ross comp debugging

[bagudan]

Hi. I´ve been debuggung for 3 hours now. Built the ross comp from this vero layout

http://www.aronnelson.com/gallery/main.php/v/Toneys-Album/Rossv4.jpg.html

No sound coming through when the effect is engaged...usually one of the easy ones to fix? Ive checked componentvalues, orientation, etc... not getting anywhere. i´ll post my voltages here. Maybe someone can point me in the right direction?

q1 C=7,1v  B=2,1v  E =1,9v
q2 C=6,7v  B= 2,25v E = 2,2v
q3 C=8,6v  B=8mv    E =0v
q4 C = 8,3v B = 9mv  E =0v
q5 C = 9v  B=8,7v  E = 7,8v
IC 1=1mv , 2=20mv , 3=0 , 4=0 , 5=5mv , 6=2,75v , 7=9v , 8=0

Thanks in advance

[bagudan]

Been audioprobing through the signal path. I have audio as far as leg 2 of the IC ca3080E... but nothing coming out on the other side of it. I´m supposed to be able to hear audio from leg 5, right? Not that good with schematics. Maybe a dead IC?

[jgelderloos]

Leg 6 is the output for the CA3080. 5 is is the "Amplifier input bias" whatever that is. but i think the signal should be out of 6. im working on debugging the same pedal and im losing the signal at Q1..

[bagudan]

You´re right...got 5 and 6 confused there.....but still no signal from leg  6 though??

[R.G.]

q1 C=7,1v  B=2,1v  E =1,9v

Probably OK< but base at 2.1V and emitter at 1.9V isn't actually quite big enough. I think this is a measurement error.

q2 C=6,7v  B= 2,25v E = 2,2v

This is a problem. Check to see whether base and emitter are shorted together.

q3 C=8,6v  B=8mv    E =0v
q4 C = 8,3v B = 9mv  E =0v
q5 C = 9v  B=8,7v  E = 7,8v

Probably OK. Fix other stuff first then measure again.

IC 1=1mv , 2=20mv , 3=0 , 4=0 , 5=5mv , 6=2,75v , 7=9v , 8=0

Big problem.
Pins 2 and 3 are supposed to be pulled up into the power supply range a few volts. Nothing happens if they're sitting down at zero. Is the bias supply connected? Check the resistors which connect to these pins.
Pin 5 at 5mv means that it's not being pulled up to one diode drop by the emitter of Q5 and the sustain control. Is the wiring and soldering to the sustain control correct?

[rogeryu_ph]

Just wanna share....
I almost pulled out all the components and checked the parts and found out later the CA3080E i ordered was defective. To confirm this I made an audio probe and probe the pin6 has no output sound which also i verified this when i read somewhere not in this forum his built has the same Batch H0019 marked on the IC was giving him an headache. I email the on line store and immediately sent me a replacement. After swap in the new IC it comes alive!  This was the most difficult experience and lengthy hours i spent on a project, anyway i learned how to use the audio probe 
Hope this is not your case.

[bagudan]

Arrgh! Have tried everything....nothing seems to help. There is no short between B & E in q2, the sustain pot is wired as in the layout, Every resistor is checked and soldered properly in, caps orientation double checked..but still, no sound? I´ve ordered a new IC, and a 2k trimmer ( I used 2 1k resistors instead of the trimmer, read elsewhere on the forum that this would work?)
But if the IC is "broken", would this explain all the weird voltage readings?
-Kasper

[MikeH]

The likelyhood is not that you have a bad chip- it's more likely that you have a solderbridge, or cold joint, or an incorrect component in place.  Especially when working on vero; the opportunities for error are many and hard to avoid.

[bagudan]

Yeah I thought so;)
Guess I´ll be looking through the old magnifying glass again...these eyes have a hard time looking at copper stripes...

[bagudan]

Ok i´m back to debugging this thing. The two resistors connecting to pins 2 & 3 are 220k ( r 18 and 15 in layout) right? On one side of r 15 the voltage is 4,7 volts, but after this resistor it drops t 20 mv so no voltage reaches the trimmer? Have already changed this resistor. There is no short between base and emitter in q2, but i still get the weird voltage readings?

[bagudan]

Are pins 3 and 4 of the ic supposed to be connected... cause they are?
-Kasper

[R.G.]

Are pins 3 and 4 of the ic supposed to be connected... cause they are?

No, they're not supposed to be. Most likely problem is a pin-to-pin short, probably solder, possibly the traces that contact these pins at some distance from the chip.

Get out the magnifying glass.

[bagudan]

I found the short...somewhere else on the board:) Big vero´s are confusing to look at I think, difficult to compare to schematic... But at least I finally got compression, sustain, and volume....works like a charm. will have to check transistor voltages though, to see if there are other mistakes, but it sounds good though.

Thanks for all the help and patience

I´m trying to understand the switch that is supposed to alter the recovery time... to my ears it seems that there is a difference in when the sustain kicks in, so to say( Is that what it does, or is it not so simple).....only used to simple to-knob -comps here;)