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Yamaha CR-800 Pre-amp Issues??

B

bkouba

Member
Posting here also for visibility:

I recently acquired the unit with unknown functionality. After doing some testing I was able to fire it up, but it had no sound from any input.

I have a relay click on power on, lights work, and was actually able to go through and set bias and offset. I cleaned the controls and coupler switch in the back but still no sound. I finally did a test of the main amp by turning the coupler off and connecting to Main In--was able to get sound through the speakers this way. So, I'm thinking something on the pre-amp is preventing any signal from getting through. Nothing appears bad/burned, solder connections appear okay, etc.

My question is where should I even begin on that board? Is it just a systematic check of all components or does someone have some tips of notorious culprits? Am I even headed in the right direction? Haven't checked power supply but, right or wrong, I hadn't considered it as I had lights, power to the main amp, tuning meter, etc.

Any suggestions are greatly appreciated. Thank you and Happy New Year!
 
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Dirty switches is a common issue, though normally affecting one channel. You should try different inputs like AUX, TAPE,,,
Also work all switches to see if there is any change. Probably a power supply issue since both channels affected, will
try and track down service manual, need to check some voltages...
 
mbz said:
Dirty switches is a common issue, though normally affecting one channel. You should try different inputs like AUX, TAPE,,,
Also work all switches to see if there is any change. Probably a power supply issue since both channels affected, will
try and track down service manual, need to check some voltages...
Click to expand...

I cleaned all the switches and worked them...tried aux, tape, and tuner and nothing on any. The only time I got sound was by connecting my phone via cable to the main in.

I did check supply voltage to the EQ amp board and it was ~24mV DC coming off the power supply, however when I checked the wire on the eq amp board it was only only about 5mV...so something is amiss. And my power board doesn't match the SM copy I have. Wire comes from the bottom right of the board (see pics). Now that I think about it I'll have to recheck my voltage as I'm second guessing whether I mis-read it as 24mV when it displayed .024mV.
 

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Power down the unit and work the coupler switch maybe 20 times

Need to check the power to the pre stage, should be a yellow wire, +B7, probably easiest on the power/relay board (underneath?).
Measure DC voltage, black probe connected to chassis/ground. Measure at +BE also yellow if you can't find B7
upload_2020-1-1_12-56-53.png
 
Need to step out but xxmV indicates a problem maybe TR801,2,3. Back in about 1 hr, others will chime in...
 
Crap, mis-traced the wire the first time around.

I get 18mV AC from BT point on power board and about 10mV DC from BE. However, now I heard the relay starting to trip so I'm guessing I have more things getting ready to go.
 
Okay, pulled all transistors and all check out good...I'll have to wait a bit to check again since I tore a trace and had to reattach to the board. Waiting for it to dry before I resolder.
 
OK, I've got a few more minutes... Suggest a basic health check of the power supply, I will get some test points shortly...
EDIT: Suggest test/measure FR801 47 ohm fusible, amp powered off/unplugged
EDIT: What is the power supply board number NAxxxx
 
Last edited:
bkouba said:
Posting here also for visibility:
Click to expand...
It's considered bad form to post in 2 forums.
You have a posting in the yamaha forum where guys are helping you out.
Suggest you pay them some respect and not go seeking other opinions, they know what they are doing.
 
mbz said:
It's considered bad form to post in 2 forums.
You have a posting in the yamaha forum where guys are helping you out.
Suggest you pay them some respect and not go seeking other opinions, they know what they are doing.
Click to expand...

I will abandon this one and just comment in the Yamaha. Again, I didn't want to offend anyone and all feedback was in the same line so I appreciate the help very much.
 
mbz said:
It's considered bad form to post in 2 forums.
You have a posting in the yamaha forum where guys are helping you out.
Suggest you pay them some respect and not go seeking other opinions, they know what they are doing.
Click to expand...
I agree...................................
 
bkouba said:
My apologies to both of you. Not trying to seek second opinions or go behind anyone's back I just put in two places for visibility not thinking--won't happen again.
Click to expand...
OK.. Your forgiven..:biggrin:
 
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