Oh Shoot! Did I Kill a Channel?

[techbiker]

Tauro,

Here is an update. I have been checking the channel 1 output board because I have been receiving some weird data from it. Here is a copy of the email that I sent Crown support regarding this issue:

Kevin,


Thanks for the schematic, however I think that there is some damage somewhere else in the amplifier... namely the channel 1 output board. Whenever I turn on the amplifier, the voltage of resistor R31 always jumps to around 500-550mv and static is emitted from the channel. When this happens, DC offset jumps to .300mv on the channel.

After the amp is turned on, I can adjust R26 so that the voltage of R31 decreases to around 310 mv, however the voltage across R31 always increases after a power cycle. Note that when I adjust R26 so that R31 is in spec, the static through the channel goes away.


The voltage of resistor R31 on channel 2 never changes whenever I "reboot" the amp. Neither does R32 on either channel.


Channel 2 has never exhibited any weird activity.


Could this be a problem on the output board? I wonder if bridging c153, r194, and c146 incorrectly could have resulted in a voltage spike that killed something on the output board? I'm fairly confident that everything is ok in the area of c153 on the input board.


Thanks,


Dallas

Do you think that I could have damaged something on the output board?

Thanks

 

[tauro0221]

Hi,
The two schematic are the same. I do not see any differences. I still think that you need to make sure that all the pins traces connections are OKAY. If I were you I will test all the pins traces in the UC104 are connected to all the components for each pin. Maybe other experts have a better idea than mine.

 

[techbiker]

Tauro,

Thanks for all of the help but I am afraid that I toasted this great amp. I spoke with Crown support and it was recommended that I turn the input board 180 degrees and swap the output channels in order to see if the output board for channel 1 was bad.

Initially, I plugged in everything correctly, however when I turned on the amp, the fan turned on 100% and the ioc lights stayed lit. It appeared that I had plugged in 2 of the connectors the wrong way so I reversed them. Then, I smelled burning electronics and saw a few resistors burn up on the input board.

I guess that there was another problem with the channel 1 output board initially (that was why the ioc lights stayed on). Reversing the plugs sent 45 volts of power back into the input board and burned up a few resistors...

Anyway, I guess that it's time to cut my losses and move on. I have a malfunctioning Com-tech 400 coming in that needs to be repaired. Hopefully, I can use some of the parts from this one and resurrect it. Thanks again.