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bad transistor?

Started by Kristopher, July 05, 2019, 07:17:15 PM

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Kristopher

Hello All,
I am building a General Guitar Gadgets EA Tremolo. But I may have a bad Transistor.
I have audio probed along the signal path. It sounds fine through the first group of resistors and caps. But after the signal runs into the Base of Q1, it turns into a faint whine/hiss on the Collector of Q1. Has it gone bad?
Has anyone experienced a new transistor not working? Is it common for them to crap out brand new?

Here's a link to the schematic:
http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf
Thank you.

GibsonGM

What are your voltage readings on that transistor?   Did it work before?   Are you sure there are no solder bridges around it, and that there is nothing "odd" going on around the transistor's collector?  Something downstream could load it down badly (bad pot?)...check the resistor values all around it! 

It is not common that a new BJT is dead, but over-heating during installation can do it...voltages please...
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Kristopher

the voltage readings are:
C 9.3
B 0.24
E 0.0

the GGG site says Q1 should be:
C 6
B 1.4
E 0.8

Kristopher

For what it's worth, the voltage readings on the other Transistors are correct for Q2 and Q3
Q4 is slightly different
mine:
G 4.44
S 5.78
D 9.3

GGG site
G 4.1
S 5
D 8.8

PRR

Bad transistors are super-rare. (They are used by the billions in industry; a significant defect rate would cripple production.)

It is very very difficult to ruin a Silicon transistor with solder heat. (I've seen them working so hot the solder on their feet was liquid, and still doing a job.)

It is far more likely that R2 R3 are wrong value or not really connected. Maybe R2 not really joined at both ends? Maybe R3 is 15k instead of 150k?
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Rob Strand

QuoteMaybe R3 is 15k instead of 150k?
Seems very likely.

When I calculated the base voltage with 15k it worked out to be 0.23V. Very close to the measured 0.25V.

Third band orange = 15k.
Third band yellow = 150k.
Send:     . .- .-. - .... / - --- / --. --- .-. -
According to the water analogy of electricity, transistor leakage is caused by holes.

Kristopher

Yup!
That was it. R3.
I had my oranges and reds confused. 

Thank you for the assistance.