Sansui BA-3000 runs super hot when bias set correctly

[richardpp]

Here’s a thread on the the pass-throughs that might help;

AU-20000 pass-throughs; a closer look

Hi, I thought I might share some photos and basic information I've found on the emitter resistor board pass-throughs and why they can be such a cause for concern. It's not always easy to get a look at the board without a fair amount of disassembly so I hope this helps give a bit of a picture to...

audiokarma.org

 

[Tina Louise]

Here’s a thread on the the pass-throughs that might help;

AU-20000 pass-throughs; a closer look

Hi, I thought I might share some photos and basic information I've found on the emitter resistor board pass-throughs and why they can be such a cause for concern. It's not always easy to get a look at the board without a fair amount of disassembly so I hope this helps give a bit of a picture to...

audiokarma.org

That thread looks great. Thanks.

 

[richardpp]

The back heatsink is usually the left channel, otherwise the speakers will be reversed.

I've just realised this is not necessarily true. The driver board slots are marked 'left' and 'right' on F-2512 and as long as the corresponding connectors are used at 18 and 19 on F-2511 it won't matter which heatsink is used. Balance control should make this clear.

 

[Tina Louise]

I've just realised this is not necessarily true. The driver board slots are marked 'left' and 'right' on F-2512 and as long as the corresponding connectors are used at 18 and 19 on F-2511 it won't matter which heatsink is used. Balance control should make this clear.

Thanks. I should be able to get into breaking down those bricks in a couple of days.

 

[Tina Louise]

I think I'm finally good here. @richardpp has been helping me a lot through DMs. Short answer is one of the F-2497 boards had a completely corroded trace so I fixed it (and the same one on the other F-2497 with a short length of wire just because). (well actually all 3 of the traces under the red arrows in the attached image were corroded but two of them aren't used in this design of the F-2497). Visually they were fine (in the image you'll see where I scraped off the acrylic (?) covering to figure out where the break was) but had no continuity.

I also went to 4 turn Bourn trimmers instead of single turn. 3339W-1-102LF. They fit just fine and made bias adjustment much easier. Single turns are indeed very touchy which I learned by pulling out my AU-20000 so this design just seems to be that way (which I guess I didn't notice when re-building The AU-20000 over 2 years ago).

Thanks everyone else for all your help!