GGG Small Stone debug

[Cardboard Tube Samurai]

It is with great frustration that I come to you for assistance. This effect has been my White Whale. Nearly a year ago I built one of these and spent many, many hours debugging the thng. A year later, after attempting to debug it again, I gave up and built an entirely new one. Yet again, it has failed me. Are there any known problems with the layout ( http://www.generalguitargadgets.com/pdf/ggg_smallstj_lo2.pdf) at GGG? I made my own PCB. I used PN200s in place of the 2n5087s and a BC549 in place of the 2n5088. I have also tried BC557s in place of the 2n5087s but also got nothing from the effect (2n5087 and 2n5088 are pretty hard to source in my area). I'm getting absolutely no signal at the output of the circuit

Someone please help me debug this darned thing.

Here are my voltage findings:

9.06V (battery)

IC1:

1 - 0
2 - 0.3
3 - 0.3
4 - 0
5 - 0.76
6 - 0.15
7 - 0.76
8 - 0.77

IC2:

1 - 0
2 - 0.29
3 - 0.3
4 - 0
5 - 0.76
6 - 0.13
7 - 0.77
8 - 0.77

IC3:

1 - 0
2 - 0.31
3 - 0.3
4 - 0
5 - 0.76
6 - 0.76
7 - 0.76
8 - 0.76

IC4:

1 - 0
2 - 0.31
3 - 0.3
4 - 0
5 - 0.76
6 - 0.07
7 - 0.76
8 - 0.76

IC5:

1 - -0.08
2 - 0.18
3 - 0.73
4 - 0
5 - 0.17
6 - 0.76
7 - 0.77
8 - 0.73

Q1:

E - 0.77
B - 0.29
C - 0.01

Q2:

E - 0.77
B - 0.77
C - 0.01

Q3:

E - 0.73
B - 0.18
C - 0.73

Q4:

E - 0.73
B - 0.73
C - 0.18

[Cardboard Tube Samurai]

Anyone?

[mdh]

I don't have time to check this assumption at the moment, but I'm assuming that the pinouts of the OTAs are the same as for the 3080s used in the tonepad version of the project (and I'm also going off of that schem, because the ggg one is really hard to read).

It looks like your bias voltage is way off.  I think pins 2 and 3 should be sitting somewhere much closer to 3-4V.  Maybe you have an incorrect resistor value or leaky electrolytic cap in the bias network?  On the tonepad schem, this is the voltage divider made up of a 15k and 10k resistor and the associated 33uF cap, right near the battery.

Edit: I also notice that the highest voltage in your list is 0.77V, and that's the voltage that's seen on the supply pins of the ICs (pin 7).  You didn't happen to mention the in-circuit battery voltage, and whether the battery is getting warm.  If that's the case, again it could be a leaky electrolytic cap (this time, one across the power rails would be the prime suspect, if there is such a cap), or any number of other problems that lead to a short or near-short across the power rails.

[Cardboard Tube Samurai]

Thanks for the reply. I've popped one leg of each of the aforementioned resistors out and they are correct (10 and 15k). I have no way of testing the cap though as my meter's capacitance only goes to 20uf range. I was silly enough to post the in-circuit battery voltage in my first post and the actual voltage of the battery (out of circuit) is 9.16. No, the battery doesn't heat up at all and I have checked it a few times to be sure.

I've just noticed that in the schematic on GGG there is no 470 ohm resistor, however there is one in the layout directly inline after the 9v+ in. I'm going to jump it and see what happens.


*EDIT*

I bypassed the 470r resistor and got sound through the effects, but it wasn't phased at all. I went to check the voltages again and realised that the battery was heating up so immediately disconnected it. I checked the ICs and they were getting warm too

[mdh]

Have you verified the orientation of the ICs?

[MadMac]

Ahh my Jaycar friend - we finally meet online

I agree with mdh - it sounds like a power supply issue assumming that you have checked the obvious i.e.

1.  that the IC you are using has the same pinout
2.  all your other part subs have the same pinout

I would check the data sheets on your subs against the ones listed on GGG and also check it against the Tonepad schematic.  http://www.tonepad.com/getFile.asp?id=7

I have been caught using similar IC's and fets with different pinouts.  Sometimes they can be different between manufactures.

Also assuming you have used sockets - Pull out all of the IC's and then remeasure your voltages - at least that will give you a chance to see if there is a fault with the voltage divider circuit.

[Cardboard Tube Samurai]

Hello valued customer! 

All ICs and transistors are oriented correctly. I think in the year or so since I started the original one of these, I have checked the pinouts and orientations somewhere upwards of 1300 times.

I did as suggested and took the ICs out to check voltages and that seems to be where the problem is. Just on IC1, the voltages were much closer to (what I suspect is) a reasonable working voltage. When I replaced IC1, the voltages dropped again (though I only checked them on IC1)

I'm suspecting grounding issues but I have checked these things upwards of 1300 times too  . Can someone please pass an eye over the GGG layout (link in first post) and tell me where they would put the wire to "offboard ground"? I have put this to the input ground. In fact, everything has a common ground offboard

[MadMac]

Ground connection should be fine  connected as per ggg layout.  Please tell me your not using metal power jacks

[Cardboard Tube Samurai]

Dude, give me SOME credit here. In any case, it's not even housed yet so it's not shorting to the enclosure.

[MadMac]

Dude, give me SOME credit here. In any case, it's not even housed yet so it's not shorting to the enclosure.

Not meaning to offend but both builds have the same fault?  The metal jacks had me stumped for about 12 months I think   Bought them cause I thought they looked cool then finally realised as soon as they were boxed  up bup booh.

I usually find that when mine don't work at all it can be as simple as a wiring mistake.  But I I still think in your case its something with the power supply or a short. The voltages have to be right at Vbias.

Im sure you'll get there!

ps my thor matched fets no fix. ho hum its back on the to be raided for parts pile.

[mdh]

So, you're using CA3094s, and they're definitely oriented correctly?  Is it possible that they were oriented incorrectly at some point in the past and got cooked enough to fail shorted?  Looking at the pinout and the schematic, flipping the orientation of the IC would put Vb on pin 7 (V+) and 9V on pin 4 (gnd).  This would put a reverse voltage close to half of the supply across the supply terminals, and could be enough to cause the chip to fail.  If I were you, I'd test out the ICs using one of the datasheet test circuits on a breadboard.  If they get hot in a nice simple test circuit, you're either mistaken about the pinout, or you've cooked them.

It just seems to me that if the voltages are reasonable until you put in an IC, then something must be wrong with that IC, or there has to be a short or bad component (or component value) in the neighborhood of that IC.  Perhaps a test for the latter situation would be to check the voltages with only one IC in the circuit, moving that IC around to each of the sockets in turn.  If one of the sockets causes a problem and the others don't then there's probably a problem near that socket.  That's kind of ad hoc, but it's the best I can come up with, aside from the comments above.

Failing any success with the above approaches, I think we're getting into photographic evidence territory.