Rocket Fuzz Issues Again....Help Please

[lerxstlover]

Well, after figuring out my first build of the Rocket Fuzz (with everyone's help) I decided to make a more compact board (I gave myself extra space the first time) to fit inside my enclosure (3.75" x 3.75" electrical outlet box) and of course it's not working.  Works fine in bypass, but nothing when effect is turned on.  Here is the layout based off of R.G. Keen's layout on GeoFex.  I rearranged and compacted it to get it on a smaller board:



I traced the signal with the signal trace tool built from a 1/4" jack and get sound all the way to R10.  I switched out Q3 and the trim pot and still no good.  I've gone over the board and cannot find any solder bridges.  I socketed C1, C2 and C3.  I've check my trace paths against the original and I think I have everything connected the way it should be (or maybe not, since it's not working  )  The extra solder pads around the caps are for sockets.  I've been trying to debug it for over 4 hours now and I think I'm to the point I'll do more harm than good.....

Anyway, here are the readings from the board.

Voltage at the circuit board end of the red battery lead = 8.5V

Q1
C = 8.5V
B = 4.22V
E = 4.90V

Q2
C= 0V
B= 0V
E= 0V

Q3
C = 0V
B = 0V
E = 0V

C1 (I'll just say top and bottom on these)
top = 0V
bottom = 4.22V

C2
top = 0V
bottom = 4.88V

C3
top = 0V
bottom = 0V

C5
top = 8.47V
bottom = 8.48V

C6
top = 0V
bottom = 0V

C7
left = 0V
right = 0V

C9
left = 0V
right = 0V

These two are the electrolytic:
C4
+ = 8.48V
- = 0V

C8
+ = 0V
- = 0V

R1
top = 8.48V
bottom = 4.22V

R2
top = 0V
bottom = 0V

R3
top = 4.22V
bottom = 0V

R4
top = 8.48V
bottom = 0V

R5
top = 8.48V
bottom = 4.59V

R6
top = 8.48V
bottom = 8.48V

R7
top = 0V
bottom = 0V

R8
top = .0V
bottom = 0V

R9
top = 0V
bottom = 0V

R10
top = 0V
bottom = 0V

Thanks again!

[R.G.]

Clearly, Q2 and Q3 have problems. With all the pins at 0V, they're either shorted to ground, open to +9V, or a combination of both. Well, the third and always lurking possibility is a measurement error, but that's always with us.

I started at Q1. R1 and R3 are a voltage divider across the DC power. The junction, at Q1 base should be at 9V*1M/(1M+0.47M) or about 6.12V. Your battery is only 8.48V under load per your measurements, so we might see 8.48* 1000/1470 = 5.76V. Further, both R1 and R3 have a 5% tolerance, and if that happened to be maximum and both in the wrong direction, you could get 5.19V. So the base voltage at Q1 is low. Not dramatically, but low.

The emitter of Q1 should be roughly 0.6V lower than the base. It's 0.7V higher. Measurement error? Confusion of Base with Emitter leads? However, you also list R4 as having 8.48V from top to bottom. If it's connected to the emitter of Q1, it should have the same voltage across it, 4.90V. So something is messed up there, either the PCB, soldering, or voltage measurement. You also list C2 as having 4.88 V at its bottom, so I'm inclined to thing you had a typo on listing the voltage across R4 and it really is 4.88 to 4.9V and there is some other error in measurement of the base. But it doesn't feel right, and I pass on just because you heard audio and because there are other more pressing issues.

Let's jump to the output, Q3. Q3 shows 0V everywhere. Cross checking on the parts connected to it, we see C8 at 0V, R7 at 0V on the collector, and Q2 collector at 0V on the base. But R5 shows what should be the same voltage as Q2 collector at 4.59V. PCB open? Solder joint open? Erroneous measurement?

Looking at R7 we see 0V at BOTH ends, and on R6, 8.48V at both ends. My best guess here is that R6 is connected to the battery, and R7 is not connected to R6. That keeps any current from getting to Q3's collector and would keep any audio from getting through. With power off, check the continuity of top of R7 to top of R6 with an ohmmeter ON THE LEADS OF THE RESISTORS not on the PCB traces. I think that it will be open. Fix that and let's see what you have.

[lerxstlover]

Hi R.G.,

Yep, it was open. Fixed it along with another loose solder and now I get signal all the way to the output, BUT....

I tested the signal using a drum machine and it works great all the way out.  However, when I connect the guitar there is no signal (actually it's a BARELY audible signal if you turn the amp up.)  This happens after C8.  The signal really falls off at C9.  I realized the reason the drum machine is working and not the guitar is that the dmachine is an active signal.

SO, I replaced C9 and voila!  We're back in business.

Thanks again for your help!  Like I said, I need to quit working on these things until 4 a.m.  Always better to get a good night's sleep and start fresh.