SOLVED Pacifier transistor voltage question

eh là bas ma

Well-known member
Hello,

I've built a pacifier and I am wondering if my voltages are ok on the three transistors.


On my build I read

Q1
C = 2.6V
B = 0.647V
E = 0

Q2
C= 360mV
B= 0.5V
E= 0

Q3
C = 9.19V
B = 4.19V
E = 3.6V

Q1 & Q2 values seem strange, so I removed Q1 from the sockets, and measured voltage at the pads :

Q1 without transistor :
C= 8.22V
B = 8.22V
E = 0V

I took the pinout from this picture :

Thank you for your help.
 

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Hello,

I've built a pacifier and I am wondering if my voltages are ok on the three transistors.


On my build I read

Q1
C = 2.6V OK
B = 0.647V OK
E = 0 OK

Q2
C= 360mV too low
B= 0.5V a little low
E= 0 OK

Q3
C = 9.19V OK
B = 4.19V OK
E = 3.6V OK

Q1 & Q2 values seem strange, so I removed Q1 from the sockets, and measured voltage at the pads :

Q1 without transistor :
C= 8.22V OK
B = 8.22V OK
E = 0V OK

I took the pinout from this picture :

Thank you for your help.

Have you rechecked all of the resistors? Do you have a way to measure transistor HFE?
 
Have you rechecked all of the resistors? Do you have a way to measure transistor HFE?
Yes I do, there is a plugging location on my DMM : I read Q1 = 0309 hfe
Q2 = 0313 hfe

Q3's leg are a bit too short to fit in the DMM, but it was OK if I read you correctly.

I removed all transistors from their sockets and measured voltage at Q2's empty sockets : E = 0V
B = 8.05 V
C = 8.95 V
Pinout according to this file : https://html.alldatasheet.fr/html-pdf/50028/FAIRCHILD/2N5088/405/1/2N5088.html

I am going to reflow resistors around Q2 (R7, R8, R9) and report.

Edit: I should mention that R4 and R9 (22M) are bigger than the other resistors, and have only four colored rings (red, red, blue and yellow at the edge).
 
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Here is some pictures from the soldering area, the populated pcb and the 22M resistor, in case someone notices something I missed :
 

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I forgot to say that the first readings I posted were taken with the circuit powered and switched off.

Here are my readings at Q2 when it is switched on, and all pots set on the middle of rotation :

E = 0V
B = 260 mV (0.5V with all pots fully CW except Tone)
C =2.2 V
 
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I think Q2's hFE is too high. Try a transistor with hFE = 100 or less. Don't worry about part numbers. Any Silicon NPN will work as long as the hFE isn't too high. 2N4401, 2N2369 are likely candidates.
I placed an order for 2n4401 and 2n2369A at my local store. I should be able to give you my results by the end of next week.
Thank you for your help !
 
Hello,

I received both transistors today. here are my readings on Q2 :

2n2369a
E = 0
B = 0.623 V
C = 2.795 V

2n4401 (180 hFe)

E = 0
B = 0.561 V
C = 0.444 V

I guess I should use 2n2369a for Q2 ?
 
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