Dynacomp full debug

[Dimitree]

Hi guys, I had a '78 dynacomp and I built one around that, so I redraw pcb and so on..
the problem is that this one is mute, no sound.
this is the debug:

1.What does it do, not do, and sound like?
2.Name of the circuit
3.Source of the circuit (URL of schematic or project)
4.Any modifications to the circuit? Y or N
5.Any parts substitutions? If yes, list them.
6.Positive ground to negative ground conversion? Y or N

1.Bypass is ok, when engaged it is mute, whatever position of the pots. *
2.Dynacomp
3.I built this from my original pedal. BTW the schematic is the same as the one by R.G. on geofex, but without the additional parts. *
4.No. even the bypass scheme is the same. I just added a DC jack connected just like the battery used to be connected (red to circuit, black to input jack)
5.no
6.no

* further info:
- when using a probe, the signal stops just after the CA3080 output, pin 6. I tried another chip I had, same problem, no sound there.
- I used 2SC1849, I tried one for Q1 before using them, it sounded (with a probe on the Emitter) with same pinout of 2N3904.


Measurements:

Voltage on the power supply = 9.24V
Voltage at the circuit board + = 9.24V
Voltage at the circuit board - = 0V


Q1
C = 9.24
B = 1.24
E = 1.45


Q2
C = 7.04
B = 2.37
E = 2.15


Q3
C = 8.1
B = 0
E = 0


Q4
C = 8.1
B = 0
E = 0


Q5
C = 9.24
B = 8.1
E = 8.75


IC (CA3080E)
1 = N.c.
2 = 3.92
3 = 3.92
4 = 0
5 = 0
6 = 2.37
7 = 9.24
8 = N.c.

photos:






I hope someone could help me to find the error
many thanks
Dimitri

[jacobyjd]

looks like the IC isn't in the socket

[caspercody]

Have you used a DMM to make sure none of your traces are shorting? Hard to see in the picture, but some by the IC look close?

[Dimitree]

looks like the IC isn't in the socket

just in the pic. As I said, I tried 2 different CA3080 I have.

Have you used a DMM to make sure none of your traces are shorting? Hard to see in the picture, but some by the IC look close?

no shorts "unfortunately", I tested each pin with each other  

[R.G.]

I used 2SC1849, I tried one for Q1 before using them, it sounded (with a probe on the Emitter) with same pinout of 2N3904.

+10 Goodie Points for checking the pinout!! 

Q1
C = 9.24
B = 1.24
E = 1.45

Either your meter is loading down the base of the transistor, or this one is having problems. Try again, putting the red probe on the base and the black probe on the emitter. This should read 0.5 to 0.7Vdc. If it reads 0.2V, there is a problem here.

Q2
C = 7.04
B = 2.37
E = 2.15

Same comments as for Q1

Q5
C = 9.24
B = 8.1
E = 8.75

Looks like the emitter is open. Check the path from emitter to the sustain pot by using your meter to read ohms from emitter to the pot itself. This should be less than 10 ohms (actually zero, but meters get funny down at low ohms).

IC (CA3080E)
1 = N.c.
2 = 3.92
3 = 3.92
4 = 0
5 = 0
6 = 2.37
7 = 9.24
8 = N.c.

Following up on the note above, Pin 5 is where the current telling the chip how much to amplify comes in. This pin is **always** at 0.4V to 0.7V on a 3080 if it's working. 0V on this pin indicates it is being TOLD not to amplify. This is what would happen if the wiring through the 27K resistor and sustain pot to the emitter of Q5 is open.

[jkokura]

Edit* RG is better than me. He gave you help, I just was going to say your trannie and IC numbers don't look right. He gave a solution, I didn't have one.

What he said.

Jacob

[Dimitree]

ok I tested: red probe on B and black on E, both Q1 and Q2 is perfectly 0.6V

about Q5 and the pot, the emitter is connected with the pot (it reads 0.2ohm), and indeed, if I measure the resistance between the emitter and the 27k resistor, it is 510k when pot at min and 0k when pot at max

pin 5 is still at 0V

really thanks to everyone, I really appreciate the help 

[R.G.]

ok I tested: red probe on B and black on E, both Q1 and Q2 is perfectly 0.6V

Those are fine, then. The meter was loading down the bias resistor.

about Q5 and the pot, the emitter is connected with the pot (it reads 0.2ohm), and indeed, if I measure the resistance between the emitter and the 27k resistor, it is 510k when pot at min and 0k when pot at max

Hmm. I would then use the meter to test for 27K to 537K from emitter of resistor to pin 5, since pin 5 is where it counts. If that works...

pin 5 is still at 0V

Then pin 5 is shorted to ground, either outside the chip or ... inside the chip...    These ICs (3080) are completely intolerant of currents more than 1ma into pin 5. They simply die, almost instantly, if that happens.

If you had a flaw that was pushing too much current in, it would kill every chip you put into the socket.

I hope that wasn't it.

[Dimitree]

so I found the problem    stupid me, I inverted the cable from the 27k with the cable to the output pot..so the 27k was going to output 
luckly you helped me to look around the 27k resistor
many thanks!
now the pedal works perfect (it seems) and the voltages are almost identical to my ex original dynacomp (I found the voltages on a sheet, I wrote them before selling it). The chip was working luckly.
BTW, I want to add, I have 2 sets of 1849 transistors, and those have different pinouts: a set is CBE and the other BCE, so please don't trust on what I've written before about the pinout and always test them before making the pcb 

[Greenmachine]

Hi,

I've got a dynacomp with some issues too.  If anyone can help, that'd be great.

There's a clicking coming from the output.  When the sensitivity knob is all the way up, the clicking stops, as does the fluctuation of the transistors.

I'm using 2n3904's.  

Voltages on CA3080 are as they should be (according to above in the thread), but there's a clicking coming from the circuit and the transistors affected are:

Q3:

E bouncing from 5.7-6.2
B same as E
C 9.66

Q4:

E 0
B bouncing from 0.0-0.02
C bouncing from 5.0-6.0

Q5:

Identical to Q4

Other Readings:

Q1

E 3.94
B 4.55
C 9.66

Q2

E 2.18
B 2.77
C 7.49

CA3080

1 0
2 4.8
3 4.8
4 0
5 0.62
6 2.76
7  9.65
8 0

Thanks for your help.

[PRR]

> Q5: Identical to Q4

Per the debugging thread:
Source of the circuit (URL of schematic or project)

The plan which I am looking at (1999 R.G Keen), it would make sense if Q3 and Q4 gave the same values, NOT Q4 and Q5.

Also Q1 B should be a bit lower than IC1 p6; you show very significantly higher. That could be correct for anOTHER version, but what version?

> There's a clicking

Per the debugging thread:
What does it do, not do, and sound like?
Does it pass signal?

Without specific insight, I'll suggest something is not connected.

[Greenmachine]

Thanks PRR.

Link to schematic (I don't seem able to add an attachment):

http://....org/viewtopic.php?f=1&t=10580&p=115820#p114674

It passes signal, compresses signal; however, there is a ticking present as well.  When the sensitivity knob is completely open, the ticking stops.

Pictures: http://www.freestompboxes.org/viewtopic.php?f=10&t=11431

[PRR]

"This" forum censors links to "that" forum.

Steve Mavronis' re-draw.

http://home.comcast.net/~snmavronis/mxr77dynacomp930x624.jpg

Your Q1 voltages are just wrong. Check connections, resistor values, and especially transistor pinout.

[mattthegamer463]

Sorry to resurrect but I figured that it would be better to post here than clutter up the forum with another Dynacomp thread.  I used the Tonepad layout and BOM, following their list for the Dynacomp (opposed to the Ross) if that matters.

Signal appears at the inputs of the CA3080 but not on pin 6.  Voltages are below.

U1
Pin 2 - 4.64V
Pin 3 - 4.65V
Pin 4 - 0V
Pin 5 - 0.604V
Pin 6 - 2.69V
Pin 7 - 9.19V

Q1
E 1.5V
B 1.9V
C 9.1V

Q2
E 2.1V
B 2.7V
C 7.0V

Q3
E 0V
B 0V
C 9.1V

Q4
E 0V
B 0V
C 9V

Q5
E 9.1V
B 9.1V
C 8.5V


There seems to be something affecting Q3 Q4 and Q5.  There is no voltage drop after the 150k resistor which is directly connected to Q5 base and Q3 and Q4 collectors.  Sounds like the culprit, but the value is correct, I don't know why there is no drop through it.  I'm out of ideas, does anyone have a suggestion?

[R.G.]

There seems to be something affecting Q3 Q4 and Q5.  There is no voltage drop after the 150k resistor which is directly connected to Q5 base and Q3 and Q4 collectors.  Sounds like the culprit, but the value is correct, I don't know why there is no drop through it.  I'm out of ideas, does anyone have a suggestion?

When in doubt, remember Ohm's law. One way to state that is: the only way a resistor can have zero volts across it is if there is zero current through it.

If it were mine, I'd wonder how the voltage from the emitter of Q5 ever gets through the compression control to pin 5. Everything in order along that path?

[mattthegamer463]

There seems to be something affecting Q3 Q4 and Q5.  There is no voltage drop after the 150k resistor which is directly connected to Q5 base and Q3 and Q4 collectors.  Sounds like the culprit, but the value is correct, I don't know why there is no drop through it.  I'm out of ideas, does anyone have a suggestion?

When in doubt, remember Ohm's law. One way to state that is: the only way a resistor can have zero volts across it is if there is zero current through it.

If it were mine, I'd wonder how the voltage from the emitter of Q5 ever gets through the compression control to pin 5. Everything in order along that path?

Things appear well on that path.  Nothing appears to be wrong with the potentiometer or the 27k connected to pin 5. 

Now, correct me if this thinking is wrong, but there is a 10uF cap connected to that 150k.  If Q3 and Q4 weren't doing anything the way they're supposed to, that cap would charge off current coming through 150k, and the voltage would eventually rise at that point to 9V.  Current can't likely be sourced from Pin 5 of the OTA so I doubt if theres any concern that damage was caused to the chip, I imagine.

I just tried swapping each transistor, inserting old ones as I went if there was no change, and there was no change in voltages.

[PRR]

> Q5
> E 9.1V
> B 9.1V
> C 8.5V

Q5 collector is (should be) connected to the SAME point as U1 pin 7. So should be the highest voltage in the box, 9.19V you say.

How is it over a half volt lower?

OR- have you confused Q5 Emitter and Collector? Collector at 9.1V (almost 9.19V) would be within normal slop.

When _NO_ signal, Q3 Q4 are off, 10uFd cap shouldn't leak DC. The only thing pulling down on the 150K resistor is Q5's Base current, which is very small. Top of 10uFd should be at 97% to 99.6% of supply voltage.

However the Emitter of Q5 should run one diode drop lower than the voltage on this 10uFd. Q5 current is small, but you expect 0.4V to 0.6V drop from Base to Emitter. (In fact, very similar to the drop on U1 pin 5 to pin 4, a "diode drop" with similar current.)

If you really have E 9.1V  B 9.1V, then there is nothing connected to Q5 Emitter. Verify the 27K resistor, and tack a 1K-100K fixed resistor across the Sustain pot end lugs to bypass a pot problem.

If you really have B 9.1V _E_ 8.5V, then Q5 appears right.

> Signal appears at the inputs of the CA3080 but not on pin 6.  Voltages are below.
> Pin 2 - 4.64V
> Pin 3 - 4.65V
> Pin 4 - 0V
> Pin 5 - 0.604V
> Pin 6 - 2.69V

3080 voltages are right. It's got power, inputs are in the working zone, pin 5 shows control current, and output isn't stuck. This suggests a non-functional '3080. Did you socket it?

[mattthegamer463]

> Q5
> E 9.1V
> B 9.1V
> C 8.5V

Q5 collector is (should be) connected to the SAME point as U1 pin 7. So should be the highest voltage in the box, 9.19V you say.

How is it over a half volt lower?

OR- have you confused Q5 Emitter and Collector? Collector at 9.1V (almost 9.19V) would be within normal slop.

When _NO_ signal, Q3 Q4 are off, 10uFd cap shouldn't leak DC. The only thing pulling down on the 150K resistor is Q5's Base current, which is very small. Top of 10uFd should be at 97% to 99.6% of supply voltage.

However the Emitter of Q5 should run one diode drop lower than the voltage on this 10uFd. Q5 current is small, but you expect 0.4V to 0.6V drop from Base to Emitter. (In fact, very similar to the drop on U1 pin 5 to pin 4, a "diode drop" with similar current.)

If you really have E 9.1V  B 9.1V, then there is nothing connected to Q5 Emitter. Verify the 27K resistor, and tack a 1K-100K fixed resistor across the Sustain pot end lugs to bypass a pot problem.

If you really have B 9.1V _E_ 8.5V, then Q5 appears right.

> Signal appears at the inputs of the CA3080 but not on pin 6.  Voltages are below.
> Pin 2 - 4.64V
> Pin 3 - 4.65V
> Pin 4 - 0V
> Pin 5 - 0.604V
> Pin 6 - 2.69V

3080 voltages are right. It's got power, inputs are in the working zone, pin 5 shows control current, and output isn't stuck. This suggests a non-functional '3080. Did you socket it?

Sorry yes, I must have mixed up the E and C of Q5. 

I did socket the CA3080, if you're suggesting I replace it, I don't have any more.  However all things do seem to point to it being the culprit.  Like I said, no signal ever comes out of it, which should be regardless of the state of the compression circuits (assuming the compression circuit isn't sucking the output to ground, which it isn't, since there is DC present)

[drummer4gc]

Again, hope it's all right to resurrect the dead instead of starting a brand new thread....

I've got a 1978 script dyna comp acting up. The signal off of pin 6 isn't quite dead, but heavily gated/distorted, like the battery is dead. My voltages appear correct after comparing them to the rest of the ones posted in this thread. The only ones that appear different are pins 2 and 3 of the ca3080, which read 1.30 (the emitter of q1 reads 1.46 - isn't this the voltage that feeds pin 2?) I'll post the rest if necessary, but I feel like I've got it narrowed down to the ca3080 being dead (I just don't have an extra one to test!). I just wanted to check if this sound is a reasonable symptom of a dead ca3080, or would a dead chip not let any sound pass at all?

thanks!

[R O Tiree]

A dead chip probably wouldn't pass any signal. More likely, perhaps, is the age of the pedal causing the electrolyitc caps to degrade. Replace those first and see what happens.