YAMAHA CR-620 Protection Relay Fun

[JB8]

Yamaha Squad -

Here's the story:

• CR-620 powers up with lights on, no sound, no relay click
• Replaced C816, no change
• Replaced TR809 with KSA1013, no change
• Replaced TR808 with KSC1845, now relay is clicking immediately (I'm used to waiting a couple seconds before these engage but this one now clicks simultaneously with the power button action)
• Through DBT, however, when I then go to engage some small test speakers via the "A" inputs, I get a very loud pop and the DBT lights up. I haven't fully engaged the speaker button to see what happens, wanted to check in here first to make sure I don't accidentally fry something
• Case voltages for the output transistors are at roughly 40V DC, for reference
• Cold idle for left is at 7.2 mV, right channel is at 12.7 mV, should be 8mV (+/- 2mV)

Thanks in advance for any advice you can provide. Super clean unit otherwise, and man, these CR units are such a pleasure to work on, everything is laid out so nicely.

 

[avionic]

when I then go to engage some small test speakers via the "A" inputs, I get a very loud pop and the DBT lights up.

I haven't fully engaged the speaker button

Sounds to me like the switch was fully engaged..

 

[avionic]

now relay is clicking immediately

the DBT lights up.

You have two issues..
1. protect circuit problem.
2. High DC voltage at one of the amplifier outputs.

 

[avionic]

With speakers disconnected. Check for DC voltage at each amplifier output via R811 and R812 -- Check the DC voltage at each end of these two resistors.

 

[avionic]

• Replaced TR809 with KSA1013, no change

• Replaced TR808 with KSC1845, now relay is clicking immediately

Check for solder bridging and transistor pin out.

 

[JB8]

Check for solder bridging and transistor pin out.

No solder bridging found, pinouts are correct.

With speakers disconnected. Check for DC voltage at each amplifier output via R811 and R812 -- Check the DC voltage at each end of these two resistors.

Speakers disconnected, power on, speaker switch not engaged I'm getting roughly 14V DC at one end, 17V DC at the other end, on both R811 and R812.

Thanks @avionic, I was hoping you'd assist.

 

[avionic]

TR711 and TR712 emitter voltage ? ( -39vdc)

And the emitter voltage of TR802 ? ( +29vdc )

 

[petehall347]

tr805 isnt working .. or tr809 is shorted
maybe put original transistors back as they are likely ok as relay wasnt clicking as it shouldn't be right now .

 

[avionic]

Case voltages for the output transistors are at roughly 40V DC, for reference

Plus and minus 40 VDC ?

 

[JB8]

Plus and minus 40 VDC ?

Yes, case voltages for both TR726/725 are -40 VDC, TR724/723 are 40 VDC.

Emitter Voltages:
TR711 & TR712 are both -60 VDC (should be -39.7)
TR802 is at .14 VDC (should be 29.2)

Thanks for hoping in as well, @petehall347 , the more the merrier!

Based on the voltages provided, do we feel like it's all about TR805 at this point? With over 100K combined messages between the two of you I'm certainly happy to defer to your experience and expertise.

 

[petehall347]

its not all about tr805 but it is an issue .. or maybe not .. its part of the malfunctioning protect circuit .. the other issues need fixing first .

 

[JB8]

Thanks Pete. Btw, the voltages at TR805 line up exactly with the schematic. May not be important and I haven't pulled it to check it further, but wanted to include that detail just in case.

 

[petehall347]

unless i am mistaken the relay is shown in the off position

 

[avionic]

TR802 is at .14 VDC (should be 29.2)

Check fusible resistor FR801 22Ω... Check the DC voltage on both ends of FR801.

 

[JB8]

I think you're right, seems like I read a thread that reinforced, for instance, the 0 VDC at the collector of TR809 on the schematic was "drawn depicting the protect circuit activated with the amplifier outputs shorted to ground.Thats why the collector has zero volts in the schematic." Avionic was the author.

 

[JB8]

Check fusible resistor FR801 22Ω...

21.8 Ω, measured in-circuit. Let me know if I need to pull a leg for a more accurate reading.

 

[petehall347]

I think you're right, seems like I read a thread that reinforced, for instance, the 0 VDC at the collector of TR809 on the schematic was "drawn depicting the protect circuit activated with the amplifier outputs shorted to ground.Thats why the collector has zero volts in the schematic." Avionic was the author.

tr809 possibly shorted then or open circuit caused be swapping transistors .

 

[JB8]

I may have measured it wrong, double checking plus checking the DC voltage on both ends of FR801.

 

[JB8]

My first reporting on FR801 is a mystery, not sure how I could have possibly gotten any reading since I honestly can't confirm where the part lives on the circuit board... apologies. Sounds like only the E and G versions have these (?), but it may be right in front of my face, perhaps you can direct me to where this FR should be?

 

[petehall347]

connects to tr802 collector if its there