Yamaha powered mixer, need help troubleshooting

[netwerx1]

I have a Yamaha EMX5016CF that I'm trying to get operational. It wouldn't power on at all, and we found a couple of resistors that were open on the power supply board. After replacing those, the unit will power on for about 3 seconds, then shut off. It appears a relay is opening at the time it's shutting off. We can unplug it and plug it back in, and it will again turn on for 3 seconds, then off. I do have the service manual, but it doesn't give me any guidance for this. We followed the steps in troubleshooting the PS board, and all of the components it told us to check seemed to check out okay.

What would be some possible next steps for troubleshooting this problem?

[Jazz P Bass]

Yamaha SMPS

I believe Yamaha used a Switch Mode Power Supply in these units.
You may have gotten the power supply working, but it is going into protect.
Here is the schematic for EMX 5000 series power supply.
If I remember correctly, that click is when the power supply turns full on.
Ypu could try it without the amplifier connected.
Hook up a 2K dummy load to the + & - power rails.

[Enzo]

Which resistors were open, and did you determine why?

Disconnect the power amps from the power supply. Does the thing power up OK as just a mixer?

Until the unit will come on and stay on, do not connect any speaker loads. If you have been loaded, take them off adn see if it will power up.

[Brad1]

If you have been loaded, take them off adn see if it will power up.

Bad advice, Enzo. Really shouldn't work on things when you've been loaded.

Brad1

[Enzo]

I ordered one of those loaded potatoes at the restaurant the other day, the waitress brought my wife a drink.


Or...


When I get drunk I imagine all the women are naked. You might say I get loaded for bare.


Or...

I got arrested for drunk and disorderly. I've heard of locked and loaded, but this is my first time for loaded and locked.



Nah, I'm losing it... better stop.

[netwerx1]

UPDATE

Thanks for all the replies, we got it working. From what I understand, the blown resistors were current-limiting resistors that were on the front-end of the power circuit. We replaced those and then had the 3-second power up like I mentioned. Well, apparently there is a sensor or interlock for the top panel...we had everything connected, but the panel wasn't in place. Makes complete sense now, but without the top panel, the airflow isn't drawn through the components as designed. So once we put the panel in place, it came on and stayed on.

I ran it over the weekend, with speaker loads attached, and everything is working great, both internal amps are operating fully. This was a non-operational unit that I purchased at a significant (75%) discount, with the thought that I could fix it and end up with a great bargain. It was a risk, but it panned out!

Thanks again