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Yamaha cr-820 stereo receiver

My receiver will turn on but no sound. All fuses checkout good. The tech manual doesn't cover this problem. One of the transistors without a heat sink gets very hot and so far the FM signal strength meter does not work either. I am not a tech but with the right info I can probably locate and fix the problem. Hmmm. Any help / guidance would be gratefully appreciated.
Vince



Yamaha cr-820 stereo receiver

Tom,

I plugged in a set of interconnects into both of the phono inputs and grounded the tip and ground rim with my finger to see if I could produce a hum. I got no hum or output from either channel. Also, as you mentioned earlier, the protect relay doesn't engage. I was incorrect as to the orientation of these transistors. It turns out to be four transistors instead of one and they are located between the transformer and the front panel. Their numbers are: 7.21, 7.22, 720 and 714. The 714 gets warm while the others get to hot to touch within the first minute or two after applying power. I hope that this can make it easier to diagnosis and once again I am very appreciative to get your time and help.

Vince

Yamaha cr-820 stereo receiver

Vince,
Sounds like major output problems
722 and 720 are drivers and while they can heat up, it shouldn't be until the unit is cranking for quite a while
721 is a drive from the other channel and should be the same temperature as 719 which is its pair. If they feel the same, that channel may be good. If different, you may have problems on both sides.

Check

726 - 2SB557 - check for short or leaky emitter to collector, emitter to base, base to collector, or open base emitter
724 - 2SD427 - check for short or leaky emitter to collector, emitter to base, base to collector, or open base emitter
722 - 2SA814 - check for short or leaky emitter to collector, emitter to base, base to collector, or open base emitter
720 - 2SC1624 - check for short or leaky emitter to collector, emitter to base, base to collector, or open base emitter

Check all other transistor the same way in the channel (704, 716, 714, 712, 708, 702, 706, 710, 718)

Check diodes for short, leaky, or open (D702, D712, D710, D708)

Check all resistors for open condition, especially large 0.47ohm emitter resistors, and small value fusable resistors near the driver circuits.

Check VR702 trim pot for open condition. They sometime burn when outputs short.

Whatever you do, don't apply full AC power to the unit until after you have replaced bad parts, and after you ran up the power to the unit using a variac (variable AC power supply).
If you don't have a variac, you can use a 60 watt incandescant bulb wired in series with the 820's power cord. (You can use an outlet and a power cord with a plug to make a test jig. Using this method will allow you to test the unit without frying the outputs if a problem still exists. The way it works is that upon power up of the unit (with the 60w bulb in series with one leg of your power cord) the bulb will come on bright, and then slowly dim until it is very low in brightness. With the volume low, and just headphones, you may actually get the protect relay to engage and produce sound. If the bulb comes on bright and stays bright, you still have a short condition, but you won't cause any further damage.

And then if you still have a problem, check the other channel for issues as well. I also think you have a PS regulator problem because of the "no FM signal" condition. And it would be advisable to check all regulator transistors, as well as D808, D809, D810, D811 because the +45 or -45 regulator could have fried because of the output problem.

But if you are not familiar with these type of repairs, you may look to find someone to do this work.

Tom

Yamaha cr-820 stereo receiver

Tom, thanks so much for your time. I think I better take your advise and find someone qualified as this seems to be way out of any expertise that I thought I may have had.
Vince

Yamaha cr-820 stereo receiver

Vince,
Good idea if you are not experienced in this type of work. Give me a call if you need any further help
Tom

Yamaha cr-820 stereo receiver

what is the tr number of the transistor that is getting hot, it should be marked on the board close to the transistor

Yamaha cr-820 stereo receiver

Vince,While no sound output could be almost anything, the fact that you don't have any signal strenght on FM points to a problem with the 12v regulator power supply. You should check to see if you get any sound or hum when you turn up the volume when in the phono position. If this is the case and providing that there aren't any blown fuses, I would look at the following:
Transistor TR809 in the regulator power supply marked 2SD400, could be bad, as well as the 12 volt zener diode D806.
If you don't have any sound in phono, and the protect relay isn't engaging a short time after turning the unit on, you may have more seriouss, or multiple problems.
Tom

Yamaha cr-820 stereo receiver

Hi Tom,

Thanks very much for getting back to me. However, my problem is not with the FM tuner section. When I turn the Receiver on I get no sound at any volume setting from any of the inputs at all. No hums, whistles or bells. As I stated the only thing that is noticeable is the smell of heat generated from a transistor that in many cases has a heat sink attached to it. Its location is coincidentally in front of the tuner section. Any additional help that you would be kind enough to provide would be very much appreciated.

Regards,

Vince