QSC powerlight 1.8 issue

[ziggy007]

G'day Guys,

I have a QSC 1.8 Powerlight here that is frying a cap on the +ve voltage rail. The diodes and resistors in that line chk ok. Nothing obviously burnt out anywhere. I replaced the cap (470u 63v) as a shotgun but she smoked straight away.

My issue is the amp schematic that I have is worlds apart from what I am seeing on this board. The PS is connected differently & most of the component numbers/values don't match up etc.

I've got the official Service manual and the local Dealer confirmed that's what they have. Has anyone familiar with these amps seen this manual difference issue?

Unfortunately I don't have the time (and I'll begrudgingly admit), the Solid state Trouble shooting skills to make this worth my time to chase without an accurate schematic. I'd Hate to see this thing as unrepairable thou. The local guys say they don't repair these anymore. Thought Id try last ditch here to try and see if i can beat it.

cheers Gav

[nosaj]

See if there is a short to ground on that rail somewhere.

nosaj

[Enzo]

You need the right schematic. Look on your serial number label. Does it say anything like Powerlite 1.8A or version II or anything to indicate a revision?


What is the immediate cause of the cap failure? WHat voltage is being put on it? And is the polarity reversed or the cap in backwards?

[nickb]

What is the reference designator e.g C100?

A cap will blow due to excessive current. Likely causes are excessive voltage, AC applied instead of DC, incorrect polarity. Are you certain that you got the polarity correct? If it's in the switched mode power supply test for a shorted diode or inductor. I note the power supply uses two caps in parallel so if one it toasted I expect it's sibling will also be bad.

[Jazz P Bass]

This PL 2.4MB schematic may be a better match.

Or this one: PL 1.6HV

[Jazz P Bass]

Seeing that the OP did not post the PL 1.8 power supply schematic, here it is:

[ziggy007]

Gday all, Thx for replies, (sorry for tardy reply, been busy with a plethora of guitars for an upcoming show.)

* It is a 1.8 rev E main board PN WP000152-00 (sorry I should've posted the schem I had)
* I hadn't touched anything, it was arcing between neg and pos rails pcb tracks under caps C720 and C734 (470u/63v). The schems show C720 as a .1/250v poly
* The other models are still different again although some components are now correct, some now different.

I've taken out the 4 caps on that supply rail and when I bring it up on the variac, the main 240v fuse on the PS shows there is an obvious short somewhere as it heats and bends at only a few volts. I'm off to pull the BR and the 2 Fets ( Q701/702 ; they are correct numbering) on the pri side of the PS to try and isolate the short.
cheers
Gav

[ziggy007]

The BR chks ok but both IRGPc50u's are totally shorted. Not easy to source here in Australia by the looks. Has anyone used the Chinese ones off ebay? Otherwise its get flogged in postage costs from the states!
cheers

[Enzo]

I have no stories about those specific parts from some specific ebay supplier. But we have an endless supply of stories about fake parts from China sold on ebay.