Yamaha CR-1020 Relay Issue

[Bluhn321]

Hello all,

I have a Yamaha cr-1020 that has a problem that I just can't figure out. So the main issue is that the protection replay won't click on and therefore no sound. I have replaced the relay but without success. It does power up fine and nothing blows up. Any tips on what to check next?

Thanks!

 

[clinic-audio]

Hello Bluhn321

It is the first thing to do if your relay is not actived . Do you have DC offset (or worse DC voltage ) at the output of each power output PCB between tag O and E ?
Take a look on my drawing if you don't know where to look

 

[Bluhn321]

Alright so I did find a problem. The right board had a measurement of about 5mv but the left board had almost 50v!

 

[avionic]

but the left board had almost 50v!

Most likely a shorted output transistor in that amplifier assembly.

 

[Bluhn321]

Well I checked the two output transistors and they both seem to be working fine. Just used my multimeter to check them so not sure if that would give a 100% correct conclusion.

 

[petehall347]

check the rail fuses for the bad channel . one could be blown .
f601
f602

 

[clinic-audio]

Yourv relay will not work if you have 50V DC . This is the power transistor voltage , so one should be bad (E and C in short circuit )

 

[Bluhn321]

Checked the fuses and they check out good.

Hm, well it makes sense. Just to be sure one is PNP and the other is NPN?

 

[petehall347]

yes . one NPN 2sd424 one PNP . 2sb544 have you got the schematic yet ?

 

[Bluhn321]

Alright. I have it but haven't it really looked through it yet.

 

[petehall347]

you could check the voltages on the outputs cases to see if that could be the problem .cases are collectors . base and emitter are the pins . see how they are offset . bases should be about 0.6v + or - . emitters near 0v .

 

[Bluhn321]

Yep checked it and it checks out good again. Even though they seem to be OK I'm thinking of replacing them anyways.

 

[avionic]

Alright so I did find a problem. The right board had a measurement of about 5mv but the left board had almost 50v!

Absolutely sure you were on the correct test point ? If so, then you have a issue somewhere on that amp assy. thats holding and output transistor at rail voltage.Could be anything in the front end of that amplifier including cold solder connections.

 

[Bluhn321]

I checked the two points shown in the picture.

thats holding and output transistor at rail voltage

That's what I was thinking. I'll have a look at schematic and see what could have went wrong.

 

[petehall347]

now try black meter probe on bare chassis and red on the transistor cases one by one and see what their voltages are ..noting whether positive or negative .

 

[Bluhn321]

Alright so I got that transistor 2sb544 had -50.5v DC and the other had 50.5v DC

 

[petehall347]

now see if you can get the base and emitter voltages .

 

[avionic]

↑ Yep. Thems the ones.

 

[Bluhn321]

I got -45mv DC for transistor 2sb544 and -60v DC for transistor 2sd424

 

[petehall347]

I got -45mv DC for transistor 2sb544 and -60v DC for transistor 2sd424

base or emitter ?
i did forget to say it is important to post the exact voltages . no rounding up or down .