Mtx ta81001 resistor problem

[kfx5050]

Can someone help me out on a repair? Have a mtx ta81001 have 5 off them fix 4 of them.but the fifth one is giving me trouble. Resistor r147 and 148 burn up as soon I apply power to the remote input on the amp.do anyone know what might be my issue or hack fix the problem. I also can post pictures if the bord parts if any needs help replace a burnt part.

 

[Perry Babin]

Post the resistance of R318 and R319 near the RCA op-amp.

Does it burn the resistors if you disconnect the preamp board?

 

[kfx5050]

Yes it burns the resistors. R318 is 1.000 kohms and R319 showing .991kohms

 

[Perry Babin]

Those are 100 ohm resistors so they have failed. That generally indicates that the voltage regulators have failed. Have you replaced all of the failed components around the two regulators?

 

[kfx5050]

No. I only replace them two RESISTOR. R147 and R148 I dont see any ather burnt components. Where are the voltage regulatory at?

 

[Perry Babin]

Those large resistors and all of the components in the immediate area form the voltage regulators. The transistors and SMD diodes won't generally have any visible signs of damage. Some of the smaller resistors have visible damage when they fail but you often need a magnifying glass to see it. The transistors clamped to the heatsink (likely IRF540) may also be damaged. The negative regulator may have additional components near the opto-couplers.

You should also know that there is likely extensive damage to the preamp board.

Do NOT apply power to the amp without having all components tightly clamped to the heatsink.

If this amp drives the fans from the positive regulator and it has failed as well, all fans will likely need to be replaced.

 

[kfx5050]

Ok. I replace all the irf540 on the side where the Rca jacks are at. So I need to replace both side?

 

[kfx5050]

If I power up the amp woth out the irf540 that's right in fornt of the two resistor they dont blow. But onces k soldier on in them two blow.

 

[kfx5050]

I will by some replace parts and see what happens. Will keep you posted

 

[kfx5050]

But the fans do works. If the power left hook up and I unhook the remote wire after about 2 mins the fan kick on

 

[Perry Babin]

Not all amps have the fans connected to the regulators.

The resistors didn't burn with the FETs out of the circuit because they were disconnected from the circuit with the absence of the FET.

Did you check all transistors, resistors and SMD diodes in the regulator circuit?

 

[kfx5050]

Ok checking them now.the transistors do i need to remove them from the bord in order to check them?

 

[Perry Babin]

Yes. Lift 2 legs and you can check it without other components interfering with the readings. You have to check for shorts, open junctions and leakage.

 

[kfx5050]

Ok fount the problem rec100 and and rec102 are shorted. On the compount it say cq507 and under that set of number is says u1540. Where or what would b a good replacement?

 

[kfx5050]

here a pic

The is the shorted part I have fount

 

[S Merlington]

Did you test this part in or out of the amp?

With the 1540 out of the amp set your meter to diode check

Post your readings between the legs as followed

Legs 1-2:
Legs 1-3:
Legs 2-3:

 

[Perry Babin]

#15:
It's an MUR1540. Are you absolutely sure that it's shorted? For one to be shorted would be unusual. For two to be shorted would be very unlikely.

#16:
It has only two terminals.

 

[kfx5050]

Yes. When I get home I will post the readings of the other transistor and the reading I get from the two leg transistors.

 

[kfx5050]

Ok im back got all of the transistor remove which leg do I test?

 

[Perry Babin]

Read THIS.