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PeeCeeBee V4H GB

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pistollero

pistollero

Member
Joined 2016
Work in progress..
Need to find a cheap way to match small transistors. 20210307_210435.jpg
 
R

robodo

Member
Joined 2016
Hello,
please HELP :confused:
When setting VAS biasing, I was carelessly manipulating the multimeter probe and a short time I connected the legs R25 and R39. :headbash:

It sparkled a bit and the R4 resistor burned out before I turned off the power on. Shown in the picture below.

What was destroyed? Transistor? Who? :scratch:

I'm not an expert to find a mistake. I can only measure components if I know which ones.
I hope this is a small problem and I can repair it.

Thank you for the advice. :worship:
 

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shaan

shaan

Member
Joined 2009
robodo said:
Hello,
please HELP :confused:
When setting VAS biasing, I was carelessly manipulating the multimeter probe and a short time I connected the legs R25 and R39. :headbash:

It sparkled a bit and the R4 resistor burned out before I turned off the power on. Shown in the picture below.

What was destroyed? Transistor? Who? :scratch:

I'm not an expert to find a mistake. I can only measure components if I know which ones.
I hope this is a small problem and I can repair it.

Thank you for the advice. :worship:
Click to expand...

Hi Robodo.

Check all the resistors. Replace the burnt ones.

Check all bipolars for base-emitter and base-collector voltage with multimeter in diode test mode. For Q1,3,5,7,9 black probe goes to base, for Q2,4,6,8,10 black probe goes to base. Pin 2 is base for small bipolars and pin 1 is base for Q9/Q10. If any junction shows open or short, replace that transistor. Remove jumpers before probing.
 
R

robodo

Member
Joined 2016
shaan said:
Hi Robodo.

Check all the resistors. Replace the burnt ones.

Check all bipolars for base-emitter and base-collector voltage with multimeter in diode test mode. For Q1,3,5,7,9 black probe goes to base, for Q2,4,6,8,10 black probe goes to base. Pin 2 is base for small bipolars and pin 1 is base for Q9/Q10. If any junction shows open or short, replace that transistor. Remove jumpers before probing.
Click to expand...

Hi shaan,

Thank you for your help. I measured all the resistors and replaced only the burned R4, the others were fine. Then I measured the transistors and I detected faulty Q2

First I also desoldered the Q4, Q8 and Q10 because I thought they were also defective,...
shaan said:
...for Q2,4,6,8,10 black probe goes to base
Click to expand...
...before I found out that for NPN transistors it is necessary to apply a red probe goes to base and then these transistors were already good.

So I soldered them back. I'm glad I have more of these transistors, because I destroyed the desoldered ones.
After attaching the finished board to the heatsink and connecting the power supply. Everything seems to be fine.
Tomorrow I will make setup VAS, Offset and more, I'm finishing today.

I don't like two differences. It just seems to me that the LED D6 versus D5 is a little dimmer. And resistance between the output terminal and heatsink body is 4,7 MOhm.
This does not happen with the second PCB module. I already have it installed and all setup fine.

Any advice? Thank you.

Robert
 
shaan

shaan

Member
Joined 2009
I don't like two differences. It just seems to me that the LED D6 versus D5 is a little dimmer. And resistance between the output terminal and heatsink body is 4,7 MOhm.
This does not happen with the second PCB module. I already have it installed and all setup fine.
Click to expand...

Replace the led that's dim.

If it's showing 4.7Mohm without heatsink connected to psu ground then somewhere there is a slight leakage between mosfet backs and heatsinks. Replace the insulators.
 
R

robodo

Member
Joined 2016
Hi shaan,
the resistance between ground and output is ok. I measured it with the power supply connected :headbash:

Today I tried to set the VAS, but the mV value didn't want to change, still 0mV, even though I was rotating VR1 and VR2. As the VR2 rotates, LED D6 dims to completely dark. If I turned the trimmer back to the maximum resistance, then is the light back on D6 :confused:

I'm finishing today, I won't continue until after the weekend. I should give time to my family :eek::)

Robert
 
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