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Sir Slice4444 . . . . .
That's one fine old unit . . . .my brother in law had one that I had to repair in the past . . . . you certainly have discriminating tastes . . . .
With your found, "slowly blowing" 5 amp fuse, BLACKENED internally, indicative of a severe overloading being subjected to it,
Most suspect is either the YELLOW boxed in full wave bridge rectifier, or one or both of your potted STK power amplifier modules.
To enact a safe non damaging technique, for troubleshooting analysis:
Commandeer one of Mamma Cass's table lamps, or one of your mechanic trouble lights that use incandescent lamping.
Use a 60-100 watt lamp in it and set up beside your amp.
Initially use an ohmmeter to test the four diodes within the DO1 within the schematics YELLOW box markings.
If you don't find any shorted diodes units, within DO1, the trouble must lie within the STK power amplifier modules that are at the
end of my marked in and arrowed BLACK and RED lines from terminal 13 and 14 of the PS PCB.
Test the lamp to see that its series switch is closed and has the lamp lighting .
NOW you use two clip leads to connect the lamps plug blades to the now vacant fuse clips.
Plug in the amp to AC power and prepare to turn it on for about a one-two-three Mississippi count.
Upon turn on, you very-very likely will get a bright lighting of the test lamp, that's where a new fuse would have BLOWN, had one been put in.
A moderate to dull glow of the lamp would have been indicative of proper amp power consumption, but it would not be getting enough voltage
for normalcy .
SOOOOOOOO . . . .if the lamp was BRIGHT, either unwrap the wire on terminal 13 if a wrapped connection on a stake, or unsolder it.
Then do the same turn on test and watch the lamp, if BRIGHT, then shed the terminal 14 wire connection also.
Power up the unit and check the lamp, if no longer being BRIGHT this time, the problem is in one or both of the STK power modules in the power
amplifier section.
Loosen mounting screws unsolder 6 connections replace unit and replace 13-14 wiring and test again.
OR there are some ohm mic tests between 4 connections of a STK power module to test it . . . .I can fill in, if progressed to this stage of testing,
along with my additional posting of the schematic of the units AF power output stage.
Waiting for your feedback . . . . .
73's de Edd
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