Dynacomp issues

[Milotic]

Hi ladies and gents.

I recently finished another project, the Dynacomp from Sabro designs.
All is good, except the pedal isnt working.  I'm getting a true bypass 3pdt signal, but nothing when the pedal is activated.

Readings:

IC:CA3080E
1 = 0v  5=4.13v
2=4v    6=5.43v
3=4v    7=9.56v
4=0v    8=0v

Q1:2N3904  Q2: 2N3904  Q3:2N3904   Q4:2N3904   Q5: 2N3904 
C= 9.56v            C= 8.28v            C=4.89v          C=8.28       C=9.56v
B= 3.46v             B=0v                 B=5.42v          B= 0           B=8.28v
E= 5.09v             E=0v                 E=4.8v            E=0            E=8.99v


D1:1N914  D2:1N914   D3:1N914
A=0v                  A=0v              A=0v
K=9.56v              K=0v              K=0v

there are alot of zeros so im not sure whats going on.  If i had an idea, it could be potential shorts.

[R.G.]

If you'll read "Debugging: what to do when it doesn't work", you'll notice that it's important to give us a link to the schematic so we can relate your part numbers to what the circuit actually does.

In this case, the only info I can glean from it is that the CA3080 (of which there is only one) is either broken or not placed correctly in the holes or not connected properly. You can never get the Iabc pin (pin 5) on an OTA more than a diode drop (for 3080) or two diode drops (for other OTAs) above the negative supply.

But I can only guess at what the other transistor numbers mean. That's a poor basis for debugging.

[Milotic]

ah forgot about that.

http://www.sabrodesign.com/wp-content/uploads/2010/04/MXR-DynaComp.gif

how would i test if the CA3080 is broken or not?  When i received it, it was in a plastic tube, didnt see any anti static material around it, so it could be a possibility. 

[PRR]

There is much wrong here. Too much for any single part failure. Yet spot-checking does not find any fault with the plan.

What transistors did you use? Can you verify the pinout is C-B-E top-down on the plan as shown? (Some parts do not have B in the middle.)

What is the actual voltage at the point shown here? Did you make all the cuts and jumpers?

[Milotic]

hey

I used a 2N3904 transistor, the data sheet said it is C-B-E top-down.
The voltage at the circled point is 0v and there are 26 cuts and 12 jumpers.


regards.

[PRR]

> The voltage at the circled point is 0v

Should be 3V. Look for mistakes near there.

[Milotic]

I've looked over it again and again, i cant see anything wrong.  The capacitor im using is a 1uF 63v electrolytic, could that be the problem?

[PRR]

The 63V is fine.

There's a short to ground at that point.

Check cap polarity. That plan marks the "+" side of the cap, but most caps mark the negative side, and sometimes that is not clear.

Examine (again) for solder-bridges between strip B and strip C1-9, also the cut at C9.

Unsolder and lift one end of C8; does that point go to 3V?

Same for R8.

[Milotic]

Okay i found it!  there was a break in the track at C8.  Now the voltage at said spot is about 3.01v.

New values.

IC CA3080E
1= 0v, 2= 3.96v, 3= 3.96v, 4 = 0v, 5 = 6.58v, 6 = 2.3v, 7 = 9.55v and 8 = 0v

Q1 2N3904(Q1-Q5)
C=9.55v, B = 1.35v, E= 1.62v

Q2
C=8.28v, B=0.01v, E = 0v

Q3
C=7.22v, B=2.5v, E=2.27v

Q4
C=8.28v, B&E = 0v

Q5
C= 9.55v, B = 8.28v, E = 8,98v.

D1 1N914
K=9.55v, A=0v

D2 1N914
K=0.01mV, A = 0v

D3
K=0v, A=0v.

This hasn't completely resolved the issue, but its another step closer.

Thanks.

[PRR]

> there was a break in the track at C8

Faults like that usually come in groups. And even though it is an eye-pain, detailed visual inspection finds most faults faster than tests and logic.

(in this plan) Q1, Q3, and Q5 should be "normal linear bias" which means their Base should be a few tenths higher than their Emitter.

So many of your numbers defy this, yet would make sense if E and B were confused.

> Q1 C=9.55v, B = 1.35v, E= 1.62v

Please verify that you are reading these points:

[Milotic]

I see what you mean.


This is the 2N3904 diagram i got from the data sheet.  So i just plugged it in like it is, with C at the top.
Here is a picture of my circuit.
http://www.flickr.com/photos/54529948@N07/5253260113/in/photostream/

The Q1, 3 and 5 readings, i doubled checked with your picture, and its about the same as what i've listed before.

[Milotic]

I tested the transistors with a multimeter, using the diode setting.  From that i determined that the central pin is the Base pin.  I understand that the Base needs to be more positive relative to the emitter, but its not for the case of Q1 and Q5.  Would this suggest a leakage or short somewhere or a faulty transistor?

I also tested the diodes, and I'm getting different readings from different ground locations.  the banded end had mV readings between 0-77mv, not sure if it is relevant or not.

[PRR]

> I'm getting different readings from different ground locations

All "grounds" should be "the same".

A mis-connected ground would explain why so many things don't "make sense".

You built a stripboard plan on perfboard. Go over the bottom and be sure ALL the strips are there, all joints good, all "cuts" open.

[Milotic]

I built this on a veroboard at first.

I've built it again using a perfboard, using tonepad's dynacomp pcb image.  I'm getting very similar voltage values still.
What am i missing?  Is there more than just soldering the components in the right place?

Image of Perf Dynacomp

http://www.flickr.com/photos/54529948@N07/5277470357/
http://www.flickr.com/photos/54529948@N07/5278080792/in/photostream/
http://www.flickr.com/photos/54529948@N07/5278080538/in/photostream/

Some of the tracks look like they are connected, but they aren't, i've checked using multimeter. 

[PRR]

What is all that grey stuff? Conductive ink?

Wire-scraps are more reliable.

Do not understand how two different builds could have different wrong voltages.

[Milotic]

The white stuff is a silver polymer. 
I think I'm going to give up for now, and just buy a pcb from tone pad.

Thanks

[Milotic]

Omg i just discovered i've been using 1N34 germanium diodes instead of 1N914.  they were mis-labeled, how embarrassing.
Would these incorrect diodes explained the poor readings?

[PRR]

No.