pioneer sx-727 am tuner not working.

[Bob in Phx]

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...

The 2 phono inputs, the aux and the Mic inputs all work fine, all three of
the speaker outputs work fine, all the buttons and knobs are working and
static free. Even the FM works great. What doesn't work is the AM. The unit
has an external Ferrite rod (adjustable coil inside of it) and external AM
and ground antenna connections. But, the AM is flat dead.

So I attached my trusty Eico 324 AM RF genny to the antenna in, (with a cap
in-between), set the genny and the tuner to about 900 and swept the dial, no
400hz tone. Up or down the dial, no joy.

A quick check of the Internet and I found the full service manual here

http://www.hifi-museum.com/lib/misc/pioneer-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?????)

Took the Eico off pin 15 and put it on the antenna input and again no signal
is received. Note that when I first tried this connection, the rf genny was
set for almost no signal and then I ramped it up, in hopes that it would
make some noise, So I am fairly sure that "I" didn't blow the front end.
That is not to say that it wasn't already blown, or that I am dead wrong...

My request is that would someone be so kind as to look at the AM front end
and the AM/FM unit schematic and give me some advice as to where to start
checking. I am a self taught electronics hobbiest, who at very least knows
the hot end of the soldering iron(15 to 40 watts for circuit boards, 100
watts for the bigger stuff etc) .....

I have most of the Eico test equipement that was made in the 1950's (ie 324
signal genny, 145 signal tracer, 950b cap tester, 377 af generator, 245
vtvm, a couple of cap and resistor sub boxes and a 460 Oscope (with a
Leader 100mhz as a backup). I also have a Fluke 1805 frequency counter. This
is not to say that I fully know how to use them all (that damned 950b has be
stumped!!!), but I do take direction well!!!

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.

 

[[email protected]]

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/pioneer-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?????)

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

 

[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.

 

[Bob in Phx]

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.

 

[[email protected]]

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

 

[Lynn]

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...

The 2 phono inputs, the aux and the Mic inputs all work fine, all three of
the speaker outputs work fine, all the buttons and knobs are working and
static free. Even the FM works great. What doesn't work is the AM. The unit
has an external Ferrite rod (adjustable coil inside of it) and external AM
and ground antenna connections. But, the AM is flat dead.

So I attached my trusty Eico 324 AM RF genny to the antenna in, (with a cap
in-between), set the genny and the tuner to about 900 and swept the dial, no
400hz tone. Up or down the dial, no joy.

A quick check of the Internet and I found the full service manual here

http://www.hifi-museum.com/lib/misc/pioneer-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?????)

Took the Eico off pin 15 and put it on the antenna input and again no signal
is received. Note that when I first tried this connection, the rf genny was
set for almost no signal and then I ramped it up, in hopes that it would
make some noise, So I am fairly sure that "I" didn't blow the front end.
That is not to say that it wasn't already blown, or that I am dead wrong...

My request is that would someone be so kind as to look at the AM front end
and the AM/FM unit schematic and give me some advice as to where to start
checking. I am a self taught electronics hobbiest, who at very least knows
the hot end of the soldering iron(15 to 40 watts for circuit boards, 100
watts for the bigger stuff etc) .....

I have most of the Eico test equipement that was made in the 1950's (ie 324
signal genny, 145 signal tracer, 950b cap tester, 377 af generator, 245
vtvm, a couple of cap and resistor sub boxes and a 460 Oscope (with a
Leader 100mhz as a backup). I also have a Fluke 1805 frequency counter. This
is not to say that I fully know how to use them all (that damned 950b has be
stumped!!!), but I do take direction well!!!

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.

WHAT KIND OF FAGGOT STILL LISTENS TO AM RADIO?

 

[Bob in Phx]

WHAT KIND OF FAGGOT STILL LISTENS TO AM RADIO?

 

[[email protected]]

WHAT KIND OF FAGGOT STILL LISTENS TO AM RADIO?

That's where you can hear somebody who _doesn't_ sound like you.

GG

 

[[email protected]]

WHAT KIND OF FAGGOT STILL LISTENS TO AM RADIO?

There is also the 'fun' factor of restoring the unit to original
condition.

GG

 

[Bob in Phx]

well, as to the why I listen to am.... I have a small transmitter that I
broadcast an AM signal streamed from the internet to various radios around
the house, including my walkman, so I can mow the yard with pleasure...

So, since I am sure that you have not gotten to the level of owning your own
home, and I am sure that you still live in the masterbaitorium of you
families basement.... **** off....

back to trouble shooting for me.... and I feel better now...

 

[bg]

Bob in Phx wrote in message ...

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...

The 2 phono inputs, the aux and the Mic inputs all work fine, all three of
the speaker outputs work fine, all the buttons and knobs are working and
static free. Even the FM works great. What doesn't work is the AM. The unit
has an external Ferrite rod (adjustable coil inside of it) and external AM
and ground antenna connections. But, the AM is flat dead.

So I attached my trusty Eico 324 AM RF genny to the antenna in, (with a cap
in-between), set the genny and the tuner to about 900 and swept the dial, no
400hz tone. Up or down the dial, no joy.

A quick check of the Internet and I found the full service manual here

http://www.hifi-museum.com/lib/misc/pioneer-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?????)

Took the Eico off pin 15 and put it on the antenna input and again no signal
is received. Note that when I first tried this connection, the rf genny was
set for almost no signal and then I ramped it up, in hopes that it would
make some noise, So I am fairly sure that "I" didn't blow the front end.
That is not to say that it wasn't already blown, or that I am dead wrong...

My request is that would someone be so kind as to look at the AM front end
and the AM/FM unit schematic and give me some advice as to where to start
checking. I am a self taught electronics hobbiest, who at very least knows
the hot end of the soldering iron(15 to 40 watts for circuit boards, 100
watts for the bigger stuff etc) .....

I have most of the Eico test equipement that was made in the 1950's (ie 324
signal genny, 145 signal tracer, 950b cap tester, 377 af generator, 245
vtvm, a couple of cap and resistor sub boxes and a 460 Oscope (with a
Leader 100mhz as a backup). I also have a Fluke 1805 frequency counter. This
is not to say that I fully know how to use them all (that damned 950b has be
stumped!!!), but I do take direction well!!!

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.

A quick lesson if you need it, the oscillaltor is always tuned to 455khz
above the station you want to receive, The mixer takes the station you want
to rx , mixes it with the oscillator and then always outputs the desired
station at 455khz. that's called the intermediate frequency. So , inject
455k into the IF to see if the IF is passing signal. Use your scope to see
if the oscillator is putting out. It should be 540+455kc at the low end and
1600+455khz at the high end. If the IF and osc seem ok, then inject RF into
the antenna to rule out the RF amp section, Even though the IF and RF might
pass signal, there is the issue of gain. There should be an AGC, (automatic
gain control) that sends a DC gain control signal to the RF and IF. This
might have the gain turned way down. And no I didn't look at the schematic
yet.
bg

 

[Bob in Phx]

Well, I am still working on the old girl. I haven't had much time, but I did
poke around a little more today...

so here is the list of know things......

1. No am at all at the speakers.
2. Frequency counter on q13, shows a frequency of the tuned station +- about
455. So The oscillator and mixer appear to be working.
3. Af signal applied to pin 14 (am out to the amp) works, as the signal is
loud and clear at the speaker.
4. If I put a finger on r57, I get an am station playing from the speaker.
The station is 550 and turning the dial does not change the station. I have
no idea why this is so....
5. I went through and soldered all wirewrap connections. This removed a
little tiny bit of crackling that I could make happen in AM mode, by picking
up one end of the entire receiver. The noise was ever so slight on full
volume...
6. inspected the underside of the AM/FM board for any dry solder connections
and or any suspect looking joints (cracks etc). I found no evidence of
anything but wave soldered connections. So it would appear that this has
never been worked on. I did touch up a couple of the connections on the
underside of the wirewrap pins. This is old habit from working on pinball
circuit boards.

So WTF is the story with resistor r57 and why do I get a radio signal at
this connection. I will be checking the 4 transistors tonight, but due to
work I haven't had a chance to verify they are working.....

Thanks for all the help so far.....

Bob in phx.

 

[Bob in Phx]

ooopsss didn't say thanks for the mini lesson on signal processing with an
am super het receiver...

I have worked on old old old tube am receivers, just not on transistors and
I am also a little short on how to identify the various sections of a radio.
I know that each one is "contained", for lack of a better word, by the
transformers.... Its just identifying them that I still have trouble
with....

bob in phx

 

[William Sommerwerck]

If I put a finger on r57, I get an am station playing from the

speaker. The station is 550 and turning the dial does not
change the station. I have no idea why this is so....

550 is probably a strong local station and you're getting rectification at
that point. The fact that changing the tuning doesn't change the station
pretty much proves it. It means that there's no signal from the tuner itself
at this point.

It's nice to see someone making a systemic effort to fix the thing before
asking for help.

 

[Bob in Phx]

William,
thanks for the complement.
I am a firm believer in fix'in it myself. A classic tinker, but with a
doctors creed "first do no harm". I don't work on other folks stuff much,
just my own. I think I inherited native troubleshooting ability from my
maternal Grandfather. He was a real genius at fixing things... and the
things he fixed,,, stayed fixed. He passed away 15 years ago and I still
miss him. As opposed to my brother in law who is a classic non-handy man.
Wouldn't know the sharp end of a screwdriver. If its broke, pitch it in the
trash...... buy a new one... drives me nuts.

So back to the issue. Since this radio has a three gang AM tuner "front end"
board, I should be able to prove or disprove your/my new theory, by
injecting an rf signal somewhere between the Front end and the AM/FM board.
There is an interconnect schematic here

http://www.hifi-museum.com/lib/misc/pioneer-sx-727_sm.pdf

on page 15. Where would you suggest I try and inject signal?????

thanks in advance

bob in phx

 

[bg]

Bob in Phx wrote in message ...

ooopsss didn't say thanks for the mini lesson on signal processing with an
am super het receiver...

I have worked on old old old tube am receivers, just not on transistors and
I am also a little short on how to identify the various sections of a radio.
I know that each one is "contained", for lack of a better word, by the
transformers.... Its just identifying them that I still have trouble
with....

bob in phx

Check that RF is getting to the mixer -----
Q13 is the mixer.
Look at the base of Q13 for the generators signal. There should be some of
the oscillators signal there too, so turn the generator on and off if needed
to see if the generators signal is getting there.

Check that the oscillator is getting to the mixer ------
At the emitter of Q13 you should see 995khz which is the sum of 540Khz +
455Khz. Again, you might need to turn the generator on and off. The osc is
Q15? It is right below Q13 in the diagram 10.4

Check that the mixer has a 455khz output --------
CF4 appears to be a transformer and ceramic filter all in one. Pin 3 on the
right of CF4 is where you want to look for the 455Khz. It might be just as
easy to check at the base or collector of Q4.

Check the IF amplifier and demodulator ----
Set the generator to 455Khz modulated, and connect it to the base of Q4 thru
a small cap to block DC, you should hear something thru the speaker.

If you can verify that all three signals are present, RF, Osc and IF, then
the problem lies else where. If one of them is missing, then we are in the
right area.

While you're at it , check to see if there is any signal level on the tuning
meter.
And give the loop antenna a good look because being external like that, they
tend to get banged up or used as a carrying handle. Also hit the shaft of
the tunning capacitor with contact cleaner, dry it well.

 

[William Sommerwerck]

So back to the issue. Since this radio has a three gang AM tuner

"front end" board, I should be able to prove or disprove your/my new
theory, by injecting an rf signal somewhere between the front end
and the AM/FM board. There is an interconnect schematic here

on page 15. Where would you suggest I try and inject signal?????

I don't see the AM front end on the interconnect diagram -- only the FM
front end. The AWE-015 is designated the FM AM Unit.

If you look at the AWE-015 schematic (page 24), you'll see the AM input at
pin 18. Q11 is the RF amp (I assume), Q12 is the LO, Q13 the mixer. The IF
goes to Q4 and Q5, which feeds T5. And then the detector.

You need to signal-inject/signal-trace along this path. Did you say you had
a 'scope? A 'scope can be very useful, as even the cheapest of 'scopes can
display well past the AM band.

 

[jakdedert]

William,
thanks for the complement.
I am a firm believer in fix'in it myself. A classic tinker, but with a
doctors creed "first do no harm". I don't work on other folks stuff much,
just my own. I think I inherited native troubleshooting ability from my
maternal Grandfather. He was a real genius at fixing things... and the
things he fixed,,, stayed fixed. He passed away 15 years ago and I still
miss him. As opposed to my brother in law who is a classic non-handy man.
Wouldn't know the sharp end of a screwdriver. If its broke, pitch it in the
trash...... buy a new one... drives me nuts.

So back to the issue. Since this radio has a three gang AM tuner "front end"
board, I should be able to prove or disprove your/my new theory, by
injecting an rf signal somewhere between the Front end and the AM/FM board.
There is an interconnect schematic here

http://www.hifi-museum.com/lib/misc/pioneer-sx-727_sm.pdf

No help for your problem, but wonder if your 727 is the one which was
stolen from me in the late 70's.

Not much chance, of course, but it was my very first 'real' piece of
high fidelity equipment, bought on an Pioneer salesperson discount, and
I still miss it. If yours has a splice in the power cord (the thief
couldn't be bothered to simply unplug it)....

I hope you get it fixed. The FM was super hot for the day, and the amp
section is very sweet. I didn't listen to much AM in those days, but I
remember it worked pretty well.

jak