Yamaha CR-800 Faint Channels

[bkouba]

Crap, I only had two 992FBU's and they aren't even close. Looking at specs, the 992FBTA are very similar, but not exact...enough of a difference to exclude the FBTA?

For the others on the amp, is it worth just replacing all while I'm in there? That's a subjective question, but I at least want to take care of the ones that should be replaced. Thanks!

 

[avionic]

KSA992FBU --- F = Hfe rank 300-600
BU is just packaging code for bulk
KSA992FBTA --- FB = Hfe rank 430-600
TA packaging code for ammo tape

 

[avionic]

Looking at specs, the 992FBTA are very similar,

Only difference is Hfe rank and packaging

 

[bkouba]

You are awesome, thank you for the help! Had it playing for close to an hour, no crackling, R/L playing strong...impressive sound. I really appreciate your wisdom and helping guide me through this bear.

Just have to go through AM/FM boards and then hopefully will be good. Couple caps look tired, but other than that I'm optimistic it won't put up a fight.

 

[bkouba]

Well, I have gone and jinxed it...finished replacing transistors on main amp today and cleaned inside. Fired it up after drying and that quiet L channel is back.

I was careful cleaning and didn't even touch the preamp. I get equal/strong L/R when going through Main In, uncounted. And that same deal with the Mode switch (good sound in both on Mono). And when I set High Filter to high blend I get a louder L channel, but thin (no bass, not full like the R channel)

Probably will break into signal tracing now since I am at a loss. Just stinks 'cause it's two steps forward, one step back.

 

[bkouba]

Ok, this keeps getting stranger...I powered off to go eat. Came back and hooked up signal generator to L channel. Noticed that it wasn't faint on the speaker so checked against R and it sounded pretty close. Hooked up up aux again and now L/R work fine.

I keep going back to your hunch on the Mode switch. Am I possibly getting intermittent poor contact or is it possible that a component near that path is going bad and when Mono is engaged it bypasses? Not much near there, however, to go bad. Not sure what or how I could test unless the L goes quiet again.

 

[avionic]

I keep going back to your hunch on the Mode switch.

Try tapping on or wiggling the switch..

 

[bkouba]

No luck, yet, getting it to reproduce. I tapped around all the solder pads, top side, components near there and L didn't go quiet.

Flipped the lever several times too just to be sure. I'll keep tapping around to see if it shows up. If/when it goes quiet again I'll get the scope on it right away to hopefully pinpoint.

 

[bkouba]

Try tapping on or wiggling the switch..

Ok, for posterity and in case anyone else comes across this post...

I had buttoned it back up since it was working. I wanted to play it for a bit but the tuner wasn't working well at all and L phono wasn't as loud.

So, opened it back up and the weak L channel came back but this time it stuck. Got the sig gen and scope out to trace. Thought it was the Mode switch or maybe a failing R501...both tested low compare to R, but I went and checked function board just to be sure I was good. Equal wave coming into and off of Function switch so followed up to Tape switch. L was good coming into the first jumper (J928) wire but gone after the first section of trace (J926). Tested continuity and the trace was broken (it was hidden this whole time below the stupid solder bead). Soldered in a short jumper to replace that section of trace and L channel is back! See circled schematic for where the trace broke clean.

Glad I found it since I was about ready to pull my hair out. Now to see if I can the tuner to actually tune with working meters.