On Oct 14, 8:39 pm, "Bob in Phx" wrote:
wrote in message

oups.com...




snip

I did check the B+ voltage and its 12.4 or so at pin 16.
I will pull out the scope right now and see what I can find at q15.

as for the transistors, which are they (Q what???)

This is how I have been testing transistors.

"Transistor Testing procedures,
To test a transistor, you'll need your digital multi-meter (DMM)
set to the
"diode" position.
Put the black lead of your DMM on the center lead or on the metal
tab of the
transistor.
Put the red lead of your DMM on each of the two outside legs of the
transistor one at a time.
You should get a reading of .4 to .6 volts.
Any other value, and the transistor is bad and will need to be
replaced.
Most often transistors short when they go bad. This will usually
give a
reading of zero or near zero, instead of .4 or .6 volts. "

This procedure is for a Tip122.... As a general rule, would this be
how I
should be checking the three transistors your mentioned????

bob in phx.

Testing transistors with a DVM assumes you know which lead is the
base. You should see a normal silicon diode drop from base to emitter
and base to collector. At room temp this is typically .6 to .7 and
will go lower as temp goes up. The emitter to collector can vary quite
a bit as you're often seeing the other circuit compoinents but it
should never be close to 0. When in doubt, removing the transistor
from the circuit board would be most likely to succeed. A curve tracer
would be even better if you can find one.

If you don't know, on the schematic, the base terminal is the
horizontal line that intersects the vertical bar inside the circle.
The emitter lead is the diagonal line with the little arrow and the
arrow direction denotes NPN or PNP. The collector is the other
diagonal.

Q11, 12, 13, 14 are all NPN devices so you should see the diode drop
with the red lead on the base and black to emitter or collector.
Looking at the PCB foil pattern will show emitter, base and collector.
Reversing the red and black leads will read open circuit if the
transistor is off the board and might show open on the board.

If I'm not too rusty, Q12 is the RF amp, Q15 the local osc, Q13 the
mixer / IF driver and Q14 appears to be AGC.

GG