M800 - No Volume

[DrumBuster]

Hello everyone, after neglecting my project for almost a year, I finally built my M800, when trying it out, I noticed I had no volume. Bypass works great, j201s all biased to the right voltage (4.5v ish) save for one of them not doing it. It stays stuck at 2.7, is it possible that is the culprit? I got a 2N5458 just in case is a faulty transistor. I check every solder and ground and everything seems fine, led lights up. What it can be the issue? Thanks

 

[DrumBuster]

If you Google "audio probe pedal" videos will come up, along with how to make them. Cap size isn't too important, any size cap above 10n to 220n will work. It's primary purpose is to keep DC from being passed to the amp if you touch the wrong lead.

Hello, I used the meter. Q2 doesn’t seem to be on spec, when I have the trim pot at the minimum, it reads 0.005 on drain, when is on the right, it reads 2.5

 

[DrumBuster]

Hello, I used the meter. Q2 doesn’t seem to be on spec, when I have the trim pot at the minimum, it reads 0.005 on drain, when is on the right, it reads 2.5

Tried everything regarding continuity and everything seems alright

 

[music6000]

Hello, I used the meter. Q2 doesn’t seem to be on spec, when I have the trim pot at the minimum, it reads 0.005 on drain, when is on the right, it reads 2.5

Mark the suspicious J201 & SWAP it with a Good J201 & see if it is Good in Q2.

 

[DrumBuster]

Mark the suspicious J201 & SWAP it with a Good J201 & see if it is Good in Q2.

Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?

 

[music6000]

Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?

You need to swap it with One that has bias Good in the Pedal to make sure you don't have an issue in Q2!

 

[music6000]

You need to swap it with One that has bias Good in the Pedal to make sure you don't have an issue in Q2!

Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?

This is my Only request/ suggestion:

MMBFJ201 JFET (Pre-Soldered) - PedalPCB.com

JFET

www.pedalpcb.com

 

[Chas Grant]

Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?

Mouser has them, but they are expensive. music6000's suggestion is cheaper.

 

[Chas Grant]

These are the generic drain voltages that others are shooting for on this circuit. They may be helpful
Q1-3.78V Q2-6.85V Q3-4.02V Q5-5.6V Q6-2.7V

 

[DrumBuster]

These are the generic drain voltages that others are shooting for on this circuit. They may be helpful
Q1-3.78V Q2-6.85V Q3-4.02V Q5-5.6V Q6-2.7V

Oooh, didn’t know they sold smd to to92 pre soldered.

 

[music6000]

These are the generic drain voltages that others are shooting for on this circuit. They may be helpful
Q1-3.78V Q2-6.85V Q3-4.02V Q5-5.6V Q6-2.7V

I built the first M800 way back, It worked but I knew something was wrong with the lack of sustain:

M800 Overdrive

Awesome JCM800 Emulation !!! All the Trimmers were adjusted to 4.5v & it was meh, 4.75, 5v, 5.25v & 5.5v, Louder with no Gain! Old School, Strummed a Chord & tuned each Trimmer by ear. Critical Trimmer is the Tone trimmer, This effects overall EQ & gives it the Power of The JCM800 sizzle! The...

forum.pedalpcb.com

 

[DrumBuster]

Ordered 8 PF5102, based on Chuck’s recommendations in a thread, I bought 8 just to be sure.

 

[music6000]

Ordered 8 PF5102, based on Chuck’s recommendations in a thread, I bought 8 just to be sure.

Seeing yo have ordered replacement, Swap the J201 under the Tone Trimmer with Q2 to see if your voltage comes up!

 

[Chas Grant]

Seeing yo have ordered replacement, Swap the J201 under the Tone Trimmer with Q2 to see if your voltage comes up!

I agree!! Swapping parts is a very effective way of troubleshooting! Even more so when you have more on the way!

 

[DrumBuster]

I will! Thanks for the tips guys! Guess I’m falling down the rabbit hole in the diy pedal world lol

 

[DrumBuster]

I’m back guys! They arrived today, it has been a painful 2 week wait lol

 

[DrumBuster]

I’m back guys! They arrived today, it has been a painful 2 week wait lol

Swapped the faulty transistor, now I have a weird sound, is like noise. Plus when I adjust the trimmer of Q3, I hear crackles.

 

[DrumBuster]

All transistors have been biased to 5v as test, but I can’t hear my guitar at all

 

[DrumBuster]

I think I kinda damaged q3 and q2’s pads a bit, but they still read 9v

 

[DrumBuster]

The transistors have now been replaced with pf5102s, I now get that hum but no tone, just on bypass.

 

[music6000]

I think I kinda damaged q3 and q2’s pads a bit, but they still read 9v

Check Q2 & Q3 for Continuity with Matching Colours.
If you don't get continuity, It aint going to work!
You can get Voltage at the Drain, that doesn't mean the other 2 legs are working correctly: