MTX 6001 (red protect light)

[scampo77]

U502 is 0 ohm to the Neg lug where the main power comes into the amp

i have 2x TL074s did you want just the pin 4 Vcc+ measurement? or all the legs?

 

[Perry Babin]

Pins 4 and 11 on the TL074s.

 

[scampo77]

with the black lead on the main ground coming into the amp and the red on the pins i got...

location U300
4. 29v
11. -.5v

U401
4. 29v
11. -.5v

but the pin 11 on both are moving around from 0 to -.9v neither is static like the 29v

and i keep getting the 1k resistor (R502) so hot it keeps melting off the board.

 

[Perry Babin]

Is D401 or D402 shorted?

Is C402 or C403 shorted?

 

[scampo77]

i feel like a idiot but after a hour of staring at this board i can only find D401 and its not shorted.

i can find all the surrounding numbers but i cant find them anywhere. should i follow a trace backwards to find what im looking for?

 

[Perry Babin]

I've been using photos that I have of an 8001 since they were more complete. It appears that the amps are similar but there are differences. In your amp, the diodes in your amp are likely D400 and D401. Your amp doesn't have the capacitors. When you power up the amp, do any of the op-amps get hot?

 

[scampo77]

oh good i was afraid i was possibly wasting your time by not being able to find the components.

D401 is 35k ohms both directions and D400 is 50ohms both directions. that is tested in the board i can pull them if need be.

yes 2 op amps are getting hot. U502 (LM311) + U501 (NE5532D)

 

[Perry Babin]

Remove the 5532. Does that allow the TL074s to have ±15v on pins 4 and 11?

 

[scampo77]

nope unfourtunatly, i have .5v on all 4 pins

 

[Perry Babin]

For diodes D400 and D401, one end of each diode should be connected to the other diode. Those ends should be connected to ground (either the input RCA shield ground or the main ground for the amp). Which ground are they connected to?

 

[scampo77]

neither, they are connected to the neg speaker output. i have 5 ohms between each leg of the diode and both neg leads for the speakers. or atleast i suspect they are the negative leads i dont have the case on the amp anymore.

 

[Perry Babin]

The negative speaker terminals are at ground.

What is the voltage on each of the two regulator transistors (their bases connect to the other ends of these diodes)? List the voltage on all 3 legs of each regulator transistor.

 

[scampo77]

im not 100% im working on the correct transistors so i posted a picture,

can i put the NE55 back in before i lose it?

 

[Perry Babin]

I'd leave it out for now.

Has something changed? Earlier, you stated that you had 29v on the op-amps. They should get their voltage from these transistors but none of the pins have voltage on them. The center legs should have ±35v (or more).

 

[scampo77]

sorry, you were right i had pos and neg mixed up coming into the amp. i have +-46v at the regulators now

both controller TL074C have +-12v now

i have 46v at the #4 +VCC pad of the missing op amp and -33v at the #8 VCC pad of the other op amp.

i have the 4 ohm 40 watt resistor inline in the B+ terminal.

 

[Perry Babin]

What is the DC voltage measured directly across the speaker terminals?

 

[scampo77]

46v

 

[Perry Babin]

Are the outputs shorted?

Did you replace the output transistors?

 

[scampo77]

i havent changed them yet but i dont have any readings less then 1k ohms. (IRFP240)

PSU (75339P) i get them mixed up all the time but i dont have anything on that side less than 60 ohms.

 

[Perry Babin]

Remove Q518. Does the DC across the speaker terminals drop to 0v?