Yamaha Stagepas 300 powered mixer, loud pop at shut off

[Randall]

Using pin 2 for Enable signal, and pin 4 for Gnd.

[Craciun]

Yamaha Stagepas 300 not turning on.

Hi Guys,

I have a Yamaha stagepas 300.

I had been using it for a number of hours at full volume and also driving a stagepas 150 as a monitor.

The whole amp blew and when i turned it on again smoke came out from the smaller of the two cooling fans.

Now when I turn it on, the leds flash and then the amplifier powers off, after around 20 secs the Leds flash again.

I replaced both cooling fans and it does the same thing, except when I power on the fans move slighly before the whole thing trips off.

Any Ideas?

[Jazz P Bass]

Using pin 2 for Enable signal, and pin 4 for Gnd.

Pin 4 is 'Signal Ground'.

Try Pin #3. 'Output Ground'.

[Randall]

Same results from gnd pin 3.

[Randall]

Please start a new thread for your question

[Jazz P Bass]

Hi Guys,

I have a Yamaha stagepas 300.

I had been using it for a number of hours at full volume and also driving a stagepas 150 as a monitor.

The whole amp blew and when i turned it on again smoke came out from the smaller of the two cooling fans.

Now when I turn it on, the leds flash and then the amplifier powers off, after around 20 secs the Leds flash again.

I replaced both cooling fans and it does the same thing, except when I power on the fans move slighly before the whole thing trips off.

Any Ideas?

It appears that you may have damaged output modules.

Good luck finding them, as I don't think that they are widely available any more.

[Jazz P Bass]

When turned on, voltage at the enable pin rises quickly to about 3.5 volts, then ramps down and snaps to about 25mV at about the two second mark. When powered off, it jumps down to about -3v at the sound of the pop, then continues to drop slowly to about -5v, then slowly rises to ground over the course of maybe 10 seconds.

From a look at the Philps UCD module, it appears that the Enable function happens when that pin is at zero volts.
(my initial assumption was incorrect)

The circuit inside the module is a PNP transistor.
So pulling the base low is what Enables the module.
So to mute it, the base should go high.
That is where I am confused, as to the -5Vdc reading.
Where is that voltage coming from?

UCD S200.pdf

[Jazz P Bass]

I had another thought.

Was the unit fully assembled when the 'pop' was heard?

Yamaha has a history of bizarre grounding where the unit must be fully assembled to achieve the full grounding connections.

The unit may not perform properly unless all connections are made. (ie: full & final assembly)

This can even affect voltage measurements.