BD1000 wont start up

[brandes.cm]

The amp won't start up. The shutdown pin is sitting low even with pins 1,2 and 13 lifted on the lm339. Not sure if it points to the SG3526 or not. Pin 8 of the SG to ground reads 11K, don't see that as an issue. Am I missing something obvious?

cory

[Perry Babin]

Post the voltage for all pins of the 3526.

IC#
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:

[brandes.cm]

IC#
Pin 1: 5.723
Pin 2: .379
Pin 3: .993
Pin 4: .993
Pin 5: .198
Pin 6: 0
Pin 7: 0
Pin 8: .983
Pin 9: 4.6
Pin 10: 2.35
Pin 11: 0
Pin 12: 5.9
Pin 13: .939
Pin 14: 15
Pin 15: 0
Pin 16: .88
Pin 17: 15
Pin 18: 5.914

[Perry Babin]

It may be due to one of the inputs of the 339. Post the voltage on it:

IC#
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:

[brandes.cm]

IC#
Pin 1: lifted
Pin 2: lifted
Pin 3: 15
Pin 4: .188
Pin 5: 2.365
Pin 6: 4.77
Pin 7: 5.922
Pin 8: 2.5
Pin 9: 5
Pin 10: 5.9
Pin 11: 9.1
Pin 12: 0
Pin 13: lifted
Pin 14: lifted

[brandes.cm]

Pulling pin 8 high causes the amp to start, but immediately blows my 15amp input fuse. Is the inrush current that high on these amps?

[Perry Babin]

With the outputs out of the circuit, the shutdown pin should be pulled high by the 20k resistor (R19?). If the resistor is within tolerance, it's possible that the IC has failed. The 5.9v on the 5.1v regulator output is well out of tolerance and often indicates that the IC has failed.

[brandes.cm]

Would the UC3526 be a good replacement? The SG3526 is obsolete, still available from digikey for $7 though. I will place a socket for ease of removal.

[Perry Babin]

It should be OK but I've had problems with other 3526s. If the supply doesn't start with the new IC but the voltages are more inline with what you'd expect, replace the 0 ohm jumper (R34) with a 1k ohm resistor.

[brandes.cm]

I will get them on order, should have them in a couple days.