Gallien-Krueger MB150S III resistor values

[Lifto]

Hi all,

A friend of mine has a Gallien-Krueger MB150s-III which has 2 burned resistors. I'm having problems identifying the orginal values of the resistors. The colour codes aren't visible anymore. The codes bellow the parts read R508 and R509. I found 2 schematics (a poweramp and preamp schematic) but the parts mentioned in these documents do not match the codes found on the board.
I found the following schematics:
GallienKrueger M150SIII Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics (preamp)
GallienKrueger M150SeIII Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics (poweramp)

Does anyone have a idea what the values should be or how I can find out?

Pictures (the burned resistors are located on the right side of the board):

[Enzo]

You have the older SMPS, they replaced it with a linear supply and do not support the switcher. But they ought to still have the proper schematic.

With those two burnt up, you VERY likely have bad switching MOSFETs as well as a bad Q515, and probably the IC too.

CALL G-K and ask if they can provide the schematic for the old switching power supply from this series. I found it in the old ML series drawings for one place.

[Lifto]

Thanks for the fast reply! I will contact G-K and see if they can supply me with the correct schematic.

[Jazz P Bass]

I am not too sure that you read Enzo's response.

This is a Switch Mode Power Supply.

And it has failed.

If you have never worked on an SMPS, you must be aware that they are dangerous to work on.

Replacing the resistors is Not going to fix this thing.

[Lifto]

Thanks for the warning. I respect the knowledge you and Enzo have and if you say it won't be an easy fix then I'll refrain from working on this unit. I rather stick with simple tube amps.