Bonus Points: The 2 pin header test points for biasing should be set to 30mv using the trimmer pot for each channel. There is a line of filled through-holes on the circuit board that are test points for all voltages Sometimes the ribbon cable causes strange problems and simply unplugging and reconnecting fixes these intermittent problems. There are two convenient larger unused through-holes next to R10 that you can use. Mackie products have been making music across a wide-range of applications since our founding in Woodinville, WA in 1988. De-soldering R10 from +64V rail is difficult due to heat absorption. R10 replacement can be soldered to underside if you do not have the tools to remove it. Screw the replacement Q15 to the heat sink before you solder it You need a small Torx screw driver to remove screw holding Q15 to heat sink R10 (A 10ohm through hole resistor that feeds Q15) is open (+64V on one side and 0V on the other. All DC power rails can be read by multimeter except the +16V (it is at 0V) No audio passes through the amp as the HOT Status activates the Muting Circuit HOT LED on the front panel remains lit, even after a cold start. Here is a website I just made to help others: I have also tested all transistors and diodes that I can access with a DMM, across both pre and power amp boards and none are shorted.I could not find much online for this M-800 problem but it also seems to have affected the M-1400 big brother. Maybe a grounding issue? I cannot seem to find this fault. After then screwing the board back onto the chassis, powering it on, the voltages fluctuate again. This comes with a 90 day warranty against manufacturer defects. This amp is 120v but can modified to 240v by removing the jumper (see pictures). I wiggled everything that wiggles on this board and cannot replicate the problem when the board isn't mounted. Brand New Genuine Mackie SRM450 Complete Amplifier V2. Six outputs each feature dedicated level control, mute, polarity invert, high/low-pass filters, 7-band parametric/shelving EQ, 600ms delay and limiting. I cannot seem to find any loose connections on this board. The Mackie SP260 2圆 Speaker Processor offers sophisticated EQ, crossover, dynamics processing and system protection, providing complete system optimization. Mackie may be silly cheap now because theyre old and obsolete, but old and obsolete is not the best credentials for power amps. So more bang for weight, bang for power draw, and bang for buck all else equal. Interestingly enough, when I unscrewed the pre-amp board and pulled it away from the chassis to test, I tried to power it on and the power supply then became stable. RMX 2450 is more efficient amp topology (Class G/H vs Mackie class A/B), and 2450 is a bunch more power. 11 plugged in, pre-amp board) All voltages start fluctuating as power supply goes into failure mode. 3 plugged in, Power amp board only) All voltages remain the same. Power supply rails (power supply disconnected from all other boards) +28 V measured +29.3 V -28 V measured -29.3 V +15 V measured 14.2 V -15 V measured -14.2 V +3.3 V measured +3.2V Should I be concerned with +-15 V rail being low at +-14V? Power supply rails (with conn. I am kind of going in circles on this trying to figure out what is wrong here. Any suggestions on how to proceed would be greatly appreciated! Thank you for anyone who can help!Īfter a very busy couple of months, I have finally returned to try and repair this speaker's amp. Unfortunatly, I do not have much in the way of test equipment, only a DMM. There is nothing obviously damaged and many surface mount components. I'm not sure what to suspect on this pre-amp board. Finally disconnected the pre-amp board and the rails all became solid with correct voltage levels. Then disconnecting the amplifier board, supply still fluctuating. I checked the +- 28V, +-15V and 3.3V with the all other boards connected, and supply is still fluctuates. Bad news the LED that indicates the unit is powered on lights up but then dims almost to off, then back on periodically. Good news was the amp now powered on (and didn't blow up the new parts). The final amplifier chip (TDA7294) as well as the resistor on its output were damaged. After opening her up and referring to the schematic I found a few burnt components and replaced them. The original fault was that the unit would not power on. I am attempting to repair a Mackie (TH-15A) powered speaker's amplifier.
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