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Yamaha CR-800 Faint Channels

B

bkouba

Member
Hoping someone might have some sage thoughts on a CR-800 I've been struggling with. This unit had no sound when I got it, but I have since worked through to almost bring it back to life (with much appreciated guidance from avionic last year).

I have replaced fusibles and recapped the PB, main amp, EQ, and pre-board. I cleaned/worked coupler switch, disassembled function selector to clean, and have cleaned speaker selector.

Have great sound out of Main In, so have been focusing on areas ahead of that board. Had great sound out of R channel via aux and phono, however L channel was very faint. (Measured ~49VDC to EQ and pre boards.)

Switched original transistors on EQ board (R to L, L to R to see if they were the issue) and then got faint sound out of both channels. Replaced transistors on EQ and pre-board (ksc1845 for 2sc1345, ksc2690ays for 2sc1166) to be safe and still faint R&L channels. I even put back in the original 1166's and same result.

I've been trying to track down if I have a grounding issue, but have come up with dead ends. I don't see a solder bridge, yet, and have been able to test continuity across boards via ground. My brain is racked and feel like I'm overlooking something, but can't figure out what. I greatly appreciate any help.

Thank you!
 
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First check power supply voltages feeding the PRE board ( pre-amplifier )....
 
Find and verify fusible resistor FR502 is still 220Ω ..
 
avionic said:
First check power supply voltages feeding the PRE board ( pre-amplifier )....
Click to expand...

I'll recheck, but it had been ~48vdc to preamp.

I now have the R channel back (no clue what I did...), but L is still faint. Obviously on Mono L&R are good/equal and on High Blend I also get a louder sound out of L.
 
I have a scope and signal generator too. May need to go that route. What's the best approach? Injuect signal and compare L & R across preamp? For probe ground is chassis ok or use a ground wire on the preamp?
 
avionic said:
Sounds like you still have a dirty switch or control..
Click to expand...
I have sprayed/worked quite a bit so thought I was good...is there any way to disassemble the lever switches to be absolutely sure? Just carefully bend tabs back?

I had removed all potentiometers and sprayed into bottom slots and worked well, so the unknowns are the lever switches.
 
avionic said:
MODE switch is the likely culprit ...
Click to expand...

Ok, disassembled all lever switches, cleaned, and fired her back up...this thing won't budge, still quiet L channel, about equal when set to Mono.

Currently running 48.1vdc to preamp, and FR502 is spot on 220ohms.

Guessing it may be time to trace the signal to see what's going on. Is chassis ground ok for probes or do I need to/should I use ground on the board?

I also just noticed I'm starting to get hissing/crackling in the speakers...guessing some of the transistors on the main amp are going noisy. Outputs and 458's on the heat sink were already replaced.
 
avionic said:
Post a photo of the installed subs..
Click to expand...

KSC1815 for both. Read that 1845 would work, but 1815 may be better?

I've noticed more on R, but not sure if that's because of the quiet L channel. I do believe it may be both. It's not constant either--sometimes it's there, sometimes no. It can take a little bit to flare up. Definitely mostly R.
 

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bkouba said:
KSC1815 for both. Read that 1845 would work, but 1815 may be better?

I've noticed more on R, but not sure if that's because of the quiet L channel. I do believe it may be both. It's not constant either--sometimes it's there, sometimes no. It can take a little bit to flare up. Definitely mostly R.
Click to expand...
Looks like one is installed backwards. Curved side of the 1845/1815 should be against the heatsink.
 
avionic said:
Looks like one is installed backwards. Curved side of the 1845/1815 should be against the heatsink.
Click to expand...

Ok, I'm not sure if flipping the transistor was magic, but I now have both channels?

Only other thing I did was pull R501 to test and make sure it was 4.7k.

Still have R channel static/crackling that shows up after running for a bit. Should I be targeting the four 2sc1124's as they're on the top 10 noisy? I just happen to have four KSC2690AYS's.

If I should also just go ahead replace TR701-704 and TR709-712 here is what I have:

701-704 (2sa572): KSA992FBU (I assume the 992FBTA is the same, just tape?)
709/710 (2sc734): KSC1845/1815 (also read possibly KSC2690AYS w/complementary KSA1220AY?)
711/712 (2sa561): KSA1220AY?

If I use 1845/1815 for TR709/710 , is there a good complementary candidate for TR 711/712?

I am good on 1815's, but only have two 1845's left...and mouser/digikey were out last I checked.
 
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