UNI-VIBE UV1 no effect

tedsorvino · Post by **tedsorvino** » 29 Aug 2018, 17:20

Hello everyone.
I 've decided to give another real try to fix this pedal. It's the Rev A and the schematics I attach seem more or less the same.
I hope somebody is familiar with the design.

The pedal gives proper signal, but in any setting it's like there is no effect.
I 've made some initial tests with my DMM, signal generator and oscilloscope.

The sound comes normal out of the out. It can be amplified by the volume pot.
There is continuity to every pin of every pot with the main board. No problem with the ribbons. Continuity is also good on all the parts of the PCB i've tested so far. The PCB seems really new.
The two spst switches seem to work fine.
I power the circuit with 18V DC.

All voltages are correct ( A+ , B+, C+) all around the test points. Haven't tested all ICs yet.
The speed and the intensity pots are dead. The volume pot works properly. The pots seem perfectly normal and all connections are like brand new. As I said before....Continuity is perfect.

I tried to connect the expression pedal with a TRS jack and there is some movement on the oscilloscope screen on pin 2 of U12, according to the change on the intensity pot. There is no change on the output signal. There is no signal on most Us. Only on the TL 072 op amps.
There is perfect signal , but absolutely without any movement (modulation) around all Qs (even on all 4 LDRs) , up to Q17 - Q18. These two show the same symptoms like U12 (it seems normal to me, since they are driving the op amp). Without a TRS there is no movements whatsoever,

I suspect something with the TRS of the expression pedal out or something with the H11F3 opto, or something with the VR1 led cell. Maybe I'm wrong.

It seems difficult and it's more difficult since I haven't got a numbered layout with the parts values. The pcb is a mess. If you could help it would be fantastic.
Thanks in advance.

brejna · Post by **brejna** » 29 Aug 2018, 19:25

Did you check if lfo is working?

tedsorvino · Post by **tedsorvino** » 29 Aug 2018, 19:51

how can i do that? Open the small box in the middle? What am I looking for? The photo resistors seem to work. I don't know what i'm looking for around vr1.

brejna · Post by **brejna** » 29 Aug 2018, 19:56

Check if lamp is working under the mini metal box..

tedsorvino · Post by **tedsorvino** » 29 Aug 2018, 20:18

Yes it is. It takes some time to start...but when it does it follows the movement of the intensity and speed pots. Even if press the bypass button it doesn't switch off. I think it's ok....But effect wise...nothing really happens

ps . I realized that when I max the speed knob it stops. And then after 30 seconds it starts again. Is it because it's out of the box??

brejna · Post by **brejna** » 29 Aug 2018, 20:22

Then check if the effect is switched when engaged..

tedsorvino · Post by **tedsorvino** » 29 Aug 2018, 20:32

Is there a way to change the lamp. I mean...can you tell me what the exact spare part is. Because it seems unsable. When it's working everything works well, but when it doesn't, everything stops. I will try to resolder it , but I would like to change it if it's something simple. Is it the lamp or the photoresistors or vr1 (the lamp's driver)?
Why, when intensity and speed are at their max (especially the speed pot), does it stop?
has it got something to do with ground (the ring on top of the pot)?

DrNomis · Post by **DrNomis** » 30 Aug 2018, 02:51

Normally what should be happening is that the lamp should be varying in brightness at a slow rate with low settings of the speed control, as you turn up the speed control the lamp should vary in brightness faster, that's assuming that you've also turned up the intensity control as well, if the lamp is not varying in brightness, that could mean that the LFO is not oscillating as it should, or, the signal from the LFO is not getting to the lamp driver, first thing I would do is check to see if the two LFO transistors are still good, since the LFO will not work if they are blown, if they are good, check to see if you're getting a signal from it at the Intensity control pot, if not, then there's a possibility that the coupling caps could be no good.

I'm suspecting that either Q16, Q17, or Q18, or maybe all three of them might not be working correctly, so I would check to see if they are all good, and then check the 10uF coupling cap that connects to one lug of the intensity control, if those are all okay, then check the three 680nF caps in the LFO circuit, check the two back-to-back diodes as well, there should be roughly half the supply voltage on Q17's emitter, if not, that could indicate that Q17 and Q18 are faulty.

Hope that helps....

P.S. Did you set the lamp driver trimpot properly so that at minimum intensity settings, the lamp glows a dull-orange colour?

The lamp I used in my Univibe build (if my memory serves me right) is a 12V/60mA type.

tedsorvino · Post by **tedsorvino** » 30 Aug 2018, 08:56

Thank you DrNomis for the thorough response. I carried all tests as good as I could.
Now I realized somehow the extent of the problem...since all tests were successful but the problem persists.
It seems really hard.

Well all voltages seem fine. All 680n caps give good voltages and they feed Q18 base with about 6V and then both q18-q17 emmiters give about 7.5V variable DC.
Then Q 16 collector gets the same voltage and the emmiter gives something like 0.5V (normal since it goes to ground I think)
The 10uF seems good too, Same voltage there.
The lamp is set well.

Here are the symptoms.

When I max the volume and the intensity there is no problem on the lamp's movement. When I max the speed (after half way of the pot's distance) the lamp stops and needs some 30 seconds to restart with the speed pot backed.
The chorus (green light) responds well up to a certain speed level. Then the symptom appears.
The vibrato sounds way too weak and of course fast vibrato is out of question.
The complex of U5 - U6 seem to work ok. When there is voltage on one side there is no voltage on the other (when I press the switch and the led changes colour).
The overall level seems not so loud.With the volume maxed it 's not louder than the bypass signal.
With the pedal attached (and switched on) there is no real response.
Don't know what to do with the trimpots (what to expect) so I leave them alone. The lamp has a dull glow when it's idle or at minimum settings.

I guess it's not fed well on some sides of the board signal wise. Maybe some kind of short. Or really bad photoresistors or lamp. They are fed well voltage wise.

tedsorvino · Post by **tedsorvino** » 30 Aug 2018, 11:35

Update

After measuring signals at the output.

The volume cannot get above 3.5V of amplitude whatever signal I feed it. The effect (both chorus and vibrato) works with a speed of up to about 45%. After that it dies and starts after half a minute. The thing is that the pot is a reverse audio one. I don't know if that really matters.
With the pedal plugged and switched on there is no movement regardless of the pedal's movement. The signal is effected. With the pedal switched off, the signal is bypassed.

Thanks for your time.

DrNomis · Post by **DrNomis** » 30 Aug 2018, 12:50

tedsorvino wrote:Update

After measuring signals at the output.

The volume cannot get above 3.5V of amplitude whatever signal I feed it. The effect (both chorus and vibrato) works with a speed of up to about 45%. After that it dies and starts after half a minute. The thing is that the pot is a reverse audio one. I don't know if that really matters.
With the pedal plugged and switched on there is no movement regardless of the pedal's movement. The signal is effected. With the pedal switched off, the signal is bypassed.

Thanks for your time.

So if I'm reading that right, with the speed controller unplugged, the speed control on the Univibe changes the speed of the effect, when an external speed control is plugged in, it has no effect on the speed of the effect, that suggests to me that it could be an issue with the speed controller itself, I'm thinking that the reason why the effect dies when you increase the speed is probably due to a coupling cap taking too long to charge and discharge, or, there could be a leaky cap somewhere, note that I'm using my Univibe as a reference here, it's based on a design called the Forum Vibe, which uses discrete transistors (about 13 of them) in the circuitry, so it's circuitry is a bit different to your build, although the LFO and Lamp Driver circuitry is similar enough, what generally should happen is that at slow speed settings the lamp should be relatively dim and vary in brightness, as you increase the speed, the overall brightness should increase as the speed of the effect increases over the full range of the speed control pot, I built an external speed speed control pedal for my Univibe, using the plastic case of a non-working Proel Wah pedal, and a dual-gang 100k log pot wired in reverse so it worked normally with the mechanism of the plastic Proel Wah case, it plugs into the external speed control socket on my Univibe by a short cable that uses two stereo 6.5mm plugs, seems to work pretty well.

One thing I've noticed with my Univibe build, is that with a +15V DC supply, the signal level coming out of the effect can be as high as about 3V, as in the case of your build, before it starts to clip at the top, this is normal.

DrNomis · Post by **DrNomis** » 30 Aug 2018, 13:09

tedsorvino wrote:Is there a way to change the lamp. I mean...can you tell me what the exact spare part is. Because it seems unsable. When it's working everything works well, but when it doesn't, everything stops. I will try to resolder it , but I would like to change it if it's something simple. Is it the lamp or the photoresistors or vr1 (the lamp's driver)?
Why, when intensity and speed are at their max (especially the speed pot), does it stop?
has it got something to do with ground (the ring on top of the pot)?

If your lamp is soldered to the circuit board, then changing the lamp is as easy as desoldering it and then soldering the new one in place, I bought the lamp used in my Forum Vibe build from my local Jaycar Electronics store, it is a 12V/60mA grain-of-wheat type that mounts on the circuit board via two pigtails that poke out of it's glass envelope, the four LDRs used in my build are just some standard ones I bought from Jaycar Electronics, I think from memory they have a dark-resistance of 10M, the original Univibe's lamp was a 24V type, but no one seems to know the exact specs of the LDRs used since the manufacturer of the Univibe probably had them custom made.

If possible, do a quick internet search for the Forumvibe, you should be able to find a pdf that has a lot of info on the Univibe.

One thing you will notice is that the Univibe effect is a bit subtle at low speeds, but gets more prominent as the speed increases, this is normal and seems to be due to how the LFO behaves, as the LFO's speed increases the level of it's output signal seems to increase as well, the side-effect of this is to compensate for the Lamp's sensitivity to the current flowing through it, so it gets brighter.

tedsorvino · Post by **tedsorvino** » 30 Aug 2018, 13:12

The speed controller is pretty much similar to yours and works the same way. I doubt it that there is something wrong with the pedal but i will check it.
I don t doubt that it s a coupling cap? But which one? Where could I check?

DrNomis · Post by **DrNomis** » 30 Aug 2018, 13:23

tedsorvino wrote:The speed controller is pretty much similar to yours and works the same way. I doubt it that there is something wrong with the pedal but i will check it.
I don t doubt that it s a coupling cap? But which one? Where could I check?

It could be the 10uF cap on Q17's collector, or the 680nF cap on the wiper of the intensity control, but a bit unlikely if it's a greencap, the original Univibe used a 1uF cap where the 10uF cap is, and a second 1uF cap where the 680nF cap is.

This link to the Forum Vibe pdf should prove useful, copy it into your internet browser:

basicaudio.net/univibe-ForumVibe-final.pdf

tedsorvino · Post by **tedsorvino** » 30 Aug 2018, 14:43

I think it s more likely that it s an electrolytic. 680nf is tantalum. Highly unlikely that there may be a problem.

tedsorvino · Post by **tedsorvino** » 30 Aug 2018, 17:59

The cap on the wiper is 120nf and it's a film one (so it could be leaked). On first look the connections and the appearance on both caps looks brand new. The page you suggested is a really helpful one. Thanks a lot.

tedsorvino · Post by **tedsorvino** » 31 Aug 2018, 17:00

After thorough scoping around the intensity and speed control area of the schematics and proper measuring of the electrolytic cap out of the circuit I think it must be a problem around the Q12 - Q13 J fet transistors. Since I have a problem after a certain amount of speed control and the expression pedal doesn't work. That's the are where both operate.
I also realized that the expression works properly, since I can see correct movement from it on most parts of the quad transistor Q14 ( 3 - 4 and a part of 2), Q 15 and the lug of the opto isolator that corresponds to it.
So since Q14 - 1, Q 13 and Q12 don't work with the expression and Q 12 is connected to the speed pot, I will start with Q12 and Q13.
Q 14 is out of question that is faulty.
From the opto isolator and afterwords, there is movement without the pedal (with the pedal there is no movement on Q 16 - Q 17- Q 18 and U12).
The only other option is to have a faulty Q16 or 2,2 uF electrolytic. I will check it after changing the FETS.

tedsorvino · Post by **tedsorvino** » 10 Sep 2018, 18:45

Just an update. After some tests and changing the Q12 transistor, came to the conclusion that it's either the optocoupler or q17-q18 (maybe q16). The reason is that things go well up to the entrance (two legs) f the optocoupler. But they freeze at the exit (three legs). The two transistors are at the exits side and the third one is at the far side of it, next to the led (seriously doubt there is something with it) I ordered all of them.
If nothing comes out of these tests...I give up. Not worth it really.

lolbou · Post by **lolbou** » 12 Sep 2018, 12:50

I once repair one by simply resoldering the optocoupler (NSL39...). I took it off, it was fine, soldered it back in and voilà!

It was nearly a decade ago, but the unit still works fine AFAIK.

Did You try altering the values of TP1 and TP2 (noting their positions at first)?

The part of the circuit you're looking at is the one i really never get to understand. I hope my trace is correct, since i don't get the point of the bunch of FETs, BJTs and trimpots in that part...

tedsorvino · Post by **tedsorvino** » 18 Sep 2018, 20:28

ready. a combination of problems on opto, q17 and q18. replaced them. everything's good. took some time but we ve made it. thanks for the help guys. i do appreciate it.