MTX 6001 (red protect light)

[scampo77]

i have a new amp here mtx 6001 the red light comes on as soon as i put power to it. on one side i have big TO-247 i suspect is the outputs (IRFP240) x6 and on the other i have TO-220 cases 75339P (i suspect is the power supply)

on my TO-247 i have full 62v to the gate. and on the gates of my TO-220 i have -1.2v

should i pull the 75339P? are these the impossible to find ones?

thank you always to everyone here!!

 

[Perry Babin]

For each of the outputs, place the black probe on leg 3 and the red probe on leg 1. Post the voltage for each set of 3 outputs.

Do you have DC on the speaker terminals?

 

[scampo77]

on the first 3 i have ~9v and the 3 on the right hand side i have 0v

and yes 58v on the + speaker terminals (is that full rail voltage?)

 

[Perry Babin]

If the voltage is equal to the voltage on the center leg of the FETs with 9v, yes. I'm assuming that those FETs have essentially the same voltage on legs 2 and 3.

Can you take a good enough photo to allow the silkscreen to be legible?

 

[scampo77]

i can but i have to take small pictues cause the camera is so close to the board did you need everything or just a specific part?

by silk screen i assume you mean all the part numbers on the components

 

[Perry Babin]

The photos don't have to cover a large area.

The silkscreen is the white text printed on the board.

At this point, I need to see the area in the red square.

 

[scampo77]

i did my best for pictures of the entire right hand side

my outputs are 58v (first 3) and -62v (last 3) on leg 3

 

[Perry Babin]

Is R502 burned?

Do any resistors (or any other components) appear to have overheated?

 

[scampo77]

yes its burnt and it looks like the 2 next to it are possibly missing. R510 and C504


do you happen to have a diagram for this amp? or should i call mtx?

 

[Perry Babin]

I don't have anything on this amp. You can see if MTX will tell you what the values are or if they were omitted intentionally but don't expect any help if you're trying to get a schematic diagram from them.

 

[scampo77]

oh lovely

can you tell from my photos if this is the reason it is going into protect?

ill try to give them a call this week and ill keep you posted

thanks

 

[Perry Babin]

I haven't had time to study the photos yet. I think you need to determine if the missing components are supposed to be there. You also need to replace those that are burned. Repair all known problems then we'll work from there.

 

[scampo77]

with all the power of my charm i talked to MTX and got a nice guy at tech support and he said he could give me values for the burnt and missing parts.

R502 1k ohm
R510 not used
C504 not used

should i replace the 1k ohm and try to power up again? via a big resistor?

 

[Perry Babin]

Replace it. If it begins to overheat, Post the DC voltage on all pins of the op-amp (U501?).

 

[scampo77]

yes it over heated, the red protect light is still on. i cant seem to find a data sheet for this op amp the markings on the IC are..

KG27
NE55
32D

all i could find was a NE555 but this seemed to be something in a TO-220 case.

without knowing which pin is #1 all the pins are reading ~50v

there is a recessed dot in the corner of the IC does this indicate pin 1?

 

[Perry Babin]

NE5532

Yes. The dimple is pin 1.

 

[scampo77]

1. 55v
2. 50
3. 50
4. 52
5. 57
6. 50
7. 50
8. 50

 

[Perry Babin]

Are you sure that you have the pin numbering right? I would expect pin 4 to be tle lowest and pin 8 to be the highest.

Do the rest of the op-amps have ±15v on pins 4 and 8?

 

[scampo77]

yes, i had the pins mixed up, sorry

1. 55
2. 50
3. 50
4. 52
5. 50
6. 50
7. 50
8. 57

the op amp next to this one is at location U502

1. -62
2. -62
3. -61.4
4. -62
5. -48.7
6. -48.9
7. -61.9
8. -48.8

i have only the 2 opamps with 8 legs but i have 1x TL494C 1x LM339 and
2x 074C / EZ38641. these have 16 legs and are in a different part of the board

 

[Perry Babin]

What is the DC voltage on the power supply pins of the TL074s?

Is pin 4 of U502 directly connected to the negative rail?