GuitarJack
New member
Well it was bound to happen eventually - finished a build, plugged it all in, hit the switch, and…. nothing. This is my fourth or fifth Isosceles Boost build, and the first i’ve run into problems with, so learning a lot on troubleshooting. Photos are from pre-reflowing.
TL;DR audio probe stops at the transistor base, and I'm not able to measure voltages to ground from anywhere except from the power input and LED anode.
TL;DR audio probe stops at the transistor base, and I'm not able to measure voltages to ground from anywhere except from the power input and LED anode.
- Made my usual replacement of the BC550 transistor for a 2N5210 installed backwards, otherwise all parts are per BOM. Capacitors are all at least 50 VDC so the charge pump voltages shouldn’t be an issue. Both ICs are socketed. There is an additional circuit you’ll see in the photos coming off the 4PDT for amp channel switching like the actual Grind pedal, no issues there.
- Bypass works, but when turned on dead silence, no hiss. Almost like it’s going to ground. LED comes on.
- Continuity through the switch and off board wiring is good, input jack tip to PCB input, and PCB output to output jack tip are ok. Grounds are connected.
- First reflowed all the solder points, then started tracing the board for continuity and checking components. For simplicity I kept it in Grind mode to cut out the tone stack pots. Everything in yellow in the photo was checked. Socketed ICs also show continuity from the IC to the solder points.
- Resistors all correct, except for R9 and R103, not able to get a stable reading on them. R1 and R16 were also reading off but in parallel with other components to ground, pulled R16 out and on its own measured correctly. It looks like R9 and R103 are in more extended parallel circuits so that is probably why they are off.
- 15817 diode reads 0.195 V forward voltage, and 1N4001 diodes all read ~0.592 V.
- 2N5210 transistor was tested in diode mode on my multimeter - base to collector is 0.706 V, based to emitter is 0.710 V, emitter to collector is OL, and collector to emitter is 2.5 V.
- Put together an audio probe and ran into no signal past the 2N5210 base - nothing comes out of the emitter or collector. If I squint I can hear the barest crackle at times on the emitter when the snare is hit on the songs.
- Bypassing the input jack and starting the audio probe at the center pin of SW1, I get a good signal to output jack tip, albeit attenuated in volume.
- Voltage checks - this is where I’m either just measuring it incorrectly or I damaged something in the circuit while building. I get 8.85V (older test battery) from both the power in and LED in to ground so that’s a start. But pretty much every other point reads either 0 V or incredibly low going to ground, ~0.01V. Same results with both of my multimeters. It’s like nothing from the power circuit is making it to the audio circuit, or even to D100. I can't see any bridges at the LED or power pads that would short like this. I thought the way to check voltage is black lead to ground and use the red probe to measure voltage of the components to ground? Or am I doing it wrong?
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