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Old 8th March 2008, 06:28 PM   #1
clayton is offline clayton  United States
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Join Date: Apr 2004
Location: LA.
Default LInear Power 2502IQ

When I got this amp it would not power on. Took of cover & c19 had blew up. Q5 is connected to c19 & it also was bad. Replaced both and now it powers up but it will only run for about 5 min then the power led starts going dim and sound stops coming out. If I connect & disconnect turn on wire led trys to come back on but then goes back dim. If I let it sit for a few min it will come back on. By the way c19 & q5 are part of the turn on. Any suggestions on what needs to be checked?
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Old 9th March 2008, 10:48 PM   #2
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Location: Louisiana
Compare the voltage on the SG3526 when it's working properly and when it's shutting down. That may help you to trace the source of the problem.

Also check the voltages on the 555 and the 6 pin opto-coupler.

There's a small driver transformer just behind the power transformer. Resolder the leads on it on the top 'and' the bottom of the board.

Q5 is part of the regulator circuit. It controls the amount of current driven into the driver transformer.

If I'm not mistaken, the remote feeds Q1 which delivers power to the 3526.
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Old 10th March 2008, 01:14 AM   #3
clayton is offline clayton  United States
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Join Date: Apr 2004
Location: LA.
I was not able to get it to power up all the way. Led comes on then goes dim right away. Anyway here are the readings I got with it like this.
SG3526
pin 1: 5v pin 2: 0
pin 3: 4.2v pin 4: 4.66v
pin 5: 5v pin 6: 0
pin 7: 0 pin 8: 4.96v
pin 9: 3.65v pin 10: 4.98v
pin 11: 12.25v pin 12: 5.2v
pin 13: 0 pin 14: 11.9v
pin 15: 0 pin 16: 0
pin 17: 0 pin 18: 1.8v

555 timer
pin 1: 0 pin 2: 12.25v
pin 3: .4v pin 4: 12.25
pin 5: 12.25v pin 6:.01
pin 7: .01v pin 8:8.18v

6 pin opto-coupler
pin 1; 7v pin 2: 6.4v
pin 3: 0 pin 4: 0
pin 5: 12.25v pin 6: 0
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Old 10th March 2008, 08:19 AM   #4
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Pin 17 should have 12v. Trace it back to see if you can determine why voltage isn't present. It appears that it may go through a resistor. The resistor may be open.
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Old 10th March 2008, 11:00 PM   #5
clayton is offline clayton  United States
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Join Date: Apr 2004
Location: LA.
I was able to get it to power up long enough to get my readings.
SG3526 had only 2 changes pin 15 is 5.1v & pin 16 is4.4v pin 17 stayed at 0v. The opto-coupler pins 1,2 & 3 went to 24v.
Thge resistor connected to pin 17 of the SG3526 is fine. I got a reading of 18k
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Old 11th March 2008, 12:22 AM   #6
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I'm relatively sure that pin 17 must have ~12v for the IC to operate. Are you sure you're not mistaken on the pin numbers?
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Old 11th March 2008, 01:20 AM   #7
clayton is offline clayton  United States
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Join Date: Apr 2004
Location: LA.
My bad I was reading pins 10 - 18 backwards. Pin 17 has 12v with & without it functionig properly. Pins 12 & 13 are the only one that change when amp is working. Pin 12 is at 4.4v & pin 13 is at5.1v. Sorry about the confusion.
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Old 11th March 2008, 01:33 AM   #8
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13 and 16 should have the same voltage. If one goes to 0v, the other should also.

What other component connects to pin 12?
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Old 11th March 2008, 02:13 AM   #9
clayton is offline clayton  United States
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Join Date: Apr 2004
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I am not sure but there is only one trace on the top of the board that goes under the ic. I think this connects to pin 12 The trace goes to either a 50ohm or 51ohm resistor. When measured it reads 50ohm. The only reason I am not sure of its value is the first band on the resistor is either green or blue,both look the same to me (guess I might be a little color blind or need glasses). The other leg of the resistor goes to pin 17. Form that point it splits off & goes to 2 caps by pin 17 & going the other way it goes to another resistor. This resistor measures 18k ohm in circuit. According to the color code it should read 26k ohm.
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Old 11th March 2008, 09:22 AM   #10
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Join Date: Nov 2003
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If you're unsure about the connection between pin 12 and the resistor, use your meter to confirm that there is a 0 ohm connection between them. If the other side of the resistor goes to pin 17, there's no point in tracing it further unless the voltage on pin 17 is dropping.
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