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Help with a mtx thunder 1000xd
Help with a mtx thunder 1000xd
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Old 8th July 2019, 04:58 PM   #1
Albis2985 is offline Albis2985  Panama
diyAudio Member
 
Join Date: Jun 2019
Default Help with a mtx thunder 1000xd

Help with a mtx thunder 1000xd

I request your help and knowledge since it is the first time that an amplifier arrives at the workshop, the led turns green but there is no oscillation in the gate of the mosfet of the source. I checked everything around tl494 and found nothing wrong.

Sorry my english is not so good

attached voltages of tl494c and lm339

tl494
pin 1 0.02V
pin 2 4.8V
pin 3 0.05V
pin 4 5V
pin 5 1.5V
pin 6 3.3V
pin 7 0 V
pin 8 12V
pin 9 0V
pin 10 0V
pin 11 12V
pin 12 12V
pin 13 4.9V
pin 14 4.9V
pin 15 4.9V
pin 16 0V

lm339
pin 1 0.7V
pin 2 4.9V
pin 3 12V
pin 4 0.6V
pin 5 3.1V
pin 6 0.8V
pin 7 3.1V
pin 8 3.6V
pin 9 5V
pin 10 5V
pin 11 7V
pin 12 0V
pin 13 0.6V
pin 14 0.6V
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Old 8th July 2019, 08:00 PM   #2
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
The LM339 could be defective. I don't have a diagram for this amp but MTX typically uses the remote voltage to drive the high/low voltage protection which turns on the 494. With the voltages on pins 8-11, pins 13 and 14 should be high. There could be some other input to the circuit. I would try lifting pins 13 and 14 to see if that will allow the amp to power up.
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Old 8th July 2019, 08:47 PM   #3
Albis2985 is offline Albis2985  Panama
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Join Date: Jun 2019
thanks for responding Perry, I already chose to change the lm339 without any results, I will try raising the pins 13 and 14 of lm339 once I return to the workshop as you indicate and I will tell you the result.
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Old 8th July 2019, 08:47 PM   #4
Albis2985 is offline Albis2985  Panama
diyAudio Member
 
Join Date: Jun 2019
thanks for responding Perry, I already chose to change the lm339 without any results, I will try raising the pins 13 and 14 of lm339 once I return to the workshop as you indicate and I will tell you the result
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Old 8th July 2019, 09:00 PM   #5
Albis2985 is offline Albis2985  Panama
diyAudio Member
 
Join Date: Jun 2019
thanks for responding Perry, I already chose to change the lm339 without any results, I will try raising the pins 13 and 14 of lm339 once I return to the workshop as you indicate and I will tell you the result
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Old 9th July 2019, 02:03 PM   #6
Albis2985 is offline Albis2985  Panama
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Join Date: Jun 2019
Hello Perry I did what you told me about lifting pins 13 and 14 of Lm339 but without success, the amplifier still does not oscillate, any other suggestions where I should follow the trail to make the amplifier turn on?
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Old 9th July 2019, 02:55 PM   #7
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
There is a transistor connected between pins 4 and 14 of the 494. If you remove it, pin 4 should drop to 0v and the amp should power up.

If they are using this configuration, you need to find out what's pulling the base of that PNP transistor down.
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Old 11th July 2019, 05:37 PM   #8
Albis2985 is offline Albis2985  Panama
diyAudio Member
 
Join Date: Jun 2019
Hello Perry today I was reviewing the amplifier but I did not see any PNP transistor connected with pin 14 of tl494 I only see a 10K resistor connected to pin 4 of tl494, I found the d207 that was not overheating but lifted everything close to it but everything marks me well out of the circuit some other suggestion to continue reviewing?
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Old 11th July 2019, 06:36 PM   #9
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
Post good quality photos of the area around the power supply control ICs on both sides of the board.
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