No output on M800

JetFixxxer

Active member
Let's recap what we saw/heard in the video. When you probe the bottom end of R3, which is supposed to be ground, you get the same signal as when you touch the input on the footswitch. How is your board grounded? I'm thinking it's not. I see a black wire dangling and another one going to a lug on the output connector, but I can't tell if it's the correct lug. Where is your audio probe grounded?
The wires dangling one comes from the TWILL PCB and the other is the PCB of the M800. Which when I first completed the build the Twill was grounded to the output jack and the M800 was grounded to the input jack.

The probe I ground to the enclosure or the ground on the output jack. I've also just grounded the dangling wires to the enclosure as well.

The Twill works without issues.

I get 9.1v to the PCB.
 

Chuck D. Bones

Well-known member
And the problem with the M800 still exists? I'm trying to figure out how you got a tone in your audio probe when you touched the ground end of R3.
 

JetFixxxer

Active member
And the problem with the M800 still exists? I'm trying to figure out how you got a tone in your audio probe when you touched the ground end of R3.
Twill works M800 Doesn't.

I don't know why I'm getting tone on R3. I took a 20x Jeweler loupe and check all the solder joints on the bottom of the PCB. Everything looks good no bridges of solder to terminal. Cleaned it again with alcohol with a toothbrush.
 

Chuck D. Bones

Well-known member
Can you measure the resistance from the bottom end of R3 to the ring of each jack? Not the terminal, the actual ring on the outside of the box. Also provide an updated photo if you did anything to change the wiring.
 

JetFixxxer

Active member
.5 Ω to both the input and output jack from the bottom end of R3. This is assuming bottom end is toward Q2. . Top end I get around 25MΩ.
 

Chuck D. Bones

Well-known member
You were touching R2, not R3 like I had thought. This troubleshooting by remote control is tricky stuff! Hard enough to do when you're there.
The signal on R4 was very weak. Does Q1-D (pin 1) sound the same as the bottom-end of R4? Q1's drain voltage was good the last time you reported it. Maybe C2 is bad or has a bad connection. Check the resistance from pin 1 to pin 3 on the GAIN pot. Should be 1Meg with the GAIN set to 0, 5 or 10.
 

JetFixxxer

Active member
GAIN pot 0, 5, and 10 = .976mΩ.
Very low tone on the drain of Q1. Have to put my ear to the speaker to hear it. It's lower than R4. Drain 5.6v.
Will check C2 and see if that's it.
 

Chuck D. Bones

Well-known member
Little "m" is usually reserved for "milli," capital "M" signifies Meg. I'm gonna go out on a limb and assume you meant 0.976M as in 976K. No signal on Q1 drain, but drain has the correct DC voltage. Hmmmmm...
Maybe Q1's gate is shorted to ground or source? Measure resistance from Q1-G (pin 3), or the top end of R2, to ground.
 

music6000

Well-known member
Little "m" is usually reserved for "milli," capital "M" signifies Meg. I'm gonna go out on a limb and assume you meant 0.976M as in 976K. No signal on Q1 drain, but drain has the correct DC voltage. Hmmmmm...
Maybe Q1's gate is shorted to ground or source? Measure resistance from Q1-G (pin 3), or the top end of R2, to ground.
That's why It would be Good to see a Pic of the back of the Board!!!
I been thinking Solder bridge on Q1 socket.
 

PKRPedals

Active member
I hope you get this working. I have built 2 of them and neither one worked out for me. I get sound but it is terrible. Good luck.
 
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