wrote:


"* A better description is that the class B output stage includes signal tracking supplies for each rail employing switching, buck regulators. "

The way I see it, the main thing it accomplishes is to get the filter
out of the output line.



** But it is not a class D amp in any case, just a basic class B design with a a pair of "helpers" to eliminate most of the heat.



What kind of frequency does that thing actually switch at ?


** About 200kHz, the pos and neg versions are not very symmetrical.

You can see some residual riding on the output sine wave, along with minor crossover notches cos the output pair run zero bias.

BTW You need a decent analogue scope to see any of this, forget using any recent, low cost DSOs with LCD screens which totally blur detail.


Were your bad connections on the outputs themselves or the regulators ?


** It was ALL the devices on the heatsink - including a pair of 1amp, 15V regulators.



By the way, do you use unleaded solder on repairs ? I don't.


** I have some 99% tin solder - but never use it. The stuff is just awful.


Another question - you said you had to unscrew all the transistors,
was there no way to remove the heatsink with the board attached ?
Or did they make it so you can't do that ?


** The power amp module was easy enough to get out and then you access the underside of the PCB by unbolting all the power devices. A common enough assembly method these days and one Yamaha uses in a few models.

I was just trying to avoid doing that until I was sure there was a fault to be found there. It was amazing that with so many cracked joints, the PCB did NOT respond to hard impacts.


..... Phil