QSC K12.2 repair

[clintronics]

Symptoms: All 3 signal LEDs light up with the display and then cycles off about every 5 sec. What I found: F1 blown, Q16 shorted, D36, D20, D37, D29 D15 tested bad and all replaced. 15v rails 5v rails and 12 VLOW all there. But thing keeps cycling no difference. Im stumped. any advice?

[Enzo]

This came after I closed my QSC authorized shop/ Do you have the schematics for us? I have no idea what or where Q16 D36 and so on might be. You report your low voltage supplies are present, but you don't mention the main rails. Your description sounds to me like an SMPS trying to start. Two things cause that. One is a problem in the SMPS itself, and the other is excess load on it, most likely a shorted output transistor.

[The Dude]

Check this. I've seen several with this problem.

[clintronics]

Dude thats the K12 Im posting about the K12.2

[clintronics]

Here's a repair manual at this site. yes I have the big rails and all the OP mosfets test good. https://adjuntos.yoreparo.com/defaul...93137e1102.pdf

[clintronics]

This has nothing to do with MY repair but evidently this unit needs a firmware upgrade to prevent low end speaker damage. https://www.youtube.com/watch?v=wHKz8mU62x0&t=308s

[clintronics]

official firmware update from QSC https://www.qsc.com/solutions-produc...s/k2-firmware/

[izzzzzz6]

Check D51 under the PSU board. My problem is power constantly turning on and off. My other problem is that i do not know the diode type without the schematics. I have opened a case with QSC to see if they tell me but i doub't they will. I's marked KB but i do not know it's voltage ranges. KB is a general marking for some SMD zener diodes. I guess you can also check the slightly larger diodes squeezed between some caps on the top side. They tell you PAGES AND PAGES! of all these repair tips in the service manual but then tell you to go to the site for the schematics which i couldn't find.
Diode type for D51 anyone? Please.

[Jazz P Bass]

I cannot tell what circuit you are on.
If it is the SMPS, then D51 is a Schottky barrier rectifier.