JLM AUDIO

I have a 1290 Pre-Kit. I did not assemble it, it was built 6 or 7 years ago and last year the first channel stopped working.

Upon inspection the only noticeable issue was the 47 ohm resistor had been burnt out.

I have replaced this resistor but the channel has an issue of only putting out an audio signal sporadically.

The 47 ohm resistor is emitting much more heat than channel 2's 47 ohm resistor.

I am thinking this difference in heat could be an indication of what be wrong. I don't know this circuitry at all so I don't know what it might be hinting towards in terms of the issue.

I do not see any other component damage in channel 1. However comparing channel 1 to channel 2 I see subtle difference in brands of components, but I don't think brand should determine if the circuit works or not.

Channel 2 works fine.

I'll attach pictures:

orgnanoise wrote:I have a 1290 Pre-Kit. I did not assemble it, it was built 6 or 7 years ago and last year the first channel stopped working.

Upon inspection the only noticeable issue was the 47 ohm resistor had been burnt out.

I have replaced this resistor but the channel has an issue of only putting out an audio signal sporadically.

The 47 ohm resistor is emitting much more heat than channel 2's 47 ohm resistor.

I am thinking this difference in heat could be an indication of what be wrong. I don't know this circuitry at all so I don't know what it might be hinting towards in terms of the issue.

I do not see any other component damage in channel 1. However comparing channel 1 to channel 2 I see subtle difference in brands of components, but I don't think brand should determine if the circuit works or not.

Channel 2 works fine.

I'll attach pictures:

Let me know the voltages you measure before adjusting anything

OK first check you have 24vdc coming from the TREX to the 1290 module that is not shifting when measured to 0v?

Then check the voltage across the 12R 1W on the main pcb to check it is 1.4vdc?

If it is not 1.4v then adjusting the small trim pot on the output amp card to see if it can be set to 1.4vdc.

If it much higher than 1.4v the output card has had a failure or short.