Ok, so here is my next victim. An mtx thunder 600xd. Does anyone has a picture of this amp? It seems to be missing a lot of components by the lm339. I don’t know if they were left off at the factory, or the got removed by someone else. Just comparing the circuit with a 2301 i have at the bench the circuits and even designations are similar and they indeed seem to be missing. I did remove the ps fets, a rectifier, the inductor and an output cap. I did mess around with a diode by the power terminals, and the transistors by the 494. The area that i’m concerned with is the center of the board before i move on with further troubleshooting.
So far for the testing i’ve done like it sits the only thing that got my attention is that the 494 has straight 12v on pins 8 and 11. No oscillation. Pin 5 has a nice sawtooth. It has a green light(i think) its kind of yellow orange. But definitely not red. I saw it turn red when i pulled the diode by the power terminals.
Any takers?
Thanks for the help.
So far for the testing i’ve done like it sits the only thing that got my attention is that the 494 has straight 12v on pins 8 and 11. No oscillation. Pin 5 has a nice sawtooth. It has a green light(i think) its kind of yellow orange. But definitely not red. I saw it turn red when i pulled the diode by the power terminals.
Any takers?
Thanks for the help.
Attachments
Copy and paste and post the DC voltage on all terminals of the 494:
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
Ok, here are the numbers on the 494:
Pin 1: 0.007
Pin 2: 4.835
Pin 3: 0.074
Pin 4: 5.057
Pin 5: 1.542
Pin 6: 3.449
Pin 7: 0.003
Pin 8: 11.15
Pin 9: 0.004
Pin 10: 0.002
Pin 11: 11.15
Pin 12: 10.42
Pin 13: 5.070
Pin 14: 5.069
Pin 15: 5.069
Pin 16:0.001
Now here is a thing. They measure the exact same with the remote off. So i decided to chase the remote signal and it goes:11.7v to r225. From r225 1.2v to one side of d206 and o.6 out of d206. Stopped there so i could post the 494 numbers, but it doesn’t seem right. That path continues on to the top 339 on the pic iir.
_____
Pin 1: 0.007
Pin 2: 4.835
Pin 3: 0.074
Pin 4: 5.057
Pin 5: 1.542
Pin 6: 3.449
Pin 7: 0.003
Pin 8: 11.15
Pin 9: 0.004
Pin 10: 0.002
Pin 11: 11.15
Pin 12: 10.42
Pin 13: 5.070
Pin 14: 5.069
Pin 15: 5.069
Pin 16:0.001
Now here is a thing. They measure the exact same with the remote off. So i decided to chase the remote signal and it goes:11.7v to r225. From r225 1.2v to one side of d206 and o.6 out of d206. Stopped there so i could post the 494 numbers, but it doesn’t seem right. That path continues on to the top 339 on the pic iir.
_____
There is likely a PNP transistor that's connected between pin 14 and pin 4 of the 494. Remove it. The amp should power up, even without remote.
If it doesn't, see if any voltages on the 494 have changed.
If it doesn't, see if any voltages on the 494 have changed.
Well, took me a minute to figure out, but i was able to track down that transistor. It goes from pin 14 to c109 to the trancistor q101 tru capacitor c105 under the 494 and to pin 4.
Just like you said, the 494 is alive, and i’m getting drive on pins 8 and 11 to the transistors, tru the small transformer and up to the base of the fets. I didn’t get to test the transistor, it’s 4am here in ga, my extractor decided to suck up the transistor and i dropped the hot iron on my lap, so i’m calling it a night and i’ll get back at it tommorow.
Btw, i have been using a schematic that i’m pretty sure you linked for a sony amp and it’s actually fairly close to these mtx amps i’ve been messing with. Here it is http://www.bcae1.com/temp/sony - XM-D400P5_Car Power Amplifier SM.pdf
Again thanks for the help.
Just like you said, the 494 is alive, and i’m getting drive on pins 8 and 11 to the transistors, tru the small transformer and up to the base of the fets. I didn’t get to test the transistor, it’s 4am here in ga, my extractor decided to suck up the transistor and i dropped the hot iron on my lap, so i’m calling it a night and i’ll get back at it tommorow.
Btw, i have been using a schematic that i’m pretty sure you linked for a sony amp and it’s actually fairly close to these mtx amps i’ve been messing with. Here it is http://www.bcae1.com/temp/sony - XM-D400P5_Car Power Amplifier SM.pdf
Again thanks for the help.
Thanks for the tip, i’ll definitely try that. As for the transistor, i tested it. As far as i can tell its good. I think, now that i’m typing i’m questioning my measurements.
On diode mode, positive probe on pin 1 i get 0.6 to pin 2 and 0.6 to pin 3. No other combination of probe placement shows voltage. Is this correct? To me it seems backwards 1 positive and 2 negatives, making it and npn but it is a GM2? I’m going to test it again. I tested the resistor that goes across this transistor, and it checked good. Also traced pin one of the transistor tru a diode d211 and a resistor r248 to pin 13 of the bottom 311. The diode checked ok on circuit, but i might pull it to see.
One thing, is it possible that there’s some sort of feedback preventing the 494 to operate with the fets removed? The ps fets were good on this amp, but i pulled them and a rectifier to fix the 2300 i was messing with.
On diode mode, positive probe on pin 1 i get 0.6 to pin 2 and 0.6 to pin 3. No other combination of probe placement shows voltage. Is this correct? To me it seems backwards 1 positive and 2 negatives, making it and npn but it is a GM2? I’m going to test it again. I tested the resistor that goes across this transistor, and it checked good. Also traced pin one of the transistor tru a diode d211 and a resistor r248 to pin 13 of the bottom 311. The diode checked ok on circuit, but i might pull it to see.
One thing, is it possible that there’s some sort of feedback preventing the 494 to operate with the fets removed? The ps fets were good on this amp, but i pulled them and a rectifier to fix the 2300 i was messing with.
The transistor appears to be OK. It was the quickest way to get the amp to power up.
It's likely driven by one of the terminals of the LM339. Find which terminal of the 339 drives it.
It's likely driven by one of the terminals of the LM339. Find which terminal of the 339 drives it.
One more thing, did some poking around and found a pic of this amp. It seems that it’s missing the same components as mine. The one on the pic is a 7801 if i’m not mistaking. The only big difference that i see is, q214 and c11 that also the 2300’s that i have, have them installed also. But i didn’t notice any signs of work/rework on that area.
Attachments
Pin 13 appears to be the one driving it, but there’s a resistor that goes on the bottom side of the diode that connects to pin 9 of the 339.
I got some measurements on the 339’s with the remote connected:
The transistor that powered the amp when removed is connected to U2.
339 (u2)
Pin 1: 0.000
Pin 2: 0.000
Pin 3: 10.411
Pin 4: 0.981
Pin 5: 0.098
Pin 6: 0.073
Pin 7: 0.074
Pin 8: 2.500
Pin 9: 0.070
Pin 10: 0.016
Pin 11: 1.500
Pin 12: 0.003
Pin 13: 0.101
Pin 14: 4.64
339 (u1)
Pin 1: 0.496
Pin 2: 4.769
Pin 3: 10.420
Pin 4: 0.570
Pin 5: 3.19
Pin 6: 0.945
Pin 7: 3.191
Pin 8: 3.281
Pin 9: 5.00
Pin 10: 5.00
Pin 11: 6.562
Pin 12: 0.003
Pin 13: 0.670
Pin 14: 4.652
The transistor that powered the amp when removed is connected to U2.
339 (u2)
Pin 1: 0.000
Pin 2: 0.000
Pin 3: 10.411
Pin 4: 0.981
Pin 5: 0.098
Pin 6: 0.073
Pin 7: 0.074
Pin 8: 2.500
Pin 9: 0.070
Pin 10: 0.016
Pin 11: 1.500
Pin 12: 0.003
Pin 13: 0.101
Pin 14: 4.64
339 (u1)
Pin 1: 0.496
Pin 2: 4.769
Pin 3: 10.420
Pin 4: 0.570
Pin 5: 3.19
Pin 6: 0.945
Pin 7: 3.191
Pin 8: 3.281
Pin 9: 5.00
Pin 10: 5.00
Pin 11: 6.562
Pin 12: 0.003
Pin 13: 0.670
Pin 14: 4.652
Yes, the transistor is back on. All those measurements were performed with the transistor installed.
No power applied, what's the resistance between pin 13 of U2 and the base of the transistor?
What's the resistance from the base to the emitter of the transistor?
What's the resistance from the base to the emitter of the transistor?