Build Your Own Clone Message Board

Hey guys. Built this a while ago, and got a bit cranky with it, so left it alone. Time to try again though.
Boost works. (Yay). LED for overdrive channel works. So power at the switch then. :S When volume maxed, hear a little bit of noise. Nothing really musical though.

Op amp voltages...

1 - 4.53
2 - 4.54
3 - 4.53
4 - 0.0
5 - 4.53
6 - 4.65
7 - 4.53
8 - 9.07

Input transistor:
Top - 9.08
Mid - 4.16
Bottom - 3.77

Output transistor
Top - 9.07
Mid - 4.14
Bottom - 3.74

Continutity eyelet 4 to bottom leg R1 0.4 ohm
Continutity eyelet 8 to top leg R14 0.4 ohm

With a signal tester:
Center pin of Q1 = Clean
Bottom pin of Q1 = Clean
Pin 5 of IC1 = Nothing
Pin 7 of IC1 = Nothing
Pin 3 of IC1 = Nothing
Pin 1 of IC1 = Signal but crackly and not very loud
Center pin of Q2 = Signal but crackly and not very loud
Bottom of Q2 = Signal but crackly and not very loud

The outside leg of the level pot and the middle give the same signal. Weak, crackly.

Tried the other op-amp that came with the kit, and was able to pick up AM Radio (a local station. 2BS Bathurst, if you must know. ), but still signal is weak and crackly.

Please help me. I like the radio, but not through my amp. :S

btw: Will try to get a couple of shots of the board as soon as i can.

bump... sorry

Op-amp voltages look good.
Transistor voltages also good.

The 'eyelet' measurements don't tell us a lot because as far as i can work out you just measured the continuity of the short length of PCB track from the input and output resistors to the 'edges' of the PCB - what you really want to know is are the input and output paths continuous from the input and output of the circuit - through the foot switches - to the tip contacts on the input and output jack sockets.

Signal trace - input signal gets through Q1 OK but signal is not being correctly amplified by IC1a so your problem lies around the first op-amp. Where have you set your trimmers? Oh wait .. they seem to be at sensible settings.

Actually now I think about it you should have a strong signal on pin 3 / R7. Check the solder joints (both sides of the PCB) around that point and take a close look at C2 (a 1uF), I suspect signal is not getting through that cap.

Oh POX! hold on a minute the OD2 seems to be yet another BYOC kit where the pin numbers on the circuit diagram for the two halves of the op-amp are the reverse of what they are on the PCB - so IC1a is pins 5,6 and 7. IC1b is pins 1,2 & 3. So you should have a strong signal on IC1 pin 5 / R7. My previous comment about C2 still holds - signal does not appear to be getting through that to reach pin 5. C2 is the large white cap just below where it says 'drive' on the PCB overprint.

Kept at it and would you believe I found it. Should have taken a photo of it... Sorry.

You were right, it was C2. The joint looked fine, and I reflowed the solder just in case, but when I put the audio probe on the other side of the Cap, and then sort of jiggled the cap, you could hear it crackle and pop intermittently. Yanked the cap out, and the bottom pad looked almost white. I'm guessing I almost burnt out the pad. Re-installed the cap, more solder (hoping that the pad stays put), and it works. Yay!!!

Now to figure out the earth hum it's got. If I touch the enclosure it's fine. If not, it hums when the overdrive is on. Any ideas where to start looking? (Search obviously, going there now.)

I'd guess the case is not grounded properly. It should get its ground through the sleeve connection of the input socket which is wired to the circuit ground on the PCB. The output socket only picks up its ground through the case. This is no problem on a bare metal case but sometimes painting a case can result in poor ground connections for these jacks.

Either that or your guitar is not grounded properly.

As to the pad I would guess that when you un-soldered the cap you did not transfer enough heat to the top surface of the pad (it is not easy to get the solder melted all the way through a plated through hole like that). When you pulled out the cap the solder on the top pad under the cap was only barely melted which left a granulated crystalline surface that as you say looks almost white. The pad is likely perfectly OK.

It may not be a factor for your hum problem at all, but I would rotate your output jack maybe 10 - 20 degrees or so CCW to insure that the solder tab for the tip is completely clear of the adjacent screw boss of the enclosure. Looks awfully close in that first photo.

Thanks guys. Pleased to know you're still willing to impart your wisdom to dummies like me

I'll keep on building.