Blown TE1501DR need help

[mbates14]

I have all these components blown and replaced them:

c413
r118
q106
q110
r145
r146
fet191
d104
q107

Amp fired up with diagnostic LEDs lit where they should be... however i had no sound, and the VU LED action from the EFX board wasnt working either....

So i removed the upper ribbon connected board which the pots reside one, and found 2 blown TL074 op amps and a couple of burned resistors plus 2 open resistors. Swapped all these out, and still had no sound with no VU action, heard the thump in the speaker like most of the MTXes do on powerup. One of the 074s got hot and then all those new components i replaced blew up again, nice light show... I am thinking all these components made up a switching or possibly linear 15V regulator as it has a 15V zener inside its circuit. which failed shorted along with numerous other components on the explodition rampage.

Why do these MTX Class-D amps have to be such a pain in the ******* ***?

I had another thread elsewhere in this forum, and found out it was in the wrong area. so i reposted it here. sorry....

[Perry Babin]

If you don't clamp the regulators TIGHTLY against the heatsink, they will fail within seconds (especially the +15v reg).

It sounds like the reg has failed. Without the preamp board plugged in, measure the DC voltage on pins 4 and 8 of the op-amp near the RCA jacks. Do you have ±15v on those pins?

[mbates14]

Yea i know, i had to fight and fight and fight with that stupid heatsink, because the output transistors are TO-247 based i think is the type, and they wouldnt rest right without hitting a lip.

But yes, i had it all clamped down. the regulator was blown up when i got it. I replaced all those parts, and it ran again. but no sound. the service LED was lit, and a LED near the 2 NE5532 op amps and the mosfet driver opto-isolators was lit. I repalced both those op amps and drivers because there was a 10uf 25V cap popped up in that area. so i didnt wanna take the risk, and replaced those parts. I also replaced the LM311 as well.... checked all those areas for shorted diodes/transistors, came up empty.

However, i had no audio, and no action from the LEDs on top. usually when audio hits the amp, the LEDs start chanigng colors and pulsating, they were doing nothing. staying on one color.

Thats when i discovered the two highly overheated TL074s, and couple burnt resistors and 2 open resistors. This is probably how the regulator blew in the first place.....

So i swapped all 4 resistors, they were all 10ohm, and replaced both TL074s from another scrap amp board. i didnt have new ones, which may have been a problem, but i doubt it.

Tried to fire the amp up again, and same deal. no sound. then eventually after dicking with it for awhile, the 2 1ohm resistors blew again, and the IRF540 mosfet shorted again, all the same parts i replaced the first time around blew again..... while i noticed one of the TL074s started getting hot again. I think that EFX board where the 074s are located is shot, taking out regulators. heck i dunno.

Also, there are 2 LEDs near the RCA jack chip, whcih is a TL072 i believe, and netiher of thoes LEDs ever lit up. the short and protect LEDs were off as well...

[I Am An Idiot]

Is there plus and minus 15 volts on the op amp located near the RCA jacks?

[Perry Babin]

The LEDs near the RCAs only light up when there is DC on the RCA jacks (as when driving it directly with a head unit's speaker outputs).

Get it working without the preamp board. Jump the pins in the header as shown in the attached image. The audio won't be loud but you can get it working and determine if the regulator is going to be reliable. The fans operate off of this regulator so you may want to disconnect them (they're likely damaged) while you're troubleshooting.

[mbates14]

When i get back into the shop tomorrow, ill check things out.

[mbates14]

before the regulator blew up again, the fans would spin for a half a second and shut off when u would first power the amp up. But i never tested any voltages anywhere because i didnt have a schematic to go by, i was still screwing around with that preamp board.

[mbates14]

I rebuilt the regulators again, I have verified a positive and negative 15V on the RCA jack op amps. I replaced the NE5532s again just to be on the safe side, as this is the driver circuits for the outputs i assume.

Anyway, on power up, when the red LED comes on, i get some hiss and a motorboating sound that declines in frequency as the amp is left on longer..... Also i DO hear sound from the speaker, although very weak. But audiable none the less, HOWEVER after a few seconds when the motorboating and hiss settles down, the audio fades away to nothing.

so im lost. any ideas?

[mbates14]

If preamp board is plugged in, no more motorboating and hiss.... but no sound either. so preamp board bad.

[Perry Babin]

Confirm that you have both positive and negative voltage on the power supply pins of the audio op-amps on the preamp board. I think there are resistors for the supply for each op-amp and if one is open, the amp won't work.