LInear Power 2502IQ

clayton

Member
2004-04-05 1:56 am
LA.
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?
 
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.
 

clayton

Member
2004-04-05 1:56 am
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
 

clayton

Member
2004-04-05 1:56 am
LA.
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.
 
That makes sense since pin 12 is the sync input/output and there is no other oscillator for it to sync with.

At this point, I think you need to go back and confirm all voltages (working and not working). Be as precise as possible and confirm all voltages.

Working
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 17:
Pin 18:

Not Working
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 17:
Pin 18:
 

clayton

Member
2004-04-05 1:56 am
LA.
Here are the measurements:

Working

pin 1: 4.98
pin 2: 0
pin 3: 4.2
pin 4: 4.66
pin 5: 4.98
pin 6: 0
pin 7: 0
pin 8: 4.96
pin 9: 3.84
pin 10: 1.83
pin 11: .01
pin 12: 4.19
pin 13: 5.04
pin 14: 11.62
pin 15: 0
pin 16: 5.03
pin 17: 10.7~11.7
pin 18: 4.98

Non working

pin 1: 4.98
pin 2: 0
pin 3: 4.23
pin 4: 4.66
pin 5: 4.98
pin 6: 0
pin 7: 0
pin 8: 4.96
pin 9: 3.84
pin 10: 1.832
pin 11: 0
pin 12: 0
pin 13: 0
pin 14: 11.62
pin 15: 0
pin 16: 5.02
pin 17: 12.25
pin 18: 4.98
 

clayton

Member
2004-04-05 1:56 am
LA.
I retested all the pins & got better readings this time. I also noticed that when both channels are driven, in working state, they would fade in & out alternately. The left more than right channel. On previous power ups I was only useing the right channel.
This time it while runnig it popped the 15amp in line fuse. Volume maybe 1/4 way up. Speakers are 8ohm home speakers if that makes a difference.

Working
pin 1: 4.99
pin 2: 0
pin 3: 4.21
pin 4: 4.68
pin 5: 5.01
pin 6: 0
pin 7: 0
pin 8: 4.96
pin 9: 3.68
pin 10: 1.823
pin 11: 0
pin 12: 4.46
pin 13: 5.44
pin 14: 0
pin 15: 0
pin 16: 5.43
pin 17: 12~13
pin 18: 4.99

Non Working
pin 1: 4.98
pin 2: 0
pin 3: 4.2
pin 4: 4.66
pin 5: 4.98
pin 6: 0
pin 7: 0
pin 8: 4.96
pin 9: 3.65
pin 10: 1.823
pin 11: 0
pin 12: 4.47
pin 13: 5.35
pin 14: 12.25
pin 15: 0
pin 16: 5.51
pin 17: 12.68
pin 18: 4.98
 
The voltages are essentially identical except for pin 14. I think it was also ~12v when you took the readings for the non-working list. Without the voltage on pin 14, pins 13 and 16 couldn't have output.

If the rest of the voltages are accurate, there may be a bad connection between the 3526 and the driver transformer. Resolder the connections on the driver FETs (near the 3526) and the driver transformer. If those don't solve the problem, the regulator control module could be the problem.
 
The regulator module isn't available. You'd have to send the amp to TIPS to have the module replaced ($150).

You need to re-check pin 14 when the amp is not working properly to determine whether it has voltage or not.

If you want to 'bypass' the black box (regulator module), pull the regulator transistor (under the board) and replace it with a 120 ohm 1 watt (or larger) resistor (see image below). This will allow all of the circuits to function except the regulator. The amp will not produce full power but if both channels play normally and the amp doesn't cut off, you can be relatively certain that the reg module is the problem.


http://bcae1.com/temp/IMG_2840b.jpg