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Old 12th December 2010, 05:04 AM   #1
ivkata is offline ivkata  United States
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Default Power acoustik lt1920-2 amp stuck in protect mode psu ishue

this amp is stuck on protect mode.All outputs and power transistors tested fine no burn resistors or bad th .when i apply power to the amp it dosent feel like powering on .there is NO power on the gates of the irf44n none on even 1 of the 12 all gate resistors are good ,board was inspected and no burn tracks or any signs of previous repair or damage .it have the kia494 voltage contoroler im assuming this might be the problem but im just newbie seeking advice from the more competent

Last edited by ivkata; 12th December 2010 at 05:07 AM.
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Old 12th December 2010, 05:11 AM   #2
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Post the DC voltage on all 16 pins of the 494. Place the black meter probe on the amplifier's ground terminal. Place the red meter probe on the point where you need to measure the voltage. Copy and paste the following into your next post.


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:
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Old 12th December 2010, 05:30 AM   #3
ivkata is offline ivkata  United States
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Pin 1: 0.06
Pin 2: 5.4
Pin 3: 5.3
Pin 4: 0.2
Pin 5: 1.7
Pin 6: 3.8
Pin 7: 0.00
Pin 8: 15
Pin 9: 0
Pin 10: 0
Pin 11: 15
Pin 12: 14.2
Pin 13: 5.5
Pin 14: 5.5
Pin 15: 5.5
Pin 16: 11.7
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Old 12th December 2010, 05:41 AM   #4
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Location: Louisiana
Do you have a current limiter for your power supply?

If not, you'll need to insert a 10 amp fuse into the B+ line before you continue. Have all transistors tightly clamped to the heatsink before applying power.

Is there a Q1 with its emitter connected to pin 12 of the 494 and its collector connected to pin 5 of the 8 pin op-amp? If there is, pull it and power it up.
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Old 12th December 2010, 06:17 AM   #5
ivkata is offline ivkata  United States
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yep i have this q1 trnasistor its a1266 i removed it and the same story no gate voltage
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Old 12th December 2010, 06:25 AM   #6
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Post the DC voltage on all 8 pins of the op-amp. I'm assuming that you confirmed the transistor was connected as described.


Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
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Old 12th December 2010, 06:42 AM   #7
ivkata is offline ivkata  United States
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Pin 1: 12.3
Pin 2: 12.5
Pin 3: 7.4
Pin 4: 0
Pin 5: 0.82
Pin 6: 5.5
Pin 7: 1.5
Pin 8: 14.4

yes i verified that Q1 was conected exactly as described
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Old 12th December 2010, 06:53 AM   #8
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This op-amp appears to be defective but we need to check a few more things. .

Is the thermistor in the board?

If you desolder one leg of the thermistor, what's the resistance across it's terminals?
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Old 12th December 2010, 07:14 AM   #9
ivkata is offline ivkata  United States
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there are 3 termistors in this amp 1 on each chanel and 1 on the psu
psu termistor shown 82k
both chanels showed ~ 90k
all tested with one leg of the pcb
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Old 12th December 2010, 07:27 AM   #10
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Solder them back into the circuit. For the one in the power supply, with your multimeter set to ohms, confirm that one leg is directly connected to ground and the other is directly connected to pin 2 of the op-amp.

Check D2 to confirm that it's not shorted or leaking.
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