I have never seen one of these amps before, but guts wise I am pretty much staring down the barrel of an MTX 81000D, or a variant thereof.
Anyway, This one is stuck in shut-down. All the outputs, and etc test ok. the rails come up, I have +/-18V at the op-amps, and I have 20v at both A3120 opto-drivers.
But the class-D indicator LED doesnt light, and no output. It does appear that some water damage, or something fell inside the amplifier at one point, because I see some copper blown off near the end of one of the current sense bus-bars near the rail filter caps. Its still connected to the circuit though, and the output transistors are not damaged.
so my immidiate thought from that point is test the transistors that are coupled to those sense bars, and they are ok, along with their traces.
any ideas? Looking for the Q240 protection transistor, but it doesnt appear to have one on this design.
Anyway, This one is stuck in shut-down. All the outputs, and etc test ok. the rails come up, I have +/-18V at the op-amps, and I have 20v at both A3120 opto-drivers.
But the class-D indicator LED doesnt light, and no output. It does appear that some water damage, or something fell inside the amplifier at one point, because I see some copper blown off near the end of one of the current sense bus-bars near the rail filter caps. Its still connected to the circuit though, and the output transistors are not damaged.
so my immidiate thought from that point is test the transistors that are coupled to those sense bars, and they are ok, along with their traces.
any ideas? Looking for the Q240 protection transistor, but it doesnt appear to have one on this design.
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I took my reference measurement again at the RCA ground on the meter, instead of chassis ground. and the +/-18v is good at that point, but still wrong at main amp chassis ground.
So today I decided to scope across the two 430 ohm parallel resistors that connect the RCA ground (ground for +/-18V) and main amp ground.
It has DC that is swinging from +6v to -6v back to +6v. this cycle repeats about 1Hz. maybe a little bit slower.
so its swinging from +/-6v at 1Hz.
???
So today I decided to scope across the two 430 ohm parallel resistors that connect the RCA ground (ground for +/-18V) and main amp ground.
It has DC that is swinging from +6v to -6v back to +6v. this cycle repeats about 1Hz. maybe a little bit slower.
so its swinging from +/-6v at 1Hz.
???
How can you tell if the class-d saction wasn't comeing on?? I have the same amp. it power up just fine, But no sound. I have three red leds that are on. Two are located in front of the off the big capacitors (led406 and led407) the other led is located in the left top coner just across from the out put capacitors (led 236).
the red LED in the upper left corner wasnt on. If its on, the amplifier is running.
But you may not have sound if none of the crossover resistor packs, and jumpers, etc.. are in the right places or missing. These things are notorious for that, a low-pass, or high pass jumper is 1 pin off, or is missing, you wont get sound.
If that appears fine, then you need to check the op-amp +/-15V but my guess its probably fine because it also feeds the comparator for the class D output stage.
But you may not have sound if none of the crossover resistor packs, and jumpers, etc.. are in the right places or missing. These things are notorious for that, a low-pass, or high pass jumper is 1 pin off, or is missing, you wont get sound.
If that appears fine, then you need to check the op-amp +/-15V but my guess its probably fine because it also feeds the comparator for the class D output stage.
check everything out. looks to be good I replace the 3845a driver and r174 and r175 burned up in the crossover section. any ideas? also the red led light on the amp kind dims when I had the rca plug in the once I unplug the rca the led stay on very dim. the top left led is the one im referring to.
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