Dynacomp, another failed project?

[Milotic]

Hi guys

I thought i would give the Dynacomp a third attempt and it failed again.
Switching worked fine and got a good bypass signal, but nothing when the comp is on.
I used a tonepad Dynacomp PCB

Voltage readings:

IC, CA3080E
1 - 0v
2 - 3.93v
3 - 3.93v
4 - 0v
5 - 2.44v
6 - 2.61v
7 - 9.55v
8 - 0v

Q1 2N3904
C=9.54v
B=1.34v
E=1.66v

Q2 2N3904
C=7.20v
B=2.48v
E=2.26v

Q3 2N3904
C=8.23v
B=0
E=0

Q4 2N3904
C=8.14v
B=0.04v
E=0v

Q5 2N3904
C=9.54v
B=8.15v
E=8.71v

D1 1N914
A=9.54v
K=0

D2 1N914
A=0
K=0

D3 1N914
A=0
K=0


Any help would be appreciated.

[petemoore]

  Q1 2N3904
C=9.54v
B=1.34v
E=1.66v
  This is a gain stage ?..the the emitter needs to be one Si [like the B/E diode in 2n3904] diode voltage drop above the emitter to be in bias.

Q2 2N3904
C=7.20v
B=2.48v
E=2.26v
  The emitter is at least above the base on this one.
Q3 2N3904
C=8.23v
B=0
E=0
  Here the base seems to be stuck on Gnd., as does the Emitter.
  Since the collector has a + type V on it, suspect the base or B/E are somehow cmisconnected to Gnd.
Q4 2N3904
C=8.14v
B=0.04v
E=0v
  See what Q4 and Q3 have in common as far as bias arrangements/to power rails, that might related to the O.Volts they have in common.
  Q5 2N3904
C=9.54v
B=8.15v
E=8.71v
  This one looks like the emitter resistor to ground is open, allowing the emitter to floate way up near the + rail, ...above 1/2v.

[R.G.]

IC, CA3080E
1 - 0v
2 - 3.93v
3 - 3.93v
4 - 0v
5 - 2.44v
6 - 2.61v
7 - 9.55v
8 - 0v

This all by itself is enough to keep it from working. Pin 5 is the bias current input for the ca3080 or lm3080. It cannot be more than 0.7V above the negative power supply if the chip is working properly, just by the nature of the internal circuit. This one shows 2.44V. Either the chip is no good, or the connections to the pin are bad. Either way, the chip cannot pass audio.

There may be other problems, as Pete notes. Get the chip voltages right first, then we can work on the other things.

[Milotic]

Thanks MR Pete and Mr R.G. for the replies.

@R.G.  I started with your post and i traced the tracks to and from pin5 of the IC.  And! I found some lead splatter connecting the Emitter from Q2 to Pin5.

Tomorrow, Since its midnight now, i will try and fix this issue and hope it resolves this issue.

Thanks Lads.

[R.G.]

... i traced the tracks to and from pin5 of the IC.  And! I found some lead splatter connecting the Emitter from Q2 to Pin5.

Good detective work! There is a chance that you'll have to replace the IC, since more than 1ma into pin 5 can kill that chip. We'll know more when you get a chance to clean it up a bit.

Sleep well... 

[Milotic]

Hey

I recently just fixed the issue and took another reading.
At first, the chip fluctuated between 0.6-3ish volts before it stopped at around 7.59v.
Based on that, I am concluding that this chip is broken.
Now i have to wait for about a month until futurelec delivers me some CA3080E's.

Thanks for the help RG.