2250 - Tuner stopped working

[djathens]

I had been listening to the local jazz station for several hours today at work when I thought to myself, "That's a long pause between songs...", so I walked over and noticed that the signal strength meter was reading zero. I proceeded to tune up and down the dial, in both FM and AM and got nothing, signal strength remained at zero. The Phono and Aux inputs are working fine (I have nothing plugged in to Tape 1 or 2). I ran the dial up and down a half dozen times and turned the input knob through the inputs a couple dozen times to no avail. The antenna is still firmly connected. When I am on either FM or AM and turn the volume past 12AM I can hear some hum/hiss like the output side of the amp is still working, it just seems like it is no longer receiving an input signal. I have yet to open the unit up to look at the tuner board. Any ideas? Thanks!

 

[rBuckner]

Check the +14Vdc power supply at pin J806 on the power supply board. Ground is on J803 and J805 on that board or you can just use chassis ground for your meter "-" probe. Check the +35Vdc supply on pin J804 while you're there but I suspect it's likely okay.

 

[djathens]

Check the +14Vdc power supply at pin J806 on the power supply board. Ground is on J803 and J805 on that board or you can just use chassis ground for your meter "-" probe. Check the +35Vdc supply on pin J804 while you're there but I suspect it's likely okay.

Thanks for your reply and sorry it took a while to get in there and look. I checked J806 and got no reading, I then checked J804 for sanity and got +35Vdc. How much trouble am I in?

 

[rBuckner]

Not too much! No +14V would make for dead tuners. Measure for +14.6Vdc at the cathode (striped) end of zener diode H810. If that's bad you likely need a new one although it's possible cap C806 is bad. If that's good, measure all three legs of transistor H804 and report your findings. Also, with power off, take an ohms reading from pin J806 to chassis ground and report that.

 

[djathens]

Not too much! No +14V would make for dead tuners. Measure for +14.6Vdc at the cathode (striped) end of zener diode H810. If that's bad you likely need a new one although it's possible cap C806 is bad. If that's good, measure all three legs of transistor H804 and report your findings. Also, with power off, take an ohms reading from pin J806 to chassis ground and report that.

Thanks again for the tip! I haven't had a chance to check those components yet, but oddly enough, the tuner resumed functioning this morning. That leads me to believe that there is a component that is on the verge of complete failure, and perhaps it's just having a good day today?

Is it worth it to try and check the components while the tuner is working and see if they are reporting any off-spec/fluctuating voltages?

 

[rBuckner]

Probably not. I'd suspect a cracked solder joint or a transistor that's becoming mechanically intermittent. Press lightly with a non-metal item such as a wood stick on various parts and on the board surface to see if it's something like that. "Intermittent" is a 4 letter word to a technician!!

 

[djathens]

Probably not. I'd suspect a cracked solder joint or a transistor that's becoming mechanically intermittent. Press lightly with a non-metal item such as a wood stick on various parts and on the board surface to see if it's something like that. "Intermittent" is a 4 letter word to a technician!!

The tuner stopped working again today so I'm going to gently probe around with a chopstick and see if anything reveals itself as the culprit.

 

[airtime]

Stupid question but does moving the selector have any effects on tuner sound?

 

[djathens]

Stupid question but does moving the selector have any effects on tuner sound?

No, I can cycle back and forth on the input selector, and the tune up and down the frequencies to no effect, there is no sound whatsoever. When the tuner is not working, the red STEREO lamp is not lit, even though it's tuned to a station that would normally light it up.

 

[slowpat]

No, I can cycle back and forth on the input selector, and the tune up and down the frequencies to no effect, there is no sound whatsoever. When the tuner is not working, the red STEREO lamp is not lit, even though it's tuned to a station that would normally light it up.

If you have a can of freeze spray, maybe you can try that too. Did the tuner go out after about the same amount of usage as the first time?

 

[djathens]

If you have a can of freeze spray, maybe you can try that too. Did the tuner go out after about the same amount of usage as the first time?

We were on vacation for a month, and then came back and the tuner stopped for the first time after 2 days of using it again. It didn't work for two weeks, then started working again and worked for 12 days before going out again today. What is 'freeze spray'?

 

[slowpat]

We were on vacation for a month, and then came back and the tuner stopped for the first time after 2 days of using it again. It didn't work for two weeks, then started working again and worked for 12 days before going out again today. What is 'freeze spray'?

I'm suspecting a marginal component was going out as it heats up. The spray is a can of chemical that cools the components you spray onto. I should have asked a clearer question - how long has the receiver been powered on before the tuner goes out, and if it was the same duration each time? Meaning the tuner goes out say after two hours of listening? If a component gets too hot, and you spray that component, it will come back on.

 

[djathens]

I finally had a chance to test some more components. The zener diode H810 read correctly, but when I touched the probe to one of the legs (can't remember which) of the transistor H804, the tuner came back on and stayed on for the duration of my testing. The base leg read 13Vdc, the emitter leg read 13.5Vdc, and the current leg measured 28Vdc. All of those are a little low (should be 14/14.6/34.2Vdc respectively), could the transistor start acting like an on/off switch if it's not getting enough voltage?

I very gently touched a chopstick to the various components on the board and didn't notice any obvious looseness, and the tuner did not drop out at any time.

 

[rBuckner]

I've experienced that before. The transistor is bad, likely connections from the legs to the silicon. Some old transistors had silver plated legs that tarnish black. Some have proposed that the oxidation creeps up inside and eventually makes a bad connection. Interesting but I'm not sure I buy that! At any rate that guy can be replaced nicely with an MJE15030 and the legs are in the same order. Hope that does it.

 

[dr*audio]

Before you replace the transistor, examine the solder joints on the board at the transistor. Look for a dark circle or crack around the component leads. If you see that, re-solder the solder joints on the transistor. The solder joints go bad from heat. This is much more common than intermittent transistors.

 

[rBuckner]

Still, that guy has a had a long hard life - replace it when it's convenient if resoldering doesn't fix things.