Yamaha R-500 problems - blowing fuses

rakeface

New Member
I acquired a non-functioning R-500. The fuse in it was blown. I replaced it and, as expected, the new one blew as soon as I turned it on.

Looking at the board, nothing looks out of place, burned up or leaky. There is one spot were it looks like there was a previous repair at the connections from the board to the speaker terminals (see photo). The two wires that were moved to the top of the board go to the negative (black) terminals. All the positive connections go to the right terminals and nothing is shorted from positive to negative, both negative connections are connected to the chassis ground.
IMG_3210.jpg .

After poking around in there a bit I have some questions:
1) All the negative speaker terminals are connected to ground - is this right? I checked on another receiver I had handy (a Sony STR D311) and on that only the A negatives go to the chassis ground, the B negatives do not.

2) From what I've read, it seems likely that the transistor pack (STK2040) is blown - is there a way to test this?

3) Any other likely culprits or things I should be / could be testing?

4) The other issue this receiver has is that the shaft for the bass control pot is broken. It is a 30K linear dual gang pot - seems to be rare as hen's teeth. Would replacing this with a 20K or 50K pot be ill advised? If so, I will probably leave it in, grind a slot in the sub of the shaft and treat it as "set it and forget it".

Thanks!
 
Back
Top Bottom