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R_J · 07-07-2025, 06:24 PM

I don't know which igbt you have, you would need to remove it to see the number, but this Sanken one should be close to show you what is internal
If the current resistor is blown open, one of the internal igbt will be bad and I would check what motor it drives is not also damaged

This whole board can be ordered from ali exp, might be cheaper than repairing as these igbt's are not cheap by themselves....

R_J · 07-06-2025, 11:14 AM

There are two (2) power supplies, for this unit, one to take line voltage down to 12v and the one on board that takes the 12v and converts it to the other +/- voltages....

R_J · 07-05-2025, 05:18 PM

You can try scoping the output of the transformer, before the diodes and see what the signal looks like, is it a smooth sinewave or does it look chopped up etc.

R_J · 07-03-2025, 04:39 PM

If C18 is bad, as in open, the top248 will start and shut down repeatedly, this cap is meant to maintain the ic's vcc voltage, D7 is a tvs diode and might check open circuit, D5 should check as a regular diode, remove one end of these diodes to check them out of circuit, if one is shorted it could cause this problem as the primary of the transformer is not being switched
D4 might be the problem as it should not check 1.5 in reverse, remove one end and check it again. D3 should check the same as D4 (obviously D4 is installed for negative voltage)
The clicking sound is usually caused...

R_J · 07-03-2025, 01:36 PM

A cap that can cause problems is C18 (4.7µf/50v) check that there are no shorts across any of the outputs

R_J · 07-03-2025, 12:39 PM

Here is the datasheet for silergy SY8388B3 with top mark R9xyz...

R_J · 07-02-2025, 04:01 PM

I was looking at the wrong power supply schematic, If the noise is coming from T1301, then it might be C1324, which is the vcc supply for the ic that drives Q1302 and the transformer. sometimes if that cap is weak the drive to the Q1301 transistor can be off and not smooth causing the transformer to make noise, or it could just be the windings in the transformer vibrating.
Here is the service manual if you don't have it, looks like they do not include the power supply module itself...

R_J · 07-01-2025, 03:46 PM

The problem is likely in the power supply, grey box on the left, I would start by replacing C1324 (560µf/35v) in the primary, then check the secondary caps

R_J · 07-01-2025, 12:45 PM

It is likely the diode that is bad, you can't really check them, they are a stacked diode, the cap value is not critical. Good to hear it is working
It is possible the cap is shorting under load, but the diode is more likely.

R_J · 06-30-2025, 09:53 PM

Looks like DC_DET is logic low, not sure what it should be I suspect it should be +3.3v . There is a DC detect check test point (page 104 k,3) it seems to have logic levels, check those pins, maybe it will show something wrong
This is not a simple system, they monitor a lot of things, and anyone could cause a fault. and they don't really say if a logic high or low is normal operation or with fault.

R_J · 06-30-2025, 11:21 AM

If you replaced the amp/power board and disconnect CN501 (twamp) and still have the protection led, check CN255 pins 15 (DC_DET) and 16 (AMP_ERR) to see which line is enabling the protection.

IC501 is operating in btl (bridge mode) so KG is common or signal ground...

R_J · 06-30-2025, 10:01 AM

You say there is a fuse in the high voltage secondary lead that blows? if this is the case, it is not the transformer and more likely the diode or cap.
Usually, the problem is the door switch is bad (stuck closed) and the monitor switch closes blowing the main fuse.
I supplied a diagram, your transformer connections to the magnetron, cap, diode should be similar
I have had shorted components (cap, diode etc.) on the secondary and they would load the transformer causing it to hum very loud but not blow the fuse instantly.
it is rare for the transformer to go bad, and it...

R_J · 06-29-2025, 08:06 PM

`What point are you using for ground when checking the tweeter voltage? Check what voltage you have ACROSS the tweeter terminals, the supply to this ic is +55v, half would be around +27v measured to PGround
The speaker is connected across the two outputs of the ic.
Are you able to power on the amp without the tweeter amp board connected?

R_J · 06-29-2025, 07:40 PM

The actual number is an Alpha & Omega AON6520 Digikey says Rohm RQ3E120BNTB is a direct replacement, I'm sure there are others

R_J · 06-29-2025, 07:24 PM

I found them on another site. Looks like the board is a JWBX-12V5A-A

Post #6 can be removed to save space...

R_J · 06-29-2025, 02:04 PM

The 1M seems to be a (Fairchild) MMBTA13LT1G, the B97 could be a 2SB1197A

R_J · 06-29-2025, 01:34 PM

Best the wayback machine can supply...

R_J · 06-27-2025, 11:35 AM

The high voltage winding has one end connected to the core (ground) they all have that., the other end of the high voltage winding is either a wire lead with spade connector or just a spade connector on the transformer. The other leads are for the filament and are only a couple turns around the core to provide around 3 volts
The FTR and EMR seem to be more similar, maybe lead length is different?

Is the one you have defective?...

R_J · 06-26-2025, 04:11 PM

.

R_J · 06-25-2025, 06:07 PM

seems to be a slight difference in where one of the secondary leads comes out? they should be functionally the same...

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