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 The SG3526 is obsolete, still available from digikey for $7 though.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.

 

[Perry Babin]

Try it without replacing R34 first. If it doesn't start, try replacing R34. Post what you find. It may help someone else.

 

[brandes.cm]

After replacing the SG3526 with a UC3526 the controller started fine, didn't touch R34. I had output coming from the IC. The down side, the bulk caps are all leaky. That I believe to be the original failure for this amp. The electolytic from the caps was all over the board, I didn't realize it before. I do now after I powered it up and see arcing. Time to order some caps!

cory

 

[brandes.cm]

Is there any reason to replace the primary side caps if the secondary caps have failed?

 

[Perry Babin]

I wouldn't replace them. If there isn't any adhesive between the primary filter capacitors, twist them to see if any have broken legs. If not, apply a tiny bit of adhesive to the tops of the capacitors to hold them together and to prevent the leads from breaking in the future.

 

[brandes.cm]

Thanks, I will do that.

Side note: working on a 501BD, newer version from 2003 I noticed it's using the UC3526 IC as well. I haven't checked the value of R34, but it seems RF switched to this driver IC on later designs.

 

[Perry Babin]

I think the MSI version of the 3526 are generally the ones that cause the problems. The rest may be OK.

 

[brandes.cm]

Got around to installing this amp in my boat and I have a weird problem. When I attach remote power my antenna reception degrades. Could this be caused from the ground shield on the rca's being open or maybe the 1K resistor is messed up tying gnd to ignd?

 

[amc32]

Poor reception? AM or FM? If AM it may be default of PWM

 

[Perry Babin]

It could be RFI from the class D section of the amp.

If the antenna isn't permanently mounted, try moving it away from the amp. If that doesn't help, check the shield on the antenna to confirm that it's intact.

Also confirm that you read 0 ohms from the ground terminal of the amp to the heatsink of the amp.

 

[brandes.cm]

I will check those tonight. Thanks again