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Yamaha CR-840 Repair

mrjoemorgan

mrjoemorgan

Member
Hi all,

I might be biting off more than I can chew here but after buying three receivers and all of them no longer working, I have no other choice than trying to fix one of them than go buy another.

I have a Yamaha CR-840. When I initially bought it it didn't work and I sent it back due to the STK being fried. It was repaired and came back home with me for 6 months of warm lovely listening.

However, over Xmas, I started to play a record and all of sudden the sound went. A few days later I tried again and the sound came back after pressing a bunch of buttons but quickly died and never came back.

Now, this is embarrassing as my dad is an electrical engineer but I am totally new to fixing audio equipment so my knowledge is very limited.

So with the Yamaha, I know it has a protection mode. I can confirm that I hear a click when it powers on, so that is not the case.

Is the speaker protection circuit operating because of a blown output stage? Which would be replacing the STK, right? Or did I get that wrong?

I can see an STK on amazon but not sure if its poor Chinese quality or not: https://www.amazon.com/STK0080II-Generic-Power-Amplifier-IC/dp/B01A7FIY2S

I have heard @avionic is the Yamaha master here so might be able to offer some light.

If anyone has any advice on how I might start to diagnose and fix this unit I would be forever grateful

Thanks in advance

Joe
 
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Greetings

Do you own a multimeter? Know how to use it?

Dave
 
avionic said:
Greetings

Do you own a multimeter? Know how to use it?

Dave
Click to expand...

Hey Dave - thank you so much for getting back to me. Yes I do own one. I used it to test my speakers and do a repair on those once upon a time but would say my knowledge is very basic.

So you think STKs are okay? I have some Dust Off spray which I can use on all the parts to see if that helps.

Are there certain elements I should test with the multimeter or look for bad connections?
 
I think first order of business would be clean switches electrical contacts with Deox-it. As well as the Front panel control potentiometers. Then re-evaluate . Remove the coupler links on the rear panel and clean them then re-install.
 
avionic said:
I think first order of business would be clean switches electrical contacts with Deox-it. As well as the Front panel control potentiometers. Then re-evaluate . Remove the coupler links on the rear panel and clean them then re-install.
Click to expand...

Roger that - going to De-oxit now. What are the coupler links?

I noticed on the front panel that the low filter on/off switch doesnt work.
 
avionic said:
Have you tried speaker B ?
Click to expand...

Yep tried speakers in different A/B R/L combos

I did just take the front off and de-oxit the knobs a LOT and tried it again. I got sound for about 5 seconds, then it tripped out again. Power stayed on but the sound went. However, now when I turn it on and off, i dont get the "click"
 
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