Sir Mafioso . . . . . . .( Now do Finns even have mafioso . . . or are you an Italian import ? )
INITIAL OBSERVATIONS:
On the left half of the schematic you have two separate PWM switching supplies and the related two toroidal transformers of each.
Then a couple of secondary windings and their rectifiers with filters that relate to acquiring minor low voltage .supplies of +12.....+5.....+15.....-15.
BUT then there are THE two MAJOR HV windings that supply the PRINCIPAL higher voltage for the POWER amp FETS, over on the other right half of the schematic.
Those two side by side power unit stages are processing the PWM digital audio coming from the IC201 as its class D output.
And it never is being analog audio until it reaches all of the way down the FET power amplifying stages to the R256+C209+C210+L206+C211+L208+R274+C217 filtering and shaping networks networks, and they will have removed all of the digital info and just leaving power analog audio output.( The SAME holds true, for the other channel to the right with its set of R226+C209+L203 .etc . .etc. )
Which finally gets bridged together by the RY201 and RY201 relays at the bottom of the schematic to then connect into the speaker(s).
Both of those HV supplys rectified and filtered outputs are tied in parallel to get the +RAIL and -RAIL HV supplies . . . as are being referenced to common ground.
They are marked at the bottom of the left hand of the schematic RAIL + RAIL-.
They would be the voltages I would check out, with their power supply filters spec'd at 160VDC. seems like ~125VDC positive and negative might be those units output voltages.
NOW . . . since you found a bad? cracked open? dead shorted ? Q219 . . . . that is being ONLY 1 of the set of 3 FQA38N30 power units that are ALL being tied in parallel . . . Q220 and Q221 are its companions.
How about doing an ohmming out of Q219 again to see how your present set of 3 read now . . . and thats using BOTH possible test leads.polarities in the OHMS testing.
THEN you shift over to Q213 and its Q214 and 215 companions and do the same test and compare, as its the SAME circuitry, except its working with a positive supply swing , while your other was working with a negative supply swing.
Do they test out the same ?
If any question still in your mind, move over to the other side of the amp where you have a whole CARBON copy circuit, using Q207+Q208+Q209 for the negative buss swing and Q201+Q202+Q203 and OHM out hose sets, as I certainly believe that you will have yourself a GOLD STANDARD, pristine reference on that whole power section, with no faults in it.
My first test procedure would be to evaluate both the RAIL+ and RAIL - supply outputs in a very fast testing.
Pull out your probes and their scope grounding is going to the amps common ground.
Pull up ye olde tyme TEK silly-scope and set hoz time base to 500ms and auto triggering mode.
Figuring that 150VDC should be our max power display, take one Vertical channel and set its mode to DC coupling and set the trace to mid scale vertically . . . . .4th scale graticule up on a scale of 8 . . . so that center is Zero VDC and vert DC voltage range such that 150 volts doesn't go off upper scale, which looks like 50VDC per division should accomplish that.
Then work with the other vertical channel in setting it up the same identical way.
Now when you clip the first Vert channels probe to the RAIL + test point AND
the other vertical channel to the RAIL- test point.
You will then be set up to simultaneously observe the power supplies power up characteristics.
EXPECTING . . . .
At initial power up . . . the scope trace is triggered and you would hopefully see the slope of the RAIL+ rising upwards until a final leveling off up at about +125? VDC.
While simultaneously the other channel will show a lowering of its trace down to a final leveling off up at about -125? VDC..
You just want to hold the duration of this test just long enough to see if both supplies display the same before that critical threshold that you mentioned before starts setting in and you have to turn the units power off.
If that 5 seconds to sweep across the screen is too slow, speed up the hoz sweep time base 1 click faster.
The next test would be the supplies ripple factors, in that situation you move the second channels baseline 0 VDC referencing down to the bottom graticle while leaving the first channel where it initially was, at mid screen.
Then switch vertical to AC coupling and initially try at 5VAC vertical sensitivity. Adjust according to ripple being found.
Now this time, when you power up, you can see the ripple response present on both supplies being dislayed simultaneously.
Expecting a like response on both channels, unless you still have problems related to loading on that RAIL- that you had the bad FET tied into.
Thassssit . . . . .
73's de Edd
