SOLVED: Outboard PSU for Alesis 3630 backfeeding -15VDC to AC line

[Blue Jinn]

Alesis 3630 Adapter Ac 9V 830Ma on Amazon...​

I removed all the internal PSU components in favor of an outboard PSU. It seemed easier at the time as the modifications called for making upgrades to the onboard supply. the regulators also didn't have very stout heat sinks.

 

[ccaudle]

I think this is the telling data point:

It seemed to go away if the PSU board was left not grounded to the chassis box

I would recommend tracing out the connections on the power supply board, and specifically check what the connections labeled "chassis" connect in the circuit.

 

[Evertide]

Power supply.

Board has + 15 Volt , Ground and - 15 Volt.

The chassis should be connected to ground...

Check is a heat-sink is Life ( + or - 15 Volt ) and connected to the chassis...

 

[robovox]

Re Evertide's post #11: have you looked at the underside of the 3630's power switch? From your top-view photo, it looks like you're using a switch that is meant to turn a single 9VAC circuit on and off to switch both rails of your +/-15VDC.

Do your switch's PCB traces look like this?

 

[Evertide]

Safety note :

You are making from a class 2 a class 1 unit ; so as well the unit as the power supply should be grounded.

This means the metal housings should be connected to ground ( 0 Volt ) , so make sure there are no - 15 Volt connections ...

 

[Blue Jinn]

Re Evertide's post #11: have you looked at the underside of the 3630's power switch? From your top-view photo, it looks like you're using a switch that is meant to turn a single 9VAC circuit on and off to switch both rails of your +/-15VDC.

Do your switch's PCB traces look like this?

I cut the traces so it acts as a DPST switch.

 

[Blue Jinn]

Thank you to everyone that helped out. It looks like the problem was the cable, which had a broken pin on the positive side. I don't know why that caused the fault, but I'm waiting on connectors to fashion a new cable.

 

[Blue Jinn]

To close out, was a bad cable. Built new one, works great now.