NC252MP Help

[bingaman]

I have an NC252MP that has failed and since it's out of warranty from anyone. I bought it used, it's in an Audiophonics MPA-S250NC XLR. After having it for about 18 months the left channel briefly went out and then the whole thing powered off. I did a brief inspection then and it looked like some caps had blown so I took it to a reputable repair place and had them replace the caps as I didn't feel like dealing with it. After recapping it is still showing the same issue, the power switch briefly lights up and then goes back off immediately. Subsequent presses of the power switch show nothing. What would anyone suggest I check here?

It never ran hot at all. It did have some light pops when I would power it up. I did not actually realize that there were two power switches so I did have it on top of a cabinet with the back switch on basically for 18 months straight and only used the front power switch to turn it on and 'off'. I never used the trigger.

 

[wwenze]

Bloated caps are often not the cause of catastrophic failure (They result in gradual degradation of performance) excepts in cases where the caps exploded.

From failing state description looks like left channel shorted and triggered overcurrent protection. Check the output transistors, located underside of the board sandwiched between the PCB and the metal plate.

 

[bingaman]

Below is what I got from Hypex, this all tested ok. I will check the transistors next. It sounds like the theory is it's powering on but enters protection mode, so it should show voltage on "J6.7 Output DC Error DC Offset detected, power supply disabled".

Check if four resistors are not open. Check diodes for shorts. Check U3. If 10R resistor next to it (when present, R267) is open U3 is bad.

Check 2R2 resistors R149/235. Check 15V Zeners.

If R149/R235 is burnt also check these four double diodes (BAV99). Same for other channel.

 

[LGD_]

This is why I use a vintage amp - I can fix it if the need arises (it hasn't so far)..

Good luck in getting your amp fixed .