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Toshiba SA-725 lost FM output

I have this receiver now from the OP. The FM stereo light does not light, and there is very little sound. You can hear some sound from some places on the dial that appears to be radio broadcast, but it is very low and unclear. The tuning meter and signal strength meter seem to be working OK, as you tune the radio, they seem to move appropriately for known stations in the area.
Tested diodes D102, D103, D104, D105, D108, I have taken readings on Q103 and Q201 and attached them as a file. OP changed out Q201. I'm wondering if replacing Q103 could be the solution.
Thanks for any suggestions.
 

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One more symptom that may help diagnose the problem. The FM muting button seems to have NO effect on the noise level.
 
Was just noticing, the complaint is no FM. IC Q201 was replaced, but that is the stereo decoder chip, not the FM subsystem/detector. Really need to start looking at Q103. Writing is getting ahead of reading. I see you made some measurements of Q103......

Almost looks like the chip is internally muted (Pin 10). This might be caused by the quad coil being grossly out of tune. You are showing 7.5 volts on pin 15 and it should be at the same voltage as pin 12 (5.63 volts). This is a manually tuned unit, so the quad coil is usually tuned with no input signal. (that agrees with the manual tuning instructions) Connect your voltmeter between Q103 pins 12 & 15, and with no input signal (tuned to a dead spot on the dial, no antenna connected) adjust T101 for a zero volt reading on the meter.
 
Thank you for your help! I adjusted T101 as you said, and now I can tune just to the right or left of a radio signal and actually make out music, though it is quite distorted and too low in volume. The sound goes away as you dial to the center of the station signal. I have ordered a HA11211 chip from Bdent.com.
The voltage on pin 9 is now 3.85V, which is closer to the spec value of 0.6V, and pin 10 now reads 3.2V, which is closer to the spec value of 5.4.
Are there any more adjustments that might help?
I have ordered a HA11211 chip from Bdent.com.
 
Pin 12 is now close to the same as pin 15 (5.63 volts)? How much did you need to adjust T101?
Replacing the chip is probably the next logical step.
 
Pin 12 and 15 are both about 5.6 with no FM signal tuned in and the antenna removed. When you dial the tuner to a station, the voltage on pin 15 goes up to about 6.3V when centered on the station, and up to about 7.5 when tuned to the "sides" of the station.
I believe it took about 2 complete rotations of the orange T101 adjustment to get the voltages the same.
The service manual says you can adjust IFT 1 to reduce distortion, but I cannot see IFT 1 on the board, the parts list, or on the circuit board drawing. It is on the schematic. Any Idea what IFT 1 is and what it might be called on the drawing? And even if I can find it, should I even try adjusting it????
Thanks!
 
IFT1 is the first IF transformer on the output of the front end. I would not suggest you adjust it.
Annotation 2020-06-15 123409.png

Pin 15 should be at 5.6 volts When the signal is centered in the passband. So when you are tuned to the center of a station, the voltage should be 5.6 volts. When tuned to one side of the signal the voltage should go up, and when tuned to the other side of the signal, the voltage should go down. Could be something internal to Q103 or, if replacing it doesn't help, may be an issue with T101 - in particular the internal capacitor.

After replacing the HA11211, you will likely have to reset the tuning of T101. With no input signal (noise only) the tuning meter should be centered.
 
Ylli said:
in 15 should be at 5.6 volts When the signal is centered in the passband. So when you are tuned to the center of a station, the voltage should be 5.6 volts. When tuned to one side of the signal the voltage should go up, and when tuned to the other side of the signal, the voltage should go down.
Click to expand...
That is what is happening. I misspoke above.

Binkman said:
aside I guess: https://forum.allaboutcircuits.com/threads/tuning-ift-of-vintage-radio-receiver-how-to.126953/
Click to expand...
Thanks for the link!
 
I thought about the front end and the one discrete IF amplifier, (and it is possible the problem *is* out there), but I believe it was said the signal strength meter appeared to be working as it should. That would mean good signal up through about half way through Q301.
 
Received the HA11211 IC today and just installed it. I adjusted T101 so pins 12 and 15 read the same voltage (5,55 V). The FM sounds clear and clean. The only issue now is the stereo light doesn't light when I dial in a station. The light will come on on various places of the dial when the receiver is NOT tuned to a station. Maybe this is just an adjustment???
 
Quite possible an adjustment of the demux free running frequency. Locate R222 - near pin 15 of IC Q201. When tuned to a known stereo station, adjust it all the way CCW, then adjust it CW until the Stereo light just comes on. Note it's position. Now turn it all the way CW, then adjust it CCW until the stereo light just comes on. Note it's position. Reposition the adjustment half way in between these two points.
 
Ylli said:
Quite possible an adjustment of the demux free running frequency. Locate R222 - near pin 15 of IC Q201. When tuned to a known stereo station, adjust it all the way CCW, then adjust it CW until the Stereo light just comes on. Note it's position. Now turn it all the way CW, then adjust it CCW until the stereo light just comes on. Note it's position. Reposition the adjustment half way in between these two points.
Click to expand...

You have been very helpful, YIIi. I have one last question for you:

The tuning dial indicator is on "93.0" when tuned to station 92.9, and just above 107.0 when tuned to station 106.9. I believe the adjustment to make them correct is TC03 according to the service manual. I cannot find TC03 by looking at the circuit board or the "Electrical Parts Location" drawing. Am I correct in the adjustment to make (and if so, is TC03 called something else), and is it worth it to adjust for this little offset?
 
TC03 is indeed the correct component to adjust, position shown in the attached.
Annotation 2020-06-18 104823.png
Tune to that station on 106.9, then tune slightly lower (but not off the station) and adjust TC03 to recenter the tuning meter. The adjustment is likely to be touchy and only a few degrees of rotation will be needed. Then tune a bit lower and again adjust TC03 to recenter the tuning meter. Chase it down until it is where you want it. Making the adjustment at the high end (where the cap has the most effect) should also bring the 92.9 station back to where it belongs. Getting perfect registration across the whole dial can be a exercise in futility, but you should be able to make some improvement.
 
DD80E233-FAA6-4F8E-8265-C9EA96CEA131.jpeg This is pretty close. All that’s left is to put in new dial lamps (when they arrive). Thanks again to everyone that contributed to this thread.
 
I just picked a 725 and am having a similar problem as the OP; no AM or FM. I've been looking at the service manual and I just can't find my problem. Aux and tape work fine.

- Fuses are good
- Cleaned S401
- Took measurements all along Q101, 102, 103 and Q201. NOTHING!

I feel like I'm missing something obvious. Is there something 'upstream' that I should check?
 
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