CR-820 in protection, need help

[tonefoto]

I have a CR-820 I am trying to get back into operation. Its had its driver transistors changed out with NTEs on the left channel and has a bad 2SC1624 NPN driver on the right channel. 3 of the 6 fusible resistors have been changed with the exception of a few 4.7Ω which I will replace later. It had a pair of shorted output transistors on the right side which I've replaced. All my testing is powered through DBT at this point, its not coming out of protection.

I'm trying to figure out the pinout for the NPN and PNP drivers. I am hoping a Yamaha guru out there will help me out. I don't see any pinout markings on the board. I can't make out any on the service manuals board diagram either.

I plan on replacing both pairs of drivers with MJE15032G/MJE15033G which are BCE.

I'm confused because I read a thread on a CR-820 rebuild that showed the MJE15032Gs with crossed legs for installation. I'm not sure why that would be unless the original NPN/PNPs are not BCE pinout.

 

[tonefoto]

I have a CR-820 I am trying to get back into operation. Its had its driver transistors changed out with NTEs on the left channel and has a bad 2SC1624 NPN driver on the right channel. 3 of the 6 fusible resistors have been changed with the exception of a few 4.7Ω which I will replace later. It had a pair of shorted output transistors on the right side which I've replaced. All my testing is powered through DBT at this point, its not coming out of protection.

I'm trying to figure out the pinout for the NPN and PNP drivers. I am hoping a Yamaha guru out there will help me out. I don't see any pinout markings on the board. I can't make out any on the service manuals board diagram either.

I plan on replacing both pairs of drivers with MJE15032G/MJE15033G which are BCE.

I'm confused because I read a thread on a CR-820 rebuild that showed the MJE15032Gs with crossed legs for installation. I'm not sure why that would be unless the original NPN/PNPs are not BCE pinout.

Think I figured it out by deduction. BCE on both NPN/PNP driver pairs. Its coming out of protection with the NTEs removed from the circuit. Continue with pushing the stone up the hill on this one. One thing I'm seeing with this vintage Yamaha is you must exercise a lot of caution with heat on these board traces. They lift by just looking at them.

 

[tonefoto]

Think I figured it out by deduction. BCE on both NPN/PNP driver pairs. Its coming out of protection with the NTEs removed from the circuit. Continue with pushing the stone up the hill on this one. One thing I'm seeing with this vintage Yamaha is you must exercise a lot of caution with heat on these board traces. They lift by just looking at them.

I got it on DBT and could read bias on right side but none of left and the left is distorted, right side is ok. I guess there's something wrong in the bias circuit. Does this sound familiar? Any suggestions on where I should be looking would be appreciated.

 

[avionic]

I guess there's something wrong in the bias circuit.

First check the resistance of the output emitter resistors.. Have the outputs been replaced on the left side ?

 

[avionic]

Check R763 and 765 4.7Ω output base resistors. Also check the fusible resistor FR701 ( 68Ω/85ma )

 

[tonefoto]

Check R763 and 765 4.7Ω output base resistors. Also check the fusible resistor FR701 ( 68Ω/85ma )

Thanks Avionic for your response. I need the encouragement, this board is not the easiest to navigate. I checked all 4 fusistor 4.7Ω and they read close enough 4.8Ω. I replaced the right side outputs not the left, but the left tested good. I checked all 4 emitter resistors that reside in a group and they tested good. I replaced the 68Ω fusistor resistors.

 

[tonefoto]

Check R763 and 765 4.7Ω output base resistors. Also check the fusible resistor FR701 ( 68Ω/85ma )

I have to revisit my solder traces on the drivers for the left side (MJE15032G/MJE15033G). These traces are on the ragged edge after the first guy thrashed them.

 

[tonefoto]

I have to revisit my solder traces on the drivers for the left side (MJE15032G/MJE15033G). These traces are on the ragged edge after the first guy thrashed them.

I didn't check the two white 0.22Ω and 2 green 022Ω resistors shown here. I'll check them, along withe orange resistors.

 

[tonefoto]

I replaced the right side output transi

I didn't check the two white 0.22Ω and 2 green 022Ω resistors shown here. I'll check them, along withe orange resistors. View attachment 2221988

I replaced the right side outputs with a pair of 2SD388 / 2SB541 pulled from a Marantz 2238B. The left side (distorted side with no bias reading) has the original CR-820 outputs.

 

[tonefoto]

Check R763 and 765 4.7Ω output base resistors. Also check the fusible resistor FR701 ( 68Ω/85ma )

Thank you Avionic again for the suggestions and guidance as always its great members like you are willing to help keep these relics alive. I went over the traces on the 4.7Ω resistors on the left side and found yet another lifted trace from the work done prior to me. Its now tracking bias on the left side and distortion is gone. Going to replace all the lamps and clean her up..

 

[tonefoto]

Thank you Avionic again for the suggestions and guidance as always its great members like you are willing to help keep these relics alive. I went over the traces on the 4.7Ω resistors on the left side and found yet another lifted trace from the work done prior to me. Its now tracking bias on the left side and distortion is gone. Going to replace all the lamps and clean her up..

Where is the voltage measured for the lamps? I thought I should be looking for 12VAC. Am I incorrect? I traced the red and white wires coming from the 3 lamps to the wire wrapped pins on the main board and I'm not seeing much AC there, just 22VDC. I have no meter or dial lamps lit.

 

[avionic]

I thought I should be looking for 12VAC. Am I incorrect?

No. There wired in series parallel 22-24 VDC.

 

[tonefoto]

No. There wired in series parallel 22-24 VDC.

OK, I see that voltage, all the lamps must be shot then.