Line 6 M9 power problem

[tyzjames]

Hi guys,

Hope this is the right place to post this. I have recently modded my Line 6 M9 and changed all the switches and also installing 2 expression switches at the top with LEDs. Everything works when I turn it on, but here's the problem. The power supply will fry and stop working after 5 min of running the M9. I have already fried 2 power supplies running this unit. The only circuit intrusive mod I did was to power the LEDs from the DC point on the circuit board (there a point labelled +DC near where the AC adapter is, providing 9v power) and then grounding it back to the ground point of the AC power input. I doubt that will cause any problem but just wondering. I have also checked the diodes around the AC jack and all seems to be working fine. In any case, if one diode is faulty, the AC power should just run to the ground and the M9 will not turn on at all, right?

If anyone has any clue do let me know!:) What a tricky fix, the only way to test a solution is to power on the unit and hope another power supply doesnt fry!:S

Cheers,
James

[Skrogh]

How exactly are the LEDs attached? did you remember the current-limiting resistor?
How are the "expression switches" mounted, how are they wired?

It sounds very much like you have a short somewhere. Next time you test it, keep your hand on the PSU, if it gets hot - quickly pull it out.

The point labeled "DC" at the power input is NOT regulated and might be closer to 12V than to 9V so bear that in mind.

[tyzjames]

thanks for the reply! Is there any way to test for a short circuit tho? If I use the multimeter to measure the current at the AC power jack, will it be the current that shows a much higher reading than usual?

[Skrogh]

It is very easy to test IF it is a short (or a near short)... But hard to find where it occurs. Besides Whats the gain of knowing it's a short, if you don't know where it is, or how to prevent it?

I would not recommend turning it on and burning off anymore PSUs. Besides I think you are quite lucky if the unit keeps taking all the "electrical beating" without dying.

If you pan on measuring the current with a multimeter, you will have to cut wires, to insert it in series with the conducting wires. Start off by checking that nothing shorts out against the chasis or exposed soldering pads inside.

[tyzjames]

Thanks for your advice, Skrogh.

The expression switches are are connected to the exp jacks on the M9, while the LEDs are connected to the +DC power source with 2.2k resistors. You're right, the +DC point is 12v, not 9v. I'll just try taping up all the joints to make sure there is no short circuit as it is a pretty tight fit with the switches. Hopefully that works!