CR-2020 - Smoking Resistor

[avionic]

What voltages are you seeing around TR607?

 

[zaskarx]

All 3 legs of TR607 are ~+42v, as are those of TR608

TR606 is as follows:
B -99.3v
C +42.1v
E -99.5v

Unfortunately the copy of the schematic that I have isn't super clear and I can't tell what the voltages are supposed to be.

 

[avionic]

I can't tell what the voltages are supposed to be.

Measure the voltages on the corresponding components of the working channel will give you an idea of what they're supposed to be.
From what I can tell. They are not even in the same ballpark.

 

[avionic]

Check your ground wires marked ( E ) for continuity to ground ( chassis).On the bad channel.

 

[zaskarx]

Ok, so this is weird most of the values on the good side are close to the bad side, not seeing anything that stands out, all grounds check out fine.

Good Side

TR 611
B +42.8
C +59.3
E +42.3

TR 612
B +40.7
C -59.4
E +41.2

TR 608
B +42.8
C +40.6
E +42.2

TR 607
B +40.8
C +42.5
E +42

TR 606
B -103.1
C 40.8
E -103

 

[avionic]

Ok, so this is weird most of the values on the good side are close to the bad side, not seeing anything that stands out, all grounds check out fine.

Good Side

TR 611
B +42.8
C +59.3
E +42.3

TR 612
B +40.7
C -59.4
E +41.2

TR 608
B +42.8
C +40.6
E +42.2

TR 607
B +40.8
C +42.5
E +42

TR 606
B -103.1
C 40.8
E -103

I don't think the good side is that good either.

 

[avionic]

A little better scan.

.http://sportsbil.com/yamaha/cr-2020-s.pdf

 

[zaskarx]

Thanks Avionic, I'll poke around and see if I can figure out what's gone bad...any general advice on strategy or where to start?

 

[avionic]

Did you duplicate what you did to the " bad" channel to the other channel? As far as replacement parts? Otherwise, the common denominator is the power supply.

 

[zaskarx]

No, the only part I replaced on the "good" board was the noisy transistor...tr607 I think. The rest is stock. Wouldn't the voltages be off on the pins on the top of the board if the power supply was bad? Not second guessing you, just curious.

 

[avionic]

PS is not only B+ and B- but also ground return. With almost identical voltage issues in both channels. It has to be something common to both channels

the noisy transistor...tr607

2SC458 ? The thermal tracking bias transistor TR608. Do you still have both of the 2SC458's? Frankly I've never had any issues with the 458's in the bias circuit.

 

[avionic]

Post a close up photo of the PS board Back RH quarter around the relay.

 

[zaskarx]

Correct, I still have the original 2SC458s and will put them back in tomorrow. Pics are attached, let me know if you need any others.

 

[zaskarx]

Ok, old 2SC458s are back in, unfortunately I'm still seeing the same weird voltages I'll start checking voltages on the power supply board.

 

[avionic]

Post a close up photo of the PS board Back RH quarter around the relay.

Just wanted to see if the small black wire going to the (E) pin beside the relay was there. It connects to the Blue wires on the verticle e-cap board. When removing the power supply board this wire sometimes gets broken at the pin behind the relay.

 

[zaskarx]

Oh yeah, that did snap off and I had to replace it when I recapped the vertical board.

 

[avionic]

What position is your speaker select switch in? Disreguard...

 

[zaskarx]

Ok your instincts were correct Avionic, something is definitely funky on the PS board, measured voltages on the two heatsinked transistors on the center of the board (which I had replaced) are as follows:

TR715
B -58.02
C -.98
E -58.3

TR712 (values didn't change when I turned the receiver on)
B 0v
C -.3v
E -.3v

 

[avionic]

You have a private message.

 

[avionic]

Ok your instincts were correct Avionic, something is definitely funky on the PS board, measured voltages on the two heatsinked transistors on the center of the board (which I had replaced) are as follows:

TR715
B -58.02
C -.98
E -58.3

TR712 (values didn't change when I turned the receiver on)
B 0v
C -.3v
E -.3v

Well that would mess up the works.