David Farber wrote:

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** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.


Next (but still without a new set of IGBT's installed) I slowly powered
the unit on with the Variac. Relay K1 now energizes right after power up
and the internal green LED glows normally. I will now place an order for
the IGBT's and NTC thermistor. Phil brought up the point, what would
cause them to blow in the first place? After much checking, I could not
find any other faults in the circuitry. I'll update you after the new
parts arrive and are installed.

** I have you have an isolation transformer or a scope that can be safety floated above earth. You need to inspect the drive waves to each IGBT.

As you Variac up, the wave should snap on staring with a very low duty cycle, then fill out to a perfectly symmetrical square wave.



I do have one other question regarding the 25A line fuse. What the heck
is that supposed to protect? If the power supply fails/shorts, the
thermistor bypass relay de-energizes and then the line voltage is sent
through the thermistor. I think the 25A fuse will win that battle and
not protect anything. The specs on the back of the amp say, 2050W into 2
ohms so I guess a large fuse is necessary however wouldn't a smaller
fuse, maybe a slo-blo type, make more sense?


** At full power with 2ohms load, the AC will be 25amps RMS.

( 2100 /120 = 17.5 with a PF of about 0.7 = 25. )

If you know the speaker being used is 4 or 8 ohms and the player does not thrash the heck out of it - then a 15amp slo-blo will do OK.


..... Phil