Yamaha StagePas300

That is the 500 has an inverted channel, 300 is nomal, circuits etc on eservice for both. the 300 PA units are , AFAICS, the same as the 500 including overlay numbers just scaled component ratings , detailed in that manual. As it happens moving from bench testing a 300 PA to powering properly in the chassis. Check the state of the fans while at it, see thread a week ago "white coating ..."

Beware of topside solder (double sided board) of drain of Q7109 , crosslink to Q7103 , both powerFET. Have to remove large C2124 rather than removing the 30uH to get to that solder point R3114 , not labelled on overlay of the 300 is 1K , not 470R as the 500

Yes, I said that.

But particularly metal right angle jacks that are almost bound to end in disaster.

Gareth.

Ah thanks Gareth, I checked the circuit diag and yes the two amps are 'out of phase' I`ve been asked a couple of times to make short link cables with right angled jacks for the 'docked' amp to its own speaker. I`ll have to warn customers in future.

Ron

I don't quite understand how such designs ever make it to production.

Gareth.

Probably because they aren't designed by the people who use and abuse them.

Ron

Assuming everyone has the eservice schema to hand. Where exactly is the inverter in one ch of the 300 ? , I can see it in the 500 circuits

I've just noticed it written vertically at the amps . I thought the plug in amps themselves were identical. Taking a closer look one is marked LF

6479e-01 and the other b instead of e, will have to look at the SM as otherwise physically look the same. Just as well I marked where each came from as I thiought they were interchangeable. But then as long as an "unmatched" pair then would it matter which way round, assuming the ERR line worked correctly

I don't own a blink comparator, an app tacked onto a graphics package for astronomy or anything?

Cannot see any extra transistor on either 300 amp. Cannot see any different component Cannot spy any trace swapping at Q7119 / 7120, where else to look for phase swapping ? no other change of wiring seen or via pattern on the less populated side. Perhaps its under that white covering, only removed on the amp I've repaired.

I also now have seen the change of arrow associated with the 300 output jacks presumably indicating inversion also. You have to keep your wits about you in this game for such bear traps

Because its Yamaha? On some EMX I've disassembled to trace down an immediate shut down problem I've been searching for 30 mins for a ground connection between PSU/ PA/speaker ground to the mixer circuit ground. Finally found it: one single M3 screw between the speakons connects the power ground to the back plate, the backplate itself is connected to the sheet metal shielding when assembled correctly and this is then connected to mixer and preamp ground. When the screw or the shielding comes loose, the PAs offset will grow and shut down.