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RX-770 Remote control issue. Works briefly after cycling receiver power.

R

RS-MN

Active Member
I have a Yamaha RX-770 Receiver. The remote (VP59250) works perfectly - but only briefly for a minute or two and then stops working until I unplug the receiver, wait several minutes and plug it back in. Then it works again for a minute or two again.

A RX-550 remote (VK38000) also works with this receiver but shows the same behavior - also works briefly after plugging the receiver in and then doesn't work until I cycle the receiver's power.
Powering down via the power button doesn't have the same effect. Only unplugging it works.

Where should I look to figure out the issue? I'd love to have the remote work all the time. Seems like something on the Receiver side, but the receiver has no other issues that I can tell. Like my other Yamaha RX receivers (RX-550, RX-596), it's had the display bulb replaced and the idle current set. No other servicing.

The Remote Control is like new; batteries are new and battery Voltage's confirmed. I've also confirmed that it the remote IR is working with the cell phone camera.

When the remote control is working, all the buttons and powered knobs work as they should.

Any help would be greatly appreciated.
 
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This may not be an issue but please check C384 shown below to make sure it’s not damaged:
B03B0165-2267-47AC-BE2A-F527558EB514.png

Also, please check the solder joints and any connections to the remote control receiver shown below. This may not be all of it but it’s a start:

BAD4405C-71EA-40EA-9562-3066A08AFE50.jpeg
 
Sparkplug said:
This may not be an issue but please check C384 shown below to make sure it’s not damaged:
Click to expand...
Thanks! It was worth a shot. I pulled the capacitor, and it measured about 4100 (a bit low, but still within 20% +/_ tol spec.) Tested fine (not jumping around, etc.) No change in remote behavior - works for a bit and then quits.
Sparkplug said:
Also, please check the solder joints and any connections to the remote control receiver shown below. This may not be all of it but it’s a start:
Click to expand...
Those look good. That is a small connector board on the rear panel for an external remote of some sort.

I've also re-flowed the 3 pins on U301 (IR receiver) and will try to scope it tomorrow. Pin Voltages at U301 are to spec and don't show any change if the remote is working or not.
 
avionic said:
Is the micro-processors memory super/ultra cap.
Click to expand...
Short answer, no. It’s not specified as a super cap.

At first that’s what I thought but I’m not so sure in this case. 4700uF isn’t high enough for that. It’s high enough to cover only very short disruptions in the 4.8V supply (maybe). Or it could be there to really clean the u-processor supply from all higher frequency garbage, there’s a 0.1uF cap in parallel with too C383.
 
RS-MN said:
Thanks! It was worth a shot. I pulled the capacitor, and it measured about 4100 (a bit low, but still within 20% +/_ tol spec.) Tested fine (not jumping around, etc.) No change in remote behavior - works for a bit and then quits.

Those look good. That is a small connector board on the rear panel for an external remote of some sort.

I've also re-flowed the 3 pins on U301 (IR receiver) and will try to scope it tomorrow. Pin Voltages at U301 are to spec and don't show any change if the remote is working or not.
Click to expand...
You may want to monitor pin17 (REM) of the μ-processor on the scope to see what happens to it when the remote stops working. See below:
FFCE9F46-1CD5-4FBC-884F-5BA5AAE68EC8.png
 
Following that pin17 trace, will br you to this set of animals (U301 plus the LEDs) that I think are related to the rem. Control functionality. See below. Check them out for proper functionality and solder work. Maybe, maybe one of the diodes could be on its last leg, don’t know for sure. :dunno:


93C6877F-26F3-458A-8AE6-531B5ECE261B.png
 
Sparkplug said:
Short answer, no. It’s not specified as a super cap.

At first that’s what I thought but I’m not so sure in this case.
Click to expand...
Yes it is.

4.7mF @ 5.5vdc and it is likely a yellowish colored cap.
 
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avionic said:
Yamaha engineering would likely disagree. :biggrin:

5.5volts is a dead giveaway.
Click to expand...
LOL … 5.5 is a definitive sign, yes, that was my first thought but the value threw me. These caps are usually a lot higher in value. Who knows, maybe with newer ICs, the didn’t need to be. :dunno:Either way the OP says the value measures right.

@RS-MN , can you provide a clear picture of this cap? Need to be sure what we’re dealing with. Thanks.
 
avionic said:
Yes it is.

4.7mF @ 5.5vdc and it is likely a yellowish colored cap.
Click to expand...
It's a black Nichicon Cap. The tall one in the photo.

U301 is a hard to take a picture of without taking the front all apart. I can get to the pins and have soldered a lead to the middle pin in anticipation of scoping it. Manual shows it is a Sharp GP1U501X component. I'll touch up the soldering after we scope it. Voltages on U301's pins measure to spec. No change to voltages when the remote is briefly working or not.
 

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  • 4.7mf cap - RX-770.jpg
    4.7mf cap - RX-770.jpg
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  • U301 - RX-770.jpg
    U301 - RX-770.jpg
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Sparkplug said:
At least at Mouser, there are no super caps of 4700uF value at 5.5V. The closest I found was a 10000uF/5.5V, I’d put it in and be done with it.
Click to expand...
Unless -- You bought the last 8 Nichicon pieces from Mouser when they went EOL about 10 years ago. :biggrin:
Got them when I was on a run of CX pre-amp rebuilds.
They are identical to the one in his photo.

That Kermet would be a good substitute. Extended memory.:thumbsup:
 
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