@AndrewMason, is there a way to make the amp automatically turn on when main power is turned on?
Hi
@pos
This modification to make the unit power on at startup is WARRANTY VOIDING and UNTESTED, but here it is if you want to be the first to experiment...
-Order some spares for U701 SN74HC109DR in case you need to undo this, or in case the rework messes it up.
-Gently remove U701 ideally with hot air tool, taking care not to rip any pads off the PCB. Ripping pads could be disastrous and irreversible. Don't proceed with this step unless you are confident in your rework skills.
-Cut or break off pin 6 from the U701 chip (i.e. clip the pin from the package. Leave the PCB alone)
-Re-solder U701 into place on all pins except the missing one U701.6.
-Solder a jumper wire or make a solder bridge from U701.7 to the pad where U701.6 used to connect.
This will make the amp use the 1Q* output of the chip instead of 1Q to control on/off state of everything. Once 24Vdc power is applied, it should start up.
If it doesn't work, remove all the mods and put a new chip in U701.