follow up....
found q15 and the Fluke frequency counters shows from 998 to around 2000, as
the dial is moved up and down the scale... So, I figure that the oscillator
is working!!!!!!!
So, what to check next????????
The three transistors, I guess????? if so which ones....
bob in phx.
"Bob in Phx" wrote in message
...
wrote in message
oups.com...
Bob in Phx wrote:
Hello to all and thanks for looking.
I've been working on a used (but new to me) pioneer sx-727
receiver. When it
got to my house, the left channel was out, but a couple of shots of
solder
to the numerous wirewrap connections fixed that...
snip
A quick check of the Internet and I found the full service manual
here
http://www.hifi-museum.com/lib/misc/...-sx-727_sm.pdf
The AM alignment section states to put a 455hz signal on pin 15 of
the AM/FM
unit and tune to the upper end of the dial. I did that and got
tone!!!!(see
page 13 of the manual above) so I believe that the oscillator is
working
(right?????)
snip
So, if someone has the time to look at the schematic and can
suggest what I
should do next, or what to look at, or how to test, that would be
great. If
you can, please make the suggestions as detailed as you can, having
never
worked in this field as a professional, nor having had any
training, its
sometimes hard for me to understand the suggestions....
thanks in advance
bob in phx.
Dang, I remember working on those when it and I were new. That AM
section looks pretty straightforward. Back then power amps were the
main failure.
Have you checked the AM B+ on pin 16 AWE-015 board? If that is OK, is
the local oscillator running (Q15)? Its frequency would be carrier
+455 kHz, roughly 1MHz-2MHz as you tune end to end. Nearly any scope
could verify something that low.
The electrolytic caps are suspect at that age and might cause the AM
section to malfunction. I wouldn't expect any problems with the 3
transistors but being bipolar they can be easily checked with the
diode test of a DVM.
GG
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.