1974 "Bud Box" MXR Dyna Comp Help Needed

[GuitarFreak302]

Hello,

I'm not sure if this is the right place to post this but I have a 1974 MXR Dyna Comp that only passes signal in the bypass state. I have checked continuity between traces and everything is good. The pots and switch seem to be good also. I have taken the following voltages of the transistors and CA3080. I do not know what is wrong and your help would be appreciated. Thanks.

Q1.       C = 9.19
             B = 1.545
             E = 1.06

Q2        C = 7.27
             B = 2.399
             E = 1.853

Q3.       C = 9.03
             B = 0.00
             E = 0.00

Q4.       C = 9.02
             B = 0.00
             E = 0.00

Q5.       C = 9.15
             B = 9.01
             E = 8.58


CA3080 Metal Can

Pin 1 = NC
Pin 2 = 4.54
Pin 3 = 4.55
Pin 4 = 0.00
Pin 5 = .587
Pin 6 = 2.913
Pin 7 = 9.22
Pin 8 = NC

Thanks again.

[Kipper4]

What Schematic are you using so we can all work from the same song sheet?

[GuitarFreak302]

I am using this schematic as reference.

http://www.muzique.com/schem/dynacomp.gif

The transistors in mine are MPS5172

Thanks.

[Fender3D]

Assuming you have all wirings, pot and switch alive and kicking...

Short Q5's C and E.
if it works swap Q5 if it doesn't work swap 3080

edit:

just realized you have 8.58V @Q5's E and  0.587V @ 3080's pin 5: check there...

[GuitarFreak302]

I checked those connections and they are fine. I ordered a new Ca3080 and I will test it when I get it installed.

[GuitarFreak302]

I installed the new metal can CA3080 and there still isn't any sound when the pedal is engaged. Does anybody have any idea what could be wrong? Thanks.

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[thermionix]

Have you tried swapping Q5?

[GuitarFreak302]

I have not tried that yet.

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[thermionix]

I'm still a noob at solid state stuff, so I could be missing something, but those voltages you posted for Q5 make me think it may be shorted.

[Kipper4]

Well I just put the meter on my own and my Q5 voltage are around the same as yours.
initially the base and emmitter are smaller but climb to around the same as yours.
And your IC voltages are similar to mine.

[PRR]

Q5 voltages are correct. No signal, it pulls-up against the supply rail.

Where did you get the '3080?? We find a LOT of "fake 3080"s today. While a metal-can is a little less likely to be a re-marked phone-dialer(?) chip, do you really trust your vendor to know what he is selling?

[GuitarFreak302]

Q5 voltages are correct. No signal, it pulls-up against the supply rail.

Where did you get the '3080?? We find a LOT of "fake 3080"s today. While a metal-can is a little less likely to be a re-marked phone-dialer(?) chip, do you really trust your vendor to know what he is selling?

I got it from buildyourownclone.com

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[thermionix]

Sorry for the bad suggestion.    Not the first time one of the smarter folks has had to come around and correct me!

BYOC is a good source, I'm sure they sent you a good 3080.  I built their Ross clone kit, with the "vintage upgrade" parts, then later modded it from Ross specs to Dyna specs.  Sweet pedal.  I guess I should have measured the voltages in mine before commenting earlier.

[PRR]

Audio trace. Audio goes in, where does it stop?

[GuitarFreak302]

I figured out what was wrong and  I can't believe that I missed it. The output pot was shorted to ground. Everything works and sounds great now.

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[thermionix]

Woohoo!  Sometimes it's the simplest thing.