of what we used to call "100 Watt" desk-lamps for your workbench. (I had four 37W fluorescent tubes, plus skylights, and old 3.5X readers on 1.5X myopia.)

If that is not working, get an eye exam. My vision was stable for decades and then it got worse. The spectacle guy saw the problem right away, not his job, but he got me to the right guy. Seeing better than ever.

When a thingie starts OK, and then sags, watch the supply voltage. It may say 18v 100mA but be bogus. I've had car batteries set at good 12.6V idle, then sag below 8V when trying to crank. Those little wallwarts have various on-load faults.

[Noob BOB]

Thanks for the advice however this is not a tired car battery.
Lol
And well the power supply is not the issue it was purchased new e weeks ago. Also I tested supply with meter and it is good. As well as used multiple different 18 volt guitar pedals and they function perfectly o  both of my 18v 100mA isolated outputs.

This is however a problem somewhere in the circuit which supplies the flashing bulb with volatge/current. It need the aswell/pulse variation to produce the "univibe effect".
I was really hoping to hear from someone who has had experience with any sort of univibe troubles/repairs and or suggestions as to where to start (eg Darlington  transistors) how to properly diagnose them, what to look for, be aware of etc..
Thank you for the quick reply
FYI I have dollar store glasses they work but the markings on the components are tiny and faded aswell
Again anyone who has experience with failing univibe pedals or repairs I would greatly appreciate your inputs advice knowledge  and experience.
It doesnt appear to me that mr. Fuller of fulltone is going to respond to my inquiry on schematics and part listings as he closed the door of his business as of the end of september 2022
Thank you

[GibsonGM]

[Eb7+9]

hoping to hear from someone who has had experience with any sort of univibe troubles/repairs and or suggestions as to where to start

Thank you

The LFO and bulb driver are the main source
of trouble in both clones and stock units

hope you have access to a scope
otherwise, lots of tail chasing

You need to see what your LFO is doing on its own first
ie., against speed pot, and then go east from there ...

—-

ps. lookup my bulb driver offset mod while you're at it

http://www.lynx.net/~jc/pedalsUnivibe.html

best ...

[Lino22]

When you plug the DC in, there is an opening burst of light, that is normal. It however takes more like 1/2 a sec than the 2 sec you mention, then the LFO settles down. But this wouldn't bother me.

I may have misread your post but i can't say what was the reason you got the pedal for repair.
In short - what is wrong with the sound or functionality?

[Noob BOB]

Sorry for the delayed response.
The pedal itself doesnt do the "vibe" thing very long.
As I said previously at power up the bulb flashes as it should I get chorus vibe thick and pronounced at first it immediately diminishes substantially in a few secs. In tandem with the bulbs brightness. After a short period of time it eventually stops flashing at all.
Sometimes I can get it started again by increasing the speed pot to maximum. (Bulb flashes strong but still quite dim. With a very non existen effect.little to no chorus warble univibe effect. And it will eventually die off again.
I can kick start it again upon power up. But the pattern repeats only quicker and more severe.
However everytime power is removed and reapplied it will start giving the desired effect and quit almost immediately. I might hear one full warble then it dies and I  tandem with the bulb and the indicator led. To the point where the light stays very dim almost off and wih no pulse in brightness. Again sometimes it can be kickstarted by maxing out the speed pot. I have also noticed it runs a bit better at max speed but no where near the proper sound of the chorus effect. It is weak tired basically non existent
Thanks again foe the replies

[Noob BOB]

hoping to hear from someone who has had experience with any sort of univibe troubles/repairs and or suggestions as to where to start

Thank you

The LFO and bulb driver are the main source
of trouble in both clones and stock units

hope you have access to a scope
otherwise, lots of tail chasing

You need to see what your LFO is doing on its own first
ie., against speed pot, and then go east from there ...

—-

ps. lookup my bulb driver offset mod while you're at it

http://www.lynx.net/~jc/pedalsUnivibe.html

best ...

Thank you for your help.
I dont have a scope, however I may have access to one . I have a friend with one I can probably use.
Again thank you for your insights I will definitely read the link you posted
I will do a bit more poking about and report back my findings

[Noob BOB]

 Eb7+9
ps. lookup my bulb driver offset mod while you're at it

http://www.lynx.net/~jc/pedalsUnivibe.html

[/quote]
Nice sounding vibe I know where I am.going if this one cant be repaired. Lol

[duck_arse]

is there a circuit diagram for this model? does this model use a dual-gang pot for the oscillator rate setting? what are those two vactrols near the rate pot for? leading questions? sure, why not?

it sounds like a classic phase shift oscillator dying from a wrong value in the feedback/shift string. if that unit uses a single pot to control a pair of vactrols in the legs of a phase shift osc, I'd be testing the operation of the leds, the ldrs, and the legs to ground goodness. and the frequency pot.

[Noob BOB]

I am still waiting on a reply from mike fuller of fulltone regarding a circuit diagram.
(At this point i am not holding my breath)
If there is one out there somewhere I cant find one.
NO dual gang pots.
I have tested LDRs with a external light source (flashing led from my head lamp) and the circuit works as expected with the external light. I suspect a transistor or something in that path that provides power or regulates power to the bulb failed or is failing. As the bulb itself works and flashes but it's very dim almost off.
Cant read any part numbers on the transistors they are faded and too small.
I have not had anytime to do anymore diagnostics. Life duties blah blah...
I do have access to scope tomorrow so I will check things out more then.

There are 3 trimmer pots inside, one corresponds to speed, one is the bulb intensity brightness ( both appear to do what there are supposed to) however the trimmer pot for bulb brightness is set to max and although it gets dimmer when I turn it down at max setting it's too dim to trigger the LDRs to make any substantial difference in the operation sound. Except as I noted previous, during the initial power on the bulb shines nice and bright at first then dims quickly thereafter.
The vactrols I am uncertain as I have not traced thier leads through the entire path. But  they are connected to the speed pot and the indicator led on the front of panel which flashes in tandem with the speed of the LFO bulb. Both controller by the speed pot on front panel.
As I said I am going to put it on a scope tomorrow at a friends house and see what it can tell me.
It would be nice to see a schematic or at very least someone with the same pedal with values and part numbers you can read on the components.
This is not a cheap clone it's supposed to be
"one of the best"
They sound great!!! When they work

[Eb7+9]

I am still waiting on a reply from mike fuller of fulltone regarding a circuit diagram.
(At this point i am not holding my breath)
NO dual gang pots.

This is not a cheap clone it's supposed to be
"one of the best"
They sound great!!! When they work

Mike replaced the LFO dual pot by a pair of opto-couplers and just like in the case of a dual-pot both sides need to be fairly matched in the travel

Ideally you want the pair to go from around 1k to 100k ohms

To make a measurement snip one leg of each Rcell (half-way for easy bridging afterwards) to decouple from rest of LFO

... following this you need to reverse the circuit so we/you know what's what

[Lino22]

Just for my couriosity - the problem is clearly somewhere in the LFO. Why would he measure LDRs? They are not a part of the LFO, they most definitely don't cause the LFO go weak after a while.

[duck_arse]

Mike replaced the LFO dual pot by a pair of opto-couplers and just like in the case of a dual-pot both sides need to be fairly matched in the travel

matched? why? the speed pot isn't calibrated, is it? it's only a PSO after all, it's harder to get them to not work than it is to get them running with odd values all through.



Lino22 - the phase shift osc usually has two resistor legs to [AC] ground in the phase shifting network. these can be a fixed and a variable, or dualgang variable. if you have instead a single pot controlling the current fed to the leds in a pair of vactrols, the ldrs in those vactrols can then be the resistors in the R//C legs of the phase shift.

it is easy enough to get a PSO to work across the full range of a single gang 100k pot with a fixed other leg, and with the clipping diodes included you get a very even level of output. many hours stuffing about with pso's and odd values of caps learns you good how the oscillator will start strong, but then die from dampings over time. so you swap a cap or a stop resistor, start it up again, watch the squiggle on the cro ......

[Eb7+9]

Just for my couriosity - the problem is clearly somewhere in the LFO. Why would he measure LDRs? They are not a part of the LFO, they most definitely don't cause the LFO go weak after a while.

The LDR's inside the two opto-couplers that set the LFO speed ...

[PRR]

is there a circuit diagram for this model?....

+1

...The LDR's inside the two opto-couplers that set the LFO speed ...

I don't think the LDRs set LFO speed? If we had A SCHEMATIC to reference, we might have less wheel-spin.
http://www.pisotones.com/Univibe/Stratotrasto/FOTO3.jpg

[puretube]

is there a circuit diagram for this model?....

+1

...The LDR's inside the two opto-couplers that set the LFO speed ...

I don't think the LDRs set LFO speed? If we had A SCHEMATIC to reference, we might have less wheel-spin.
http://www.pisotones.com/Univibe/Stratotrasto/FOTO3.jpg

Eb7+9 is very probably right - we see a single pot in the lower left corner & 2 vactrols located to the north of it , here:
https://postimg.cc/w1yGk2F7

[Noob BOB]

Ok so I spent a little time with a scope this evening and I followed the signal through the circuit as best I could.
( my knowledge is very basic)
(I can fix old single channel handwired tube amps )
This is new territory for me surface mounted microscopic lol
Anyways I found signal on all transistors both emitter and collectors some were amplified signal some appeared same size as generated signal. All had signal except one. Which was located in the pair to the right of the speed pot. South of the vactrols.
the vactrols both have from what I could see on the scope fairly equal signal on the same side resistor legs. All the pots function as they should (eg vol pot increase amplitude etc..) even the trimmer pots.
I was able to read a few of the transistor part numbers with a powerful magnifying glass they are all the same part.
3EM one transistor was 7AW.
The one which I had no signal wave was a 3EM. However there is multiple settings (modern vintage switch and vibe chorus switch) on the pedal so I tried to check all of them but it was getting late so I cant say for sure if that transistor was bad. Nor have I used a multimeter to properly check them. So I feel as I am getting closer to an answer.
I also want to thank everyone for their input as I am picking up knowledge from your debates lol
Last note
*** even if I manage to pinpoint the problem WITH all of your help of course. I am not even sure I will be able to install new components.***
For example if i have to install surface mounted transistor or remove anything. It is going to be a chore just to get it out without melting something else in the process.
Anyways not much more to report.
I'm sure one of you if not all of you would have found the issue long ago.
Still no sign of a schematic, if I had something to reference I could atleast find my way through more easily.
Still no reply from manufacturer. (This is still under warranty  too) 2018 produce date 5 year warranty.
Whatever.

[Eb7+9]

Still no reply from manufacturer. (This is still under warranty  too) 2018 produce date 5 year warranty.

Mike doesn't owe you a schematic ... you'll have to DIY your own
No point discussing this further without going the distance...

[duck_arse]

it strikes me that you could test the ldrs, at least, by getting two resistors - value not important - between 10k and 33k, say, they don't even need to be the same value. tack them across the vactrols as shown, solder, clips, hand-held, set the osc rate to slowest, power on and observe the lamp behaviour.