# parentheses boost



## swanforgetter (Dec 28, 2019)

hey all, 

back again with the parentheses boost from a couple weeks ago. everything’s working but the boost - no sound, LED turns on.

BS170 voltages: 

D - 9.3 v (using a 9.6 v power supply) 
S - 0 
G - 0 

i’ve measured resistor voltages as well and this is what i’ve found: 

R32: 9.6v on one side, 9.3 on the other 
R29: 9.3v on one side, 0 on the other 
R30: 0 on both sides 
R31: 0 on both sides 

i’ve redone R29 and R31 and they’ve got the same problem as they did before - voltages haven’t changed. i’ve also checked all the values and they’re correct. thinking my next best option is to redo R30 because it seems like it might be open, but before i go any further i wanted to get some other opinions. board pics here. hope everyone’s enjoying the holidays


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## Mothman (Dec 28, 2019)

Change the bs170. There is no much else that can be broken in the boost circuit.


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## swanforgetter (Dec 28, 2019)

Mothman said:


> Change the bs170. There is no much else that can be broken in the boost circuit.


i bought 5 from tayda and none of them work, i don't think it's them unless i got unlucky with a bad batch


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## Mothman (Dec 29, 2019)

check de potentiometer with the multimeter, maybe its broken. or follow schematic with a probe, is a small circuit it won´t take so long


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## Chuck D. Bones (Dec 29, 2019)

It's not the potentiometer.  Q6's gate is at 0V, should be a few volts.  Remove Q6 and measure voltage on each side of R29.  One side should be close to 9V, other side should be close to 4.5V.  If the voltage is good, then Q6 is bad.  If you can, test the next BS170 before you install it.

I don't know if you are aware, but MOSFETs are very sensitive to static electricity and are easily damaged.  They should be stored in an anti-static bag, box or foam.  When installing them, make sure your soldering iron tip is properly grounded.  Don't work in a dry (<25% RH) environment.  Work on a conductive surface.

If one side of R29 is close to 0V, then make sure R30 is 470K and look for shorts (solder splashes) around R29, R30, C22 and Q6.


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## swanforgetter (Dec 29, 2019)

Chuck D. Bones said:


> It's not the potentiometer.  Q6's gate is at 0V, should be a few volts.  Remove Q6 and measure voltage on each side of R29.  One side should be close to 9V, other side should be close to 4.5V.  If the voltage is good, then Q6 is bad.  If you can, test the next BS170 before you install it.
> 
> I don't know if you are aware, but MOSFETs are very sensitive to static electricity and are easily damaged.  They should be stored in an anti-static bag, box or foam.  When installing them, make sure your soldering iron tip is properly grounded.  Don't work in a dry (<25% RH) environment.  Work on a conductive surface.
> 
> If one side of R29 is close to 0V, then make sure R30 is 470K and look for shorts (solder splashes) around R29, R30, C22 and Q6.



i had no idea about the mosfets! tayda shipped them to me in a normal plastic bag. i’ll find something better to keep them in. i’ve talked to someone on reddit and they’ve helped me out a little bit. we also came to the conclusion that R29 is probably grounding out to something but i can’t find any shorts anywhere and there’s no solder splash. replacing it outright also didn’t change anything. i’m perplexed - it’s funny that the simplest part of the board is giving me the most trouble lol


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## Chuck D. Bones (Dec 29, 2019)

What voltage do you get at Q6's gate pad when Q6 is removed?


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## swanforgetter (Jan 1, 2020)

Chuck D. Bones said:


> What voltage do you get at Q6's gate pad when Q6 is removed?



sorry for the late reply - i get a 0V reading at the G pad without any transistor in, the readings are the same regardless of whether or not the transistor is in the socket


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## Robert (Jan 1, 2020)

Measure the resistance of your Gate pad (with no transistor installed) to ground.

You have a short of some sort on that net.... Either on the Gate pad, or the top end of R30, R29, or C22.


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## Chuck D. Bones (Jan 1, 2020)

The only other possibility is that R29 is open.  My money is on a short, or close to it.  See my post from Dec 2.  I don't think we ever saw a photo of your board, so wrong resistor value(s) is also in the cards.


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