Vintage R900 Shuts Down When Hot

SomeGeoffGuy

Active Member
So I fixed the volume pot that was giving me all the trouble and de-oxy'ed all the front panel switches. When I turn it off and back on it has the standard 3 second or so delay then it clicks on - so far so good! I listened to it for about an hour today, and then it suddenly clicked off. I could get it to come back on by clicking the pre/main switch. It would play for about 10 seconds after I cycled the switch then it would cut back off. After it cuts off, when I cycle the pre/main button it comes on immediately (then back off after a few seconds). It seems like there might be a quiet click when it shuts off but not back on. It was hard to tell and I didn't want to keep messing with it and risk damaging it.

It seems like it is overheating. Is this an issue when these get older? Just looking for someone who may have had a similar problem. I am concerned about starting a diagnosis on this from scratch. Hoping for someone to point me in the right direction. I can handle a little bit of part replacement on the board. I am not sure I can find a bad component from scratch though.

I have owned the unit since about 1987. It had the power supply replaced professionally in the early 90's. It hasn't been played much since then but had been trouble free until the volume pot problem. I really want to keep this but don't want to turn it into a money pit either.

Thank you. (I will post a pic too as long as nobody makes fun of me for not having the selector dials. I lost those back in the 90's when they wouldn't stay tight).

-Geoff
 
OK
Problem is not coming from temp , it is coming from one IC ( I think STK 1070 II ) . If you have only one channel with DC offset the speaker relay will be desactivate and no more sound at the output .
The best way to act is to watch the DC offset on each channel on IC STK1070II between pin 3 or 4 (they are connected together) and ground . You schould find zero volt .
Once you see which channel is causing the trouble , you have to find a brand new one IC (beware to the fake components) and problem will disapear
 
Wow, Thank you! That sounds like something I can actually handle! Any suggestions on where to get the replacement part from?

-Geoff
 
My R-700 did this. One channel did have high DC offset, but by yamaha's spec, anything under 100mv was acceptable, and there was no trim for DC offset adjustment.

So I pulled the knobs off it and threw it in the garbage.
 
in my R900 service manual there is a procedure for power supply voltage adjustment. you can get an NOS STK 1070II from these guys, they have 2 or 3 left.http://redirect.viglink.com/?format=go&jsonp=vglnk_154644483012513&key=07a80c4f38638b813a524ba59326ca4a&libId=jqfdbffj0102ko3q000DAbr6el7er&loc=http://audiokarma.org/forums/index.php?threads/yamaha-r-900.688948/&v=1&out=http://www.sphere.bc.ca/test/semis.html&ref=https://www.google.com/&title=Yamaha R-900 | Audiokarma Home Audio Stereo Discussion Forums&txt=http://www.sphere.bc.ca/test/semis.html

you can pm me for a low resolution PDF of the service manual. I think high a res version is also available, but it may cost a small membership fee.
 
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Just a followup. I finally got a chance to open this up and take a look. Where the inner of the two STK units hit the board, the board looked pretty rough - it was browned and not quite clean looking anymore. It looked like there might have been some cracked solders. Also, there was a tiny little cap mounted to the body of the board that was jumped to the STK that was broken loose. I went through and re-flowed all the STK solders, and added a little where needed, and re-connect the tiny cap. Been playing great for hours and hours and it doesn't seem to be getting as hot anymore. Hopefully it was just a cracked solder or two. Whatever it was, it is working fine now .Had it on for hours with no issues.

Thanks to everyone for the heads up on the STK units. Whatever going on was definitely right there, and luckily I didn't need to replace anything.

-Geoff
 
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