F3 Builders Thread

[lordvader]

46 v
Using a bench supply at the moment

 

[lordvader]

I'll check those others shortly

 

[2 picoDumbs]

At this point I feel you might be having a problem with C5.

 

[2 picoDumbs]

Also measure the voltage across C5
Measure voltage across R19 too

 

[lordvader]

OK, so...

R19 8.7v
C5 37.17v

Q5 gate to drain 8.6v
Gate to source 0v

 

[lordvader]

This was after replacing c5, and r19 is fine

 

[2 picoDumbs]

Gate to drain should be 0V
Gate to Source should be 5V

 

[2 picoDumbs]

What is the voltage drop across R21?

 

[lordvader]

Just to make sure I'm measuring correctly, going from left to right :

Left is gate
Middle is drain
Right is source

 

[2 picoDumbs]

OK, so...

R19 8.7v
C5 37.17v

Q5 gate to drain 8.6v
Gate to source 0v

When C5 is charged R19 should meaure 0V
Is it possible D1 diode is installed the wrong?
If it's correct then either C5 is bad or you have a short some where.

 

[lordvader]

What is the voltage drop across R21?

0.35v across r21.
The led is not in the circuit at the moment

 

[2 picoDumbs]

Just to make sure I'm measuring correctly, going from left to right :

Left is gate
Middle is drain
Right is source View attachment 865965

Diode is installed the wrong way

 

[lordvader]

How can you be sure about the diode? This is the other channel which works fine - the silver line is in the same position.

 

[2 picoDumbs]

Not 100%

Measure resistance between grey line side of diode and gate of mosfet.

 

[2 picoDumbs]

When did you replace C5?

 

[2 picoDumbs]

Either bad C5 (or bad solder joint), incorrect Diode direction or short in that area.

 

[lordvader]

Not 100%

Measure resistance between grey line side of diode and gate of mosfet.

365 ohms

 

[2 picoDumbs]

Just to make sure I'm measuring correctly, going from left to right :

Left is gate
Middle is drain
Right is source View attachment 865965

Correct

 

[2 picoDumbs]

365 ohms

It should be at least 47k

 

[lordvader]

It should be at least 47k

Riiight... Interesting.
Would that be symptomatic of a backwards diode, or a dodgy component or joint in the area?