Cherrybomb troubleshooting

[VPIF]

Hi.

Cherrybomb, Madbean PCB, no sound when engaged, checked for solder bridges/cold joints.

Built a Cherrybomb last night, and have not been able to make it work. The voltages are way off (see below), and when I check for continuity, I find that the second leg of C1 is wide open to ground. I'm used to working on etched, single sided PCBs, where I can follow the tracks, but this is one of Madbeans PCBs, and I'm having a hard time figuring out which end of the component goes where.

Battery: 9.17V

Q1:
E: 0.15V
B: 0.0V
C: 8.18V

Q2:
E: 0.0V
B: 8.18V
C: 9.15V

Q3:
E: 0.86V
B: 1.47V
C: 5.76V

Any ideas? I'm starting to run out of them, so any help will be greatly appreciated. Thanks.

[jimilee]

What do you mean you don't know which side of the component goes where? (Don't mean to sound snippy of it does)Transistors flat side are usually marked as well as IC orientation and (+) sides of polarity components are usually marked. Be happy to help, also do you have pictures?

[midwayfair]

Look for a solder bridge at R3 and R4 on the left side of the PCB.

[VPIF]

What do you mean you don't know which side of the component goes where? (Don't mean to sound snippy of it does)Transistors flat side are usually marked as well as IC orientation and (+) sides of polarity components are usually marked. Be happy to help, also do you have pictures?

Sorry for not expressing myself clearly. I find it harder to follow the schematic/signal path through the PCB, as the traces are not as visable as on an etched PCB. All the polarized components are mounted correctly.

Look for a solder bridge at R3 and R4 on the left side of the PCB.

Yeah. There is definitely something going on in that area. One end og R2 is grounded, as it should. But one end of both R3 and R4 is also grounded (same end og R3 and R4, but oposite of the grounded end on R2 on the PCB) I have spent some time checking for solder bridges, visually and by scraping between the solder pads, but I cant find one. I am tempted to remove them, clean the pads and put them back in.

[VPIF]

I have lifted one end of R3 and R4 and cleaned up the solder, but the pads themselves are shorted to ground. The base of Q1 is still shorted to ground With R3 and R4 lifted. The gain pot has all the lugs wide open to ground when its turned fully clockwise. Could this be my problem? When the pot is tuned fully counter clockwise, lug 1 and 2 are open to ground, while lug 3 is not... Kind of puzzled here. I'm sure the solution is quite simple, but I can't seem to find it...

[midwayfair]

The gain pot has all the lugs wide open to ground when its turned fully clockwise. Could this be my problem? When the pot is tuned fully counter clockwise, lug 1 and 2 are open to ground, while lug 3 is not... Kind of puzzled here.

Look at the schematic. The gain pot connects to ground. This is not your problem. You need to inspect every connection to the base of Q1 to figure out where the short is. Remove them all one at a time if you have to, and if worst comes to worst, scrape off the solder mask with a knife and see if there's a fault in the PCB connecting something to the ground plane. Compare everything with the PCB image in the build doc.

[VPIF]

Following the schematic:

Input, C1 second leg connects to ground, R3 first leg connects to ground -second leg connects to R4 - which connects (correctly) to ground, and to the emitter of Q2 (which I thought would be open to ground, but it is not). I am allmost starting to suspect that the PCB could be the problem...

[VPIF]

Lifted C1, R3, R4, and removed Q1. Scraped the solder mask. The photo is not very good, but upon close inspection I can't see anything that looks like a copper/solder bridge. I have scraped a bit around the pads to try to make sure I wasn't missing a tiny piece of stray copper. And, yes, I have checked the top side of the PCB for solder bridges too.

Neither the non-grounded end of R4 (or R3), the positive side of C3, or the emitter of Q2 has got continuity to ground, so I haven't lifted those.

I claimed that I was running out of ideas in an earlier post, but now I'm really running dry. I'm sure I will be quite embarressed when I finally find the problem, but for now I'm kind of baffled.

[rullywowr]

I didn't see where you mentioned which brand/type of transistors you are using?  Can you elaborate on this?  BC109?

Did you double check them to ensure you didn't have an incorrect type in there?  Perhaps the pinout is different?

[VPIF]

Hi.

I used the BC109. Actually I wasn't absolutely sure about the pinout, as I haven't used anything but plastic encased transistors before, but I think I got them in the correct way. I tried turning them 180 degrees when I first realized that the effect didn't work.

Now I have, as stated earlier, removed Q1 and its socket, and I am down to the bare solder pads in the section of the circuit that seems to be the problem.

[rullywowr]

You should double check the orientation, its easy to mix this up when using canned transistors and you may have to cross leads over themselves (use heatshrink or insulation).  Looking at Q1 on the cherrybomb layout (with the flat side facing down) it is E-B-C. 

A BC109 pinout is this:

[VPIF]

Thanks for the image. Seems like I got it right the first time. Figured the emitter was the pin closest to the tab. Now, if I can only get the base of Q1 to stop shorting to ground, they should be fine the way i put them in.

[VPIF]

Finally got rid of the short! Partly because it was the only thing I could think of to do, and partly because I was getting rather annoyed, I used brute force and a sharp knife to cut along the tracks to the emitter of Q1, R3 and C1. And voila!

As it's well over midnight here I didn't take the time to put the box back together, but I guess it has a fair chance of working correctly this time.

Thanks for all the input, guys. I really appreciate it!