yes those 2SA, 2SC devices are the output transistors, the black Ics you
referred to, are something else.

What is getting hot? the main alloy heatsink? back to my orig post, can you
identify where the heat is coming from?

the source you quote does have some relation to your fault, but excessive
current isn't the only way to 'open the relay', a DC offset on the output
due to a failed o/p transistor will do the same.

I still advise against having a go yourself, but 2 o/ps are for left
channel, the other 2 for the right. its likely only 1 channel is duff.
Normally we would replace the 2 from 1 channel as a pair sine you can't tell
whether one may be weakened by the other failing.
as a test you may try carefully and without shorting any 2 metal points
together, using a voltmeter with the black wire to metal sub
chassis/heatsink, see if you can measure a high voltage, say +50v or -50v on
the middle of the 3 legs of the rectangular white ceramic resistor pack with
the red probe. Set the meter to above 50 volts DC range- ideally a digital
meter. the resistors are1 inch wide 1/4" thck, 3/4" high with 0.22 ohms
(omega symbol) on them

if you can't measure and voltage on either then your fault is probably
elsewhere, but I suspect you will measure a high (rail) voltage

Once again, if you don't know what you're doing don't try it, theres some
high voltages knocking around and its easy to short together 2 metal
contacts and make yourself a nice smoke generator.

As someone put it the other day, all the magic blue smoke is released
from the transistors!

good luck
AW