Yamaha CR-820

[Rommaster]

So, my brother scored a Yamaha CR-820 yesterday at goodwill for $5 with the wood case (and a pioneer ct-f700 as well for $6). He brought it home, plugged it in, and it's not working. Led's on the face light up but no sound whatsoever on the speakers. No fuzz, no nothing on fm, am, aux, phono, anything. I checked the fuses and they're all OK. Basically, just wondering if there's any "achilles heel" of this unit that i can check before suggesting he just takes it to an electronics repair shop. I have some experience working on electronics, just not as familiar as i'm sure some of you guys are. Any suggestions?

 

[packrat]

Check for pre-main switch or jumpers - the jumpers often go missing or the switch gets flipped. (not sure if the 820 has these, but my 800 does). Also, check the DC offset at the speaker terminals (look for the sticky thread about it)...if this is way too high (several volts, not millivolts) then there is a problem.

If DC offset is OK, operate all the controls many times with the power off, then power it up (volume down!) and then try it again. Try headphones and listen for any noises or even hiss while operating the controls again - dirty contacts can cause trouble. If nothing works, try not to poke around inside. There are several threads here where someone asked advice, got some, poked around, and come back with "oh, some smoke came out when I tried this..." and one dead receiver. Much better than one dead AKer... (hope that never happens).

The AK expert on these is Merrylander. If you want it repaired right he can do it, if he's not overworked already! If the face is scratch free, IMHO these are worth repairing.

 

[joenielsen]

There are no pre-main switches or jumpers on the CR-820, so that won't be the issue.

Other than that, I wouldn't really know where to begin, other than to say good luck. I have a CR-820 myself, and I would agree that it is worth repairing. A very nice receiver when all is right.

Did you open up the unit and check fuses located on the inside?

Did you check the tape monitor switch to make sure it is off?

 

[joenielsen]

Oh, and by the way, welcome to AK!

 

[Rommaster]

Thanks, will try some of this tonight after work. Hopefully it will have a nice low DC offset and just some dirty contacts I'll post later on how this all goes.

 

[Rommaster]

There are no pre-main switches or jumpers on the CR-820, so that won't be the issue.

Other than that, I wouldn't really know where to begin, other than to say good luck. I have a CR-820 myself, and I would agree that it is worth repairing. A very nice receiver when all is right.

Did you open up the unit and check fuses located on the inside?

Did you check the tape monitor switch to make sure it is off?

yes, the fuses i checked were inside, and also i did turn then tape monitor off. (god i wish that was my problem) Though, now that i think about it, i should hook up a tape deck just to make sure the monitor switch isn't stuck broken in the on position. Hopefully it'll just be something simple like that

 

[merrylander]

First off, after you power it up do you hear the protection relay click as it operates? If that is not happening then you may have blown outputs. If the relay does operate then there is a dirty (read oxidized contacts) switch somewhere or even a dirty volume or balance control. The loudness control sometimes gets cranky as well.

Rob

 

[Rommaster]

Nope, unfortunately no relay click. And also, i checked the outputs to test for DC offset and there is literally ZERO. No matter what setting, the meter doesn't even jump. I for a moment thought the meter might be acting up or batteries might be gone, so i tested it on my other stereo and the meter is functional. So, now what? Anything else i can try?

 

[merrylander]

Unless the relay operates there will be nothing on the outputs because it is the relay that connects the transistors to the speaker jacks. Near the relay you should see some copper wire coils about 1/2" in diameter and about 1" long. Those coils are usually in parallel with a 4.7 ohm resistor, check there fro DC voltages.

Also if you are careful, you can check at the transistor sockets. There should be about 45V DC on the mounting screw (this connects to the transistor case) but only low or no DC on the other two connections.

Rob

 

[Rommaster]

OK, will check this after work today. I will respond later with what I find. Thanks so much for the help.

 

[Rommaster]

I was reading somewhere that the yamaha's sometimes include lamps in the protection circuit/muting circuit. I looked at the schematic, but the one I have is not very good quality. Are the lamps included? The LEDs on my brother's work, but the face lamps do not.

 

[Rommaster]

I tested the 4 output transistors. All of them have roughly 45 volts on the screw terminal and very low DC on the other 2 terminals of each. I assume this is good, but maybe someone can shed more light on this? Could it be the lamps after all?

 

[Yamaha B-2]

Definitely not the lamps. They are not interconnected with any other part of the circuitry. Wait for Rob (merrylander) to get back to you. He will let you know what to check next. Am wondering if the relay is getting the power to pick up? But, don't have the CR-820 schematic to see what it takes to make it do so.

BTW - The CR-820 is my favorite small Yamaha receiver. Hope you are able to get it going. Very nice.

 

[Rommaster]

Here's the original manual. The schematic is one of the last few pages.

CR-820 manual

Just in case anyone needs it. :thmbsp:

Also, Merrylander,
I see the 2 coils right near the relay (hard to miss them), but i don't see the 4.7 kohm resistor.

 

[merrylander]

Not 4.7 kohms, just 4.7 ohms, regardless it sounds like the two visible output transistors are good, unfortunately the other two are hidden by the power transformer. Still you might check between ground and the two terminal posts in the corner near the transformer. This is where you normally set the idling current, but if the two hidden transistors are sick you will get high DC here to ground. If they are good, then the probability is that the protection circuit itself is bad - I have had this on the odd 820/620.

Rob

 

[Rommaster]

Hey merrylander,

I tested tp1 to ground and tp2 to ground (the two bare wire posts sticking up near the corner by the transformer) and each gave a voltage of near 45 volts. So does this mean i simply have two blown transistors? If this is the case, where can i get replacement transistors for it? Thanks so much.

 

[merrylander]

Sounds like that channels outputs are toast. If you remove the black covers (don't take the screws all the way out, they slide up and off) then remove the two TO-3 transistors you can try a power up again. If the relay operates then the drivers (TO-220s on the main board) are likely OK, but they sometimes go with the main outputs. On the main board between the two drivers (2SA814 and 2SC1624 if memory serves) is a 68 ohm fusistor (white ceramic thing) it may be open or way off value, if so replace with a 1/2 wayy 68 ohm resistor.

Forget about "original Toshiba TO-3 outputs, they are most likely fakes. DigiKey or B&D Enterprises will sell you substitutes that are reliable.

Rob

 

[Rommaster]

Just removed the two transistors and the good old CR-820 relay clicked. plugged in a set of headphones and checked. Tried playing a cd player through it and works nicely. Looks like i'm transistor shopping now!! Just have to get the lamps and two power transistors and the 820 will play music again. Wow, god how i love this forum. Merrylander, i honestly cannot thank you enough. You saved a tired yamaha from forever being mute.

 

[merrylander]

Good, and somewhere around AK is the copy of the manual page that tells you how to set the idling current.

Rob

 

[packrat]

..... is a 68 ohm fusistor (white ceramic thing) it may be open or way off value, if so replace with a 1/2 wayy 68 ohm resistor.

Forget about "original Toshiba TO-3 outputs, they are most likely fakes. DigiKey or B&D Enterprises will sell you substitutes that are reliable.

Rob

Rob, What is a '1/2 way 68 ohm resistor'? I think the scan of the bias settings is lost, but there is a text version someplace, as I used it to set the balance and bias on my CR-800....

and when inside the CR-800 I see that it has Sanken outputs on one side, and 2 different ones (NTE and ???) on the other - it's been messed with! The driver transistors have also been changed out.... :sigh:

Should I replace both channels outputs and driver board transistors now with modern parts from DigiKey?