Yamaha CR-2020 that's seen some shoddy work. Where to start?

[da_kube]

I've been chasing this signal down on the board with all the preamps and I notice I use signal right at the point that feeds the mode switch. That seems pretty great since nearly everything is seemingly before that. Right channel is fine but left is low. The ins and out of board E, right before the mode switch, have good signal.

Right after mode is the mute circuit. When I push the mute button the right side stays strong BUT the left side gets louder. I'm wondering if that switch is bad.

Can anyone tell me if there is a way to bypass it easily or just jumper the pins to confirm? Seems easy enough but I don't understand what I'm looking at here.

 

[Nashou66]

Check the continuity of the switch first.
If high ohms just douse the switch with DeOxit, you can use a pen vice drill to open a small hole in it, spray away and exercise the switch aa zillion times.

Athanasios

 

[da_kube]

Check the continuity of the switch first.
If high ohms just douse the switch with DeOxit, you can use a pen vice drill to open a small hole in it, spray away and exercise the switch aa zillion times.

Athanasios

Thanks. After I posted I did think of that. Investigated the muting switch and it seems fine. There are two left and right wires with ground, I assume one is in and another is out. They are both weaker than the right and the resistance on the muting switch is identical on both sides.

Now I think my issue is further upstream. I do get a good signal on PreMod E and then by the input to the mode switch signal strength deteriorates. It looks like there is a bypass to PreMod E so I'll start investigating that area. I do find signal symmetry at the outs of the loudness knob, so there can't be much that remains? I'm still pretty rookie so it's possible/likely I'm missing some things.

 

[Nashou66]

Yeah , first thing I do is check continuity on all switches that pass a signal . And I exercise the switch a few times and check again as some times the issue is intermittent. So selector, speaker , mute, tape monitor, loudness , coupling etc all need to be checked and cleaned regardless.

 

[da_kube]

I think it was the filter switches but I can't be certain. I blasted those and the mute switches and exercised them quite a bit. Now I get a nice clean signal through both channels. If I'm reading the schematic right, the bypass and high and low filters all go through the same switches, so basically there are three potential outs on those switches.

If anyone understands the preamp section and can tell me more on that, I'd be curious. To me, it looks like the larger board that has all the pots and controls has those circuits and boards A-E are each preamp gain stages?

In any case, things are working again. I'm going to recap and replace the bias and output transistors on the right main amp board, which has always worked.

I'm noticing low voltages going to the clear lamps. Only ~7v when they should be 9.5v. They're also all out when the prior owner said they worked. This is a doozy of a lamp job, so I'm wondering if some wires got messed up. There were some long and needless wire extensions on these AND a lot of scotch tape trying to hold the lamps in place. No idea why anyone uses scotch tape but I've seen it more than once.

 

[cjkpkg]

Same here my lamp wiring is a mess. I just noticed that someone tried to put LED's in without any resistor network and they coupled everything on just 2 of the posts instead of wiring the 2 pairs in series using all 4 posts on the relay board.

I saw this pic in a post for a CR-820 which makes sense to me more than on the 2020 service manual.

 

[da_kube]

Same here my lamp wiring is a mess. I just noticed that someone tried to put LED's in without any resistor network and they coupled everything on just 2 of the posts instead of wiring the 2 pairs in series using all 4 posts on the relay board.

I saw this pic in a post for a CR-820 which makes sense to me more than on the 2020 service manual.

That does make a lot more sense. I heard the design of these makes LEDs difficult to get looking good and I don’t mine incandescent so I plan to go that route.

If L1 and L2 are both 9.4v do those numbers add together or is that not how this crap works?

 

[cjkpkg]

IIRC there are 2 lights wired in series so the 18V gets split in half so each bulb gets the 9V - thinking back to my Tube heater wiring projects...lol.