Behringer 180W bias setting

[schraedertr]

Hi,
I'm feeling smug, my Behringer replacement parts came in. Let's see, 2008 was a leap year so it was only 364 days from first inquiry until they said they arrived.

Anyway, I have a replacement LPA1180 board for my bass amp. It came without the 270 ohm 5 watt resistors, so I took them from the old board. There is a pair of what I assume are test terminals labeled X1 near one of the output transistors. I'm assuming I need to monitor X1 voltage while setting the trim pot.

As I am not an authorized Behringer repair center, I'm not privy to details like this. Can anyone tell me what I should be reading on X1, or even if that is the way to set the trim pot?

Thanks,

[Enzo]

There should be a 0.1 ohm resistor between those test points. You set the bias control for 5mv across them. Do this with the amp cold. if it was set a little cooler even, i doubt you'd hear the difference.

Bias adjust is VR1.

If I recall, on that board, don;t you have to remove the two resistors to get at the mounting screw for the transistors?

[schraedertr]

Enzo,
Thanks for the information. Yes, the resistors are in the way of one the voltage regulator clip mounting screws.

[Whammo!]

Hi,
I'm feeling smug, my Behringer replacement parts came in. Let's see, 2008 was a leap year so it was only 364 days from first inquiry until they said they arrived.

Anyway, I have a replacement LPA1180 board for my bass amp. It came without the 270 ohm 5 watt resistors, so I took them from the old board. There is a pair of what I assume are test terminals labeled X1 near one of the output transistors. I'm assuming I need to monitor X1 voltage while setting the trim pot.

As I am not an authorized Behringer repair center, I'm not privy to details like this. Can anyone tell me what I should be reading on X1, or even if that is the way to set the trim pot?

Thanks,

Tom,

I have the same amp with issues. All I get is DC in the speaker cone. Where did you order this LBA1180 board from and how much did you pay? I see no visible damage and my troubleshooting skills are weak.

TIA!

[schraedertr]

I got it from Audio Labs of Georgia. I've found them to be a good source of some of the harder to find parts. Note that it did take a year for the parts to come in!

If the board isn't burnt, which was my main problem, pull the output transistors and driver transistors and test them. DC on the output is a classic sign of shorted output transistors.

Tom