marshall valvestate 80, model 8080, 80 watt, dead.

[gjcruz]

my marshall 8080 is dead. don't know what's gone wrong. changed power supply cord, same result-still nothing. fuse is good. power switch is good. don't know if main transformer is shot. what are the voltages i should be reading at all terminals (3 on one side: white, black, white; 4 on other side: top to bottom: red, yellow, orange, and purple)? i must admit my amp had been sitting near a very humid area. would like some help here if anyone would like to, i would really appreciate it.

[Jazz P Bass]

Marshall Valvestate

Here is the schematic.
If the amp is popping the main fuse, something is shorted.
I would suspect the output transistors.

[gjcruz]

dead marshall

thanks for your reply. but the problem i have is that the amp is turning on when the switch is on. swapped power cord to rule out a bad cord, but same result-no lights, no sound, as if it wasn't even plugged to the wall outlet. also the fuse is good wasn't blown. with meter working from power supply everything is checking out up to the main transformer. there, is where i would like to know what the voltages are on all legs (both sides) of the transformer. i have some voltages but not sure what they are. should there be a voltage reading on "other" side (white, black, white wires) regardles of voltage from side with red, yellow, orange, and purple wires? please forgive my ignorance on the lingo. not sure which is the input, output, or primary or secondary. but thanks for your reply.

[Enzo]

I have no idea what color each wire is.

Follow the mains power from the power cord, through the fuse and power switch, and eventually it comes to the transformer. That is the primary side. It must have whatever your mains voltage is. If no mains voltage there, then nothing will work.

The low voltage side of the transformer is the secondary. Those wires go directly to the main bridge rectifier. I don't know what voltage they are, It will be something like 20-30VDC on either wide, or from wire to wire about 40-60VAC. It is not going to be wrong, it will either be there or be missing.

You will almost always find some small AC voltage reading, remember you can grab your meter probe tip in your fingers and get a reading.

[gjcruz]

"She's Alive...The Marshall is Alive!!!

@enzo, followed my way back from power supply connection to transformer primary. kept getting weird readings with ohm meter. seem like i was getting half values. but was getting some voltage to primary. long story short, turned out to be the power switch. marshall uses a switch with two sets of contactors inside. well one of the two set had dropped out of position and was not making contact. the other set, however was which was only giving some voltage. either way thank the Lord for this since this is our chruch amp and really needed it to work by this sunday. and thanks to you guy that replied with your suggestion, all were very helpful. thank you all very much and the Lord bless you all. GJC of Christian Family Fellowship (Pastor)