sundown 3500

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i have a sundown 3500 that came in with shorted outputs, the amp was working perfectly but was stored for around 9 months, when the customer wired it back into the car it went straight into protect.
i have replaced all the outputs and the driver board, now the amp powers fine and when audio is applied it has a clean output till around 50% power then starts to pulse output on and off almost like it has audio then mute then audio then mute, if i turn the gain down the amp has clean output.
the only thing i have done different is replace the 1rfp360 with 24n40
You mentioned the position of the gain. Do you believe that there is a problem with the gain control? Or is the problem with the output level and the amp will cut out again at low gain if enough signal is driven into the amp?

If the problem is only with the output level, please don't mention the gain control. It adds another variable and makes troubleshooting more difficult.
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There are two resistors driving pin 3 of the center group of pins. One is a high value, the other is a lower value (6-8-10k typically). On the leg of the low value resistor that is NOT connected to the driver board, is the audio constant (not dropping out) when the audio at the speaker terminals drops out?

Is the relay disengaging when the audio drops out?
I don't think it's the outputs with the symptoms that you've given. If it were the outputs, I'd expect that the amp would draw excessive current or the rail-rail oscillation would be irregular or intermittent but you stated that it was continuous

Do you see the rail-rail carrier being modulated (changing pulse width) by the audio when there is audio?

Do you see the modulation of the carrier when the audio drops out?
Sorry for bringing back an old thread.

I am also about to order parts for a Sundown SAZ-3000D but I have plenty of fda24n40 on hand and I feel like I would use it instead of IRFP360LC .

I would just like to know confirm if replacing IRFP360LC with fda24n40 will not cause any problems just like the thread started had?

Vgs th - Gate-Source Threshold Voltage:
fda24n40 = 3V
IRFP360LC = 2V

Qg - Gate Charge:
fda24n40 = 60 nC
IRFP360LC = 110 nC
I always use FDA24N40F instead of IRFP360LC in all cases.
No problem at all.
FDA24N40F are better and faster and (important) easier to drive and in case of amplifier with irs21844 that drive it directly, is definitely a huge benefit.
Globally, the amplifier aquire reliability and BETTER sonic performance (due to easier drive), this means that sonically, seems to listen a bigger amp but not in terms of power.
Better performance, faster response to frequency transient and little bit improved efficiency.
In most cases (IMHO in all cases) no gate resistor change are needed, simply unmount IRFP360LC and mount FDA24N40F.
Absolutely no problem.
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