SOLVED M800 problems..

[Idroj]

Hi, here we go again..

I finished building this PAL 800, and when I first turned it on I got some intermittent overdrive sound but only responsive when I strummed hard, if I played soft no sound... It almost sounded as if it was gated... Went back to it and now I have 0 sound when on and full normal sound on bypass.

This time I cleaned the pcb board 2 times before installing it... Maybe the problem is these J201s I bought on eBay? I also bought the presoldered ones from pedalpcb, just haven't put them together yet.. wanted to try the regular ones first.. Should I start there?

Any help would be greatly appreciated.

Thanks in advance.

 

[Idroj]

I’ve tested all 6 smd presoldered ones and all the other 6 “normal” ones.. None of them reads as JFET.. all read as npn on my little cheap transistor reader.. If I only knew how to measure the Vp and Idss ?

 

[temol]

really...? I've already gave you the links... what else do you need to perform a simple measurement? Connect the battery positive terminal to J201 Drain, negative terminal to Gate. Connect multimeter leads to Source and battery negative (or Gate). Set a muiltimter do DC voltage.
Use breadboard if you have one.

Vp




Idss

 

[Idroj]

really...? I've already gave you the links... what else do you need to perform a simple measurement? Connect the battery positive terminal to J201 Drain, negative terminal to Gate. Connect multimeter leads to Source and battery negative (or Gate). Set a muiltimter do DC voltage.
Use breadboard if you have one.

Vp

View attachment 8452


Idss
View attachment 8453

Calm it down captain! "Simple" is a subjective word. I'm starting out and get confused easily, so please change your tone. Having said that, I appreciate these graphics, thank you. I'll measure them today.

 

[Idroj]

I was finally able to get those measurements following the instructions from above:

J201s from eBay:

Idds - Vp
0.81 - 0.92
0.62 - 0.81
0.33 - 0.59
0.78 - 0.90
0.69 - 0.83
0.61 - 0.79

Presoldered J201s from Pedalpcb:

Idds - Vp
0.72 - 0.86
0.55 - 0.74
0.42 - 0.63
0.52 - 0.70
0.90 - 0.95
0.60 - 0.75

Any help would be greatly appreciated. Thank you.

 

[temol]

They're all OK, within specs. All of them should be usable here and other projects. Remember that each time you replace a jfet you should measure drain voltage and probably adjust it a little bit with a trimmer. At least in this circuit.

 

[Idroj]

They're all OK, within specs. All of them should be usable here and other projects. Remember that each time you replace a jfet you should measure drain voltage and probably adjust it a little bit with a trimmer. At least in this circuit.

Thank you!

 

[Idroj]

I appreciate the help. Knowing they are within specs "feels" a little better... I'll keep them all... In the process of measuring the Vp and Idss, I felt a couple of times the transistors getting super hot, one even smoked a little.. I think that happened when I had them backward... I think I'm going to take a break from JFETs ?