Scrambler troubleshooting

[chokeyou]

I was wondering if the green, rectangular .01mf poly film capacitors have poles?

I'm asking because my ampeg scrambler clone isnt working and i cant find a reason for it whatsoever...

[Jason Stout]

What do you mean by poles?

[Lonestarjohnny]

the small green poly caps are Bidirectional, they'll work no matter which way you install them, tou need to check and see what kind of voltage reading's your getting at the transister's and post them here, someone will help you trouble shoot it.
Johnny

[chokeyou]

I just discovered that my blend knob might be reverse 50K (though on my multimeter it reads closer to 60K w/ the red probe on pole 3 and the black on pole 1....then it reads closer to 30K with the red probe on pole 1 and the black probe on pole 3)...I think its a reverse pot because i get these values with the knob turned entirely counter-clockwise and its zeroed out when turned entirely clockwise.

I'm not sure how to read voltages with my multimeter yet, this is my second project (the first being the beginner's project here in the forum.) what setting do i want to use on my multimeter and where do i connect the probes?

[Jason Stout]

To measure voltage, set your meter to DC Volts,  connect the black probe to ground, and touch the red probe to the point in the circuit you wish to measure. About your pot, I'm not quite sure of what you are measuring but check out this page, It's the best page on pots I have seen yet.

[chokeyou]

what part of the transistor would i be connecting the red probe to, the emitter?

[Jason Stout]

Good question, measure the voltage at all pins, on all transistors and compare with the values on this page. You can check your jacks with your multimeter as well, use the continuity(beep) setting or the resistance(µ) setting to see if you have Ohmic continuity where you want to. (you want very low ohms)

[chokeyou]

well, Q1 is way off...what would be my next step in troubleshooting?

[Lonestarjohnny]

give us the voltage reading's on all 3 leg's of your first transister and we can help you
Johnny

[chokeyou]

off my power supply I'm getting 9.13 volts and heres Q1's legs... E=9.13 C=9.13 B=4.36 making me think E and C paths are connected somewhere?

[Fret Wire]

well, Q1 is way off...what would be my next step in troubleshooting?

Post the values to all four transistors. They can be interdependant on each other.

[sad mafioso]

While we're at it, does anyone mind if I throw out my own scrambler readings? (This is not intended as a threadjack.)

Q1: E: 3.45  B: 4.349 C: 9.09
Q2: E: .29  B: .915 C: 2.77
Q3: E: 3.48 B: 4.49 C: 9.07
Q4: E: 3.48 B: 4.48 C: 8.71

I'm concerned because B is more than a diode drop above E for Q1 Q3 and Q4. It was gating slightly until I changed two of the diodes to Ge.

[Fret Wire]

Your Q2 collector looks a little low.

[chokeyou]

Q1: E=9.13 C=9.13 B=4.36
Q2: E=.28 C=3.08 B.92
Q3: E=3.47 C=9.13 B=4.5
Q4: E=3.47 C=8.71 B=4.5

[Lonestarjohnny]

Choke, your's looks good except for Q1, you got a short maybe between emitter and collector, turn the power off and do a continuity test between them, it should show if it's shorted or not, and your sure your tranny is oriented properly,
Til tomorrow.
Johnny

[Jason Stout]

Choke, your's looks good except for Q1, you got a short maybe between emitter and collector

I agree, sometimes the short is easy to see, and sometimes the problem connector approaches microscopic size. Good luck!

Also - Can you post (or send me) a picture of the front and back sides of the board?

[chokeyou]

i found the short...it was a microscopic string of solder connecting 2 traces but the pedal still doesnt work.
here are my current voltages

Power supply = 9.13
Q1: E=3.45 C=9.13 B=4.35
Q2: E=0.29 C=3.05 (low) B=0.92
Q3: E=3.48 C=9.13 B=4.5
Q4: E=3.48 C=9.13 B=4.48

I'm still wondering about my blend pot...it could be reverse from what i've measured. I'll have pics up in a short while.

[chokeyou]

top of pcb:


bottom of pcb:


enclosure wiring (color coded):

[sad mafioso]

There is an error in the tonepad schematic, and the polarity of C3 should be switched from the way you have it. See http://www.diystompboxes.com/sboxforum/viewtopic.php?t=25050 and http://www.diystompboxes.com/sboxforum/viewtopic.php?t=11286.

[chokeyou]

thanks for pointing that out, i had no idea.
now i turned it around and im getting signal with the effect engaged...im just not getting quite as much gain as i should be (i think) also the knobs have very little purpose...only the end of the blend knob affects the tone