Yamaha CR-640: Lights up but no sound.

[markallen]

Title fits almost exactly, so I'll post here.

Was given a non-working CR-640 in nice physical condition. Plugged in to my DBT (100w bulb), and only the power light came on. Pulled the cover, and saw the 1.5A fuse (F803) in the power supply was blown - always bad news. Replaced the fuse, and pressed power, still running through DBT. No speaker relay, but now the bulb glowed brightly - not good, I assumed a bad STK. However, it didn't take long and I saw smoke rising from PS transistor 803. I quickly shut it down. This is a 2SC2320, and not hard to assume it's toast - cracked open. Read in other threads to check the diodes off F803, and D801 gives readings both directions.

I've worked on many vintage receivers, but it's been years since I've seen any in this Yamaha series. Would really appreciate any pointers on how to proceed to resurrect this nice vintage receiver! Thanks.

 

[petehall347]

i take it you mean f803 ? check everything above the 0v line shown on the schematic .
few possibilities here one being shorted c803 .
more likely another transistor shorted though . i would expect burning resistors so tr801 needs looking at first .

 

[markallen]

Thanks for responding. Decided to go ahead and at least start by replacing the bad components I'd identified. Replaced TR803 with a KSC1815. For D801, all I had was a 1N4007, overkill for this application but . . . switched it on, bulb went dark and: speaker relay clicked!. It lives! Will check and set the offset if needed. None of the dial lights work either, so that will have to be done as well.

Always gratifying when something works without lengthy problem tracing. Usually I find when there are symptoms like, it's far more involved. I'm delighted!

 

[avionic]

Good for you...

 

[avionic]

Sure beats replacing STK power packs.