Cornish G2 Clone troubleshooting Help? No output with no noticeable culprit

[Bandwagonesque]

Hi everyone.

Sorry for the long write up but figured I'd be as concise as possible to whomever can maybe help me see the error in my ways. I've been slamming my head against a wall in trying to troubleshoot a Pete Cornish G-2 clone I built nearly a year ago but to no avail. When I initially built it, it didn't work with the first layout I tried and after exhausting all my knowledge (little) in trying to find what was wrong, I went the fools route and decided to build it again, this time with different layout to work from.

Unfortunately, I ended up in the same place I started in that my second try didn't work just like the first. It bypasses fine, but when engaged it doesn't seem to make a peep although if I have my amp turned way up,  I can hear the controls faintly alter the hum of the amp/guitar. Volume turns the hum up and down, and the filter seems to color the hum too. The fuzz control, I can't hear it doing a thing. But alas, no fuzz or output of any kind.

I then went about checking the layout to my build (layout attached, I used the buffered layout), making sure everything was in its right place. All resistors were of the right value, all caps and diodes and transistors had the right polarity and placement and pinout. My wiring and grounds seemed to be right on point. All trace cuts and jumpers were correct. No trace bridges anywhere after illuminating the circuit with a lamp. Continuity between all leads and connections is good. For the life of me I couldn't figure out what was wrong and decided to stick the build on the shelf for another day/month/year to revisit again with a clearer head.

I finally dusted the build off this weekend hoping to unearth what I overlooked initially but still cannot see any superficial errors in my build at all.

What I didn't do the first time was audio probe and test voltages of the transistors. First I audio probed from the input through the buffer circuit. No issue there. I then went ahead to the main board and got as far as the 5th bus from the bottom. It seems that the collector for the transistor on that bus and everything else falls silent from there.

I guess my problem lies in where I go in figuring out what component could be the bad one of the 5 attached to that bus. I'm not even sure if I'm on the right track to be honest as my knowledge is still really limited. I then checked the voltages of the the transistors to see if that could narrow things down and this is what readings I pulled. (if looking at the Vero layout attached, first transistor towards bottom, then going counter clockwise. )

T1:  C: 9.15      B: 6.00      E: 5.48
T2:  C: 0.98      B: 0.98      E: 0.36
T3   E: 0.03      B: 0.63      C: 3.96
T4.  E: 1.13      B: 1.73      C: 5.01
T5:  C: 8.79     B: 0.49       E:  0.00



I measured the leakage to the transistors while at it and noticed that they all ranged around hFE 500. Is this too high and could this be the issue?

I'm still kind of left scratching my head as there isn't anything obviously wrong to my untrained eye. I'm just unsure what to do with this information though something must be wrong. Can anyone see what may be amiss from the readings posted?

Heres some pics of my build (really wish I used color coated wire in retrospect, sorry guys). I have the ground sent to the enclosure due to the types of jacks used. Otherwise I don't see anything in the build touching where it shouldn't be (there is good clearance beneath the main circuit and the pots underneath). Thanks for any help folks as any would be greatly appreciated in finally getting this build working as I feel i'm real close as is. Getting this to work with as much time put in so far has been a drag with no noise to show from it so thanks for at least reading if you've gotten this far.
















*I myself see some suspect spots on the underside of the board after taking this photo. I went ahead and cleaned them and checked the continuity and all is well. still doesn't work 

[Slowpoke101]

T2 (which ever that one is... ) seems to be of the most interest. You have the same voltage recorded for both the Collector and the Base. A short circuit would be the most likely suspect so have a good look for a solder bridge or loose piece of wire.
Also noted a resistor that seems to have been installed with the incorrect value. Check the picture below;

[Slowpoke101]

And referring to the short that I mentioned - here it is;

[duck_arse]

what I can see ......


not sure where they are in your topside, my eyes hurt too much, especially without a circuit diagram. even if these are the problems on this build, doesn't fix the first build, does it? how much clearance do you have between the jack fingers/dingers and the metal of the case when a plug is inserted?

[Bandwagonesque]

Hi slowpoke. thanks for the reply. I had forgotten to mention that between the 2 layouts I listed, aside from the obvious with one being buffered and the other non-buffered, theres some other changes between them. Theyre subtle and it appears the buffered one has that resistor as a 680ohm while the other is 100ohm. Another difference is the placement of the 39K resistor on the other side of the resistor you mentioned. both near the input. you can see the 39K takes a hop between layouts in being connected to the 1m resistor at the input in the buffered layout, and the 47nf capacitor in the other. Now that I mention these, could this be an issue? I followed the layout (the buffered one) down to a t so im unsure what is up but it seems other people have built the layout with no issue.

I checked out that spot you mentioned on the bottom of the board and it may be an anomaly in the photo, but I did go ahead and clean traces up and then measured continuity between buses and where there shouldn't be any and didn't come up with any blips or bleeps.

gonna keep at it but thanks alot for the help and hope maybe the weird difference in components may be a lead to my problem overall

[Slowpoke101]

Another difference is the placement of the 39K resistor on the other side of the resistor you mentioned. both near the input. you can see the 39K takes a hop between layouts in being connected to the 1m resistor at the input in the buffered layout, and the 47nf capacitor in the other. Now that I mention these, could this be an issue? I followed the layout (the buffered one) down to a t so im unsure what is up but it seems other people have built the layout with no issue.

Ummm......Yes, it most likely is the issue. By moving that 39K resistor you have actually disconnected the input buffer and loaded the base of the transistor (T2 ? ) next to it with 39K to ground.....Put the resistor back to where it is shown in the tagboard layout "Cornish G2".

[Bandwagonesque]

Thanks so much for your help you guys. It is really really appreciated. slowpoke, you were right on the money with the resistor being in the wrong spot. Once I moved that and conditioned my traces for any almost out of sight bridges, it cooked right on up. Had to replace the diodes but after that it sounds just like it does on the demos and really sings. Wish I came about that resolution sooner as it was rather obvious after all (couldve sworn i tried this fix way back but must've had another kink somewhere) but very happy now after your help so thanks again.

To not make another thread and take up space, one weird thing though I noticed after I built this. And the same issue occured with my ss2 cornish clone built very much the same approach. Both builds implement the cornish buffer and are wired and dressed much the same in the gut shot provided. Kind of a big enclosure (using the same as pete did) so the leads are a bit longer than they need to be. Anyways, the problem with both is that there is bypass bleed. And it seems to be able to be manipulated with the volume knob (volume all the way up and the distortion bleeding through is at its peak, wind it back down and its not that noticeable, but still there. I've been powering both with their own 9v 1 spots during testing.

I realize that this could likely be remedied simply by not using the buffer and true bypassing each but didn't want to put the buffer circuits to waste (daughterboards). Anyone know what could be amiss with each build?

[r080]

Does it go away if you move the wire from the buffer output away from the volume pot output wire? Does the SS2 clone have those two wires in the same spot?