Yamaha CR-1000 Phono Stage Issue

kidcoma

New Member
I've recently recapped a Yamaha CR-1000, and it has an intermittent issue with the phono stage that is driving me a little crazy. The left channel will randomly get a sudden burst in volume, and it will usually stay like that for a minute or so before returning to the correct volume. It is very intermittent - it happens about once every 4 hours. I thought it might be a bad transistor, but the issue was still there (on the same channel) after swapping all the transistors from one channel to another. I also thought it might be a faulty trim pot, but the issue was still there after installing new. I also resoldered all the contacts on the board. The revision of the board is a little different than the schematic that is floating around on the internet, but it's similar enough that it may be able to provide some insight. Any ideas? Has anyone experienced a similar issue (yamaha or not)?

FYI the issue was there before the recap.

Thanks
 
Are you sure you're not actually getting the correct volume when it gets louder? That would make the fault a lot less weird. :)
 
It is definitely much louder than the other channel - but I could see that it might be possible that the full voltage is not reaching the trim pot to begin with. When I get a chance I'll take some voltage measurements.
 
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