tonepad dynacomp help

[jason h]

Hello all-
   I'm having trouble getting my dynacomp working. I'm only getting a very weak signal and only when the sustain pot is maxed out. I've checked and re-checked all my part values and wiring. Both the IC and trannys are in sockets, so I don't think they got burnt up. I checked the diodes. Basicly, I'm stumped. Does any one have voltage readings for this project? Or mayby some words of wisdom?


jason h

[brett]

There are simply too many areas where a dynacomp could go wrong to try to diagnose it without some measurements.

Can you measure the voltages on the transistors and the ins and outs of the IC?  Double-check the pinouts and orientation of the transistors, too.  I still stuff them up.  

The other thing you could do is build an "audio probe" (as per other threads on this forum) and see where the signal is running into trouble.

[jason h]

Ok, I got some info. I took all readings with a new battery and power to the unit, but no signal.

trannys C      B      E
Q1       9.53  1.5   1.48
Q2       7.32  2.79 2.19
Q3       9.1    0      0
Q4       9.07   0      0
Q5       9.5    9.1   8.56

IC
in+ 8.56
in-  8.56
v+  9.3
out 2.73
bias 0.692

thanks
jason h

[jason h]

No one has any ideas where to start?

jason h

[Transmogrifox]

Well...

For one, you have a problem with Q1.

The base should be AT LEAST 3V, 4V or 5 V would be great.
and the emitter should be about .6 to .7 lower (Vbe = ~.6 V or ~.7V)

This tells me that you are using a low gain transistor for Q1....did you do any substitutions?  Try a 2N5089 if you have one, or darlington connect the ones you ARE using.

Q2 looks good, no problems there

Q3 and Q4 are fine, you will see this change as you play guitar (when it's working right)

Q5 measurements look good as well.

The IC voltages look bad:  in+ should be very close to in- which should both be close to 4.5 V +/- 1V or so

Giving the measurements definitely helps....so

Check Q1, and do what it takes to get the base at about 4.5 to 5V

Make sure Re is actually 470k (not 47k or 4.7k...that would give you those readings on the IC)

Make sure Rd is a jumper

Be sure that the two 1M resistors are connected to GROUND, not Vcc, and that the capacitors and that network there are all connected according to the schematic.

Everything else looks good, so I hope that helps!

[jason h]

Thanks T... I'll go start there.

I love this forum.

jason h

[MarkB]

and since it just happened to me - I'll throw in one other thing..

If you made the PCB yourself - MAKE SURE there aren't any TINY pieces of copper left shorting out traces.. sometimes they're so small you can only see them under a magnifying glass under bright light (and at certain angles!).

Measure across some of the components (for resistance) and  if something comes up as open that shouldn't - you've got a short.
"-)

[jason h]

Mark wins the big prize!!!!!!!!!!!!!
I just found the short this morning. A little solder bridge hidden under a big glob of flux. Transmogrifox was a huge help. He got me looking in the right area. The bridge was between Re(470k) and the 10k right next to it.
Thanks for the help guys.  I love this place

jason h

[MarkB]

Excellent!
Glad even a newbie-meathead like me can help!

SO how's it sound?
I built the same one off Tonepad and it sounds amazing.. I love it.   Doing artwork now so I can box it up.

"-)

[jason h]

It sounds great. I had aready built the ross, so its cool to hear the two side by side. The dyna will be great for clean lead work, and the ross goes great with my ts808 clone.  I'll put up some pics when I finish painting it.

thanks again for the help
jason h

[MarkB]

Stick the Ro/Dy mod on the Dyna... then you have both in 1 box with a switch... works great (then you can make one of your friends very happy with a gift of your spare one)
"-)