Yamaha Stagepas 500 startup-protection fix

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Yamaha Stagepas 500 startup-protection fix

Unread post by custom_elect »

I have seen problems with the Stagepas 500 going immediately into protection/shutdown when they power up, and this post is what I did to fix this.

Note, this problem is not related to over-driving the amps and the unit going into thermal protection after a while, but this is turning the unit on and it immediately going into shutdown, then when left on for some time power-cycling and working as normal.

These problems were seen doing outdoor, evening, waterside, beach gigs in high humidity.

What happens is the hot humid air getting pulled through the unit to ventilate the power amps and power supply, condenses on the mixer front plate, notably around the fan metalwork.
This fan is directly next to the power amp modules and the module that has the DC protection circuit on.
When you pack up and especially if you put the speakers face down (i.e. mixer knobs upwards) in your car/van etc. this water drips down onto the power amp modules and leaves them damp.
(You can see that happens by the developments of rust patches on the internal fan metalwork).
The next day when you get the PA out for your next gig, when you turn it on, the DC protection circuit, senses there is DC present on one or more of the amp outputs and puts it into shutdown to protect the speakers and itself.
If you leave it on for a while, it eventually dries out and will start up properly after power-cycling. The dry out time taking anything from 10-30 minutes typically.

These are the things you can do to stop this happening:

1) When you pack up, put the speaker with the mixer in knobs-down/speaker-upwards, in your bag, car, van etc.. so that the moisture drips downwards and out of the unit (and not onto its power-amp modules).

2) When you get home, preferably don't leave the PA out in your car in the damp air again, but bring it in with you.

3) If you want to go even further:
Have a qualified tech dismantle the unit as per the service manual and spray the two power amp module PCB's and the controller PCB they plug into, with conformal coating for moisture protection (obviously masking the connectors and trim pot first).
After letting it dry for a few hours, the bias trim pot on each amp will need to be adjusted (as per service manual) before being completely re-assembled.

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Re: Yamaha Stagepas 500 startup-protection fix

Unread post by Buzzard »

Thanks, this might be very useful for Stagepass users ............ and ....

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Re: Yamaha Stagepas 500 startup-protection fix

Unread post by hallabing »

Hi there, James from England here.

That's an amazingly helpful post - thanks! Ours was doing that yesterday just before an NHS charity gig, luckily kicked in for the gig then gave up again during a playlist after. I stripped it last night - it looked super complicated so I put it back together. Read custom-elec's post about water getting in this morning.

I can't vouch for this being the best way to do it, but I blasted it with my wife's hairdryer for 3-4 mins through the fan and happy days it works again! :dance:

Had rung the service centre and I've saved at least £50 already - hurray for this forum!

Thanks again,

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