Problems with guitar pedal Ibanez PC10

[eduardo_gj1]

Hello, I am trying to repair a guitar pedal, which already works almost everything perfectly at the exception of the flanger potentiometer, I already check the potentiometer and it works correctly, now when I put the potentiometer to full, only oscillation is heard, they could indicate me What could be causing this problem?

i attach the Schematic

thanks all for your help

 

[rjenkinsgb]

If it's not working at all, I'd start by checking SR4, then the caps C6, C25, C26?
If the audio input and output stages are working OK, there is not much else in that signal path.

If you mean it's oscillating, then try turning down the level on SR4 until it's just stable with the pot at maximum?

 

[eduardo_gj1]

I check SR4, then the caps C6, C25, C26 and everything its ok, then i turn down SR4 and its the same, it's not oscillating but the flanger pot doesn't work

 

[alec_t]

Your link in post #1 is broken, as the file is on your pc.

when I put the potentiometer to full, only oscillation is heard

That suggests to me that the pot resistance track could be damaged at the 'full' end (pin 3), or the wiper connection to the track there is poor. If the wiper is effectively open circuit it may pick up interference or result in circuit instability. I'd try temporarily shorting pin 2 of the pot to pin 3 to see if that stops the oscillation.

 

[eduardo_gj1]

I don't know, the link is fine for me. and the oscillation stops after lowering the SR4 now, I think it could be the flanger potentiometer and I noticed that the speed potentiometer (VR5) also has the same behavior, only that the speed works normally only when it is full, so I think I'll have to change both potentiometers and check if they work again.

 

[alec_t]

I don't know, the link is fine for me.

For you yes (because the file is on your computer), but not for others.

 

[rjenkinsgb]

For you yes (because the file is on your computer), but not for others.

It's worked fine for me, since I first saw the question - it opens a .pdf of the schematic.

 

[eduardo_gj1]

I attach the file again, but it is normal. I opened the .pdf in 2 different PCs and it opened well, but, for now, I don't think the pots are damaged, I'm not sure it's the problem, can I check another component or something?

 

[alec_t]

Ok. Pdf downloaded. Thanks.

 

[eduardo_gj1]

great, if you can help me too, will be really helpful, i really dont know where i can check i already check all the ic, and they are all goods but, i dont know if the capacitor are good the mesure on the caps it ok but i dont have a ESR multimeter

 

[alec_t]

Are all the voltages on pins 16, 17, 18 of the unit correct?

 

[eduardo_gj1]

Are all the voltages on pins 16, 17, 18 of the unit correct?

yes its a little low but its not so much

17=4.903v

18=2.448v

16=8.80v

 

[rjenkinsgb]

Do the chorus effects work as they should on both channels??

 

[eduardo_gj1]

Do the chorus effects work as they should on both channels??

yes, in both channels work fine, the problem its in channel B the speed and the flanger pot doesn't work as well, the speed pot in channel B only work when its full and the flange not work at all, or when its full the flange pot its oscilate but not now after i down the SR4 trim pot

 

[rjenkinsgb]

The speeds from the two oscillators look to be vastly different; one use a 0.056uF timing cap, the other around 22uF.

Is the slow one supposed to give a much lower range, so it's just not obvious when tuned down?

If your multimeter can read frequency, see what you get on pin 7 of IC8 and IC9, over the full range of each speed control.

With the "width" controls at maximum, also check you get the same frequency and DC voltage on pin one of IC3, depending which channel is selected.

If not, see what the DC level is with the working channel and try adjusting the bias (SR1 or SR2) for the bad one to the same level on pin 1, if it's not that already.

 

[eduardo_gj1]

pin7 on IC8 =11,40 and 15,20hz

pin7 on IC9 fluctuates too much, it is between 5.6hz 14.04hz, 16.80hz, 11.24hz

voltage IC3 pin 1 channel A = 1.9volt

voltage IC3 pin 1 channel B = 3volt 29and frequency 33.52hz and 18hz

 

[rjenkinsgb]

OK, as chanel A (using IC9) is working OK, try adjusting "SR2" while it's on channel B, to get a reading around 1.9V on IC3 pin 1.

 

[eduardo_gj1]

I tried, but the minimum I can adjust is 2.3v

 

[eduardo_gj1]

I cannot lower the voltage with the SR2 on channel B, the trimpot reached the maximum

 

[rjenkinsgb]

OK..

Do you have an oscilloscope?