Dead Marshall MG100

[52 Bill]

Do the headphones still work ok? If they do, I'd focus on the headphone jack.

Plugging into the headphone jack turns off the speaker. If the switch contact on the headphone jack isn't closing, the speaker will not work. Make sure that the jack is not loose and has not come unsoldered from the pc board. Visually inspect the silver metal leaf contacts (if they are visible) to see that they are not bent and that they are making good contact. You can check the closing of the contacts with your ohmmeter.

If the top of the jack is open, you can push down on the leaf contacts with an insulated tool (chopstick) while the amp is playing and see if sound is restored. Of course be careful if you run the amp out of the cabinet.

[cpuslave]

Alright well I put everything back together and turned it on (with the chassis out) and it powered up fine. Still no noise whatsoever. Then after about a minute it started to smell shitty, and right where I'm pointing, it was rediculously hot and started to smoke a bit. The smell was there before when it initially blew on me.

What is that piece right there? And what should my next step be?

[cpuslave]

Okay so I'm still havin problems. Never had this fixed actually, just had some other priorities to attend to, but now I need to get this fixed more than ever!

Situation: My Marshall MG100DFX (combo) doesn't produce any sound. I plug it in and it turns on fine (LED, fan come on) but it doesn't produce any sound through the speaker. I plugged the speaker lead into the headphone jack of a 10watt Marshall I have, and there's sound for sure. I've tested the fuse and sprayed some canned air and electronics cleaner just about everywhere imaginable. I've scanned both sides of the bord for any noticeable burn marks or weak solder joints but couldn't find anything. I'm at a standstill here guys. Help me out?

[cpuslave]

BUMP

Also, the voltage regulator (I think that's what it is, it's what I'm pointing to in the picture a few posts above) stinks like it's burning everytime it's powered up.

[Gtr_tech]

BUMP

Also, the voltage regulator (I think that's what it is, it's what I'm pointing to in the picture a few posts above) stinks like it's burning everytime it's powered up.

Thats not a voltage regulator, its the power transformer. Unplug the pwr amp IC board from the main board. Pwr it up and monitor the temp of the pwr transformer. Does it still get hot? Since it started to smoke I think its prob'ly toast. Either its got a partially shorted secondary or there was something loading it excessively (output IC?) and caused damage. You just may have a name brand doorstop on yer hands.....

[cpuslave]

Okay so I disconnected the 15-pin connector from the IC board and then powered it up. Still getting super hot and smelling like burnt electronics. I unplugged it after about 2 minutes.

[Gtr_tech]

Either theres something else loading the secondaries or the transformer has a bad winding. Disconnect all the secondary leads (mark them as to where they go on the board with the "J**" numbers). Leave the main power leads (primary, where the 117vac from the line cord comes in) hooked up. Power it up, wait, report back.

[cpuslave]

I'm going to assume the secondary leads are the 2 red, 2 blue, black, and brown leads protruding from underneath the blue wrapping.

I noticed while I was unplugging these that the corresponding colors were labeled on the board, and that I had a black wire where there was supposed to be a blue, and vice versa. I switched these out and powered it on then waited a few minutes. Here's some good news (I'm hoping)! There was no burning smell, no smoke, and the transformer didn't even get hot!

However, still no sound. Headphone jack still works too.

[cpuslave]

BUMP!

[cpuslave]

Anybody? Desperate times here!

[olddawg]

Have you checked to see if you have a shorted rectifier. Do you have a multimeter? Something is drawing major current from the PT secondary. Everytinme you turn it on you may be causing more damage. I would take some static checks with the amp unpluged looking for a dead short somewhere like a filter cap, rectifier, zener diode, or regulator if you have already floated the power amp.

[dimefan0908]

I'm going to assume the secondary leads are the 2 red, 2 blue, black, and brown leads protruding from underneath the blue wrapping.

I noticed while I was unplugging these that the corresponding colors were labeled on the board, and that I had a black wire where there was supposed to be a blue, and vice versa. I switched these out and powered it on then waited a few minutes. Here's some good news (I'm hoping)! There was no burning smell, no smoke, and the transformer didn't even get hot!

However, still no sound. Headphone jack still works too.

Hey is there any way you could send me the order you have them wires in? I cant seem to find the order any where. Thank you

[olddawg]

Hey is there any way you could send me the order you have them wires in? I cant seem to find the order any where. Thank you

You would not believe how many misprinted boards I have seen in my life. Many more misprints than mis-wiring from the factory, although I have seen my fair share of butcher jobs from nuckleheads too if someone has been into it previously. The most likely places are leads and connector being mirrored or flat out wrong. If I was you I would get a known good schematic and TRACE IT OUT. It just takes a minute and could save you a lot of grief.

[dimefan0908]

You would not believe how many misprinted boards I have seen in my life. Many more misprints than mis-wiring from the factory, although I have seen my fair share of butcher jobs from nuckleheads too if someone has been into it previously. The most likely places are leads and connector being mirrored or flat out wrong. If I was you I would get a known good schematic and TRACE IT OUT. It just takes a minute and could save you a lot of grief.

I have found the schematics that are from Marshall themselves. but its for the board and I have no idea on how to determine which wire goes where. I am a diesel mechanic with some knowledge on how to read schematics I also own and can use a multi-meter, but I figured if there were any honest do it yourselfers out there willing to, or already have their MG100 cracked open to maybe send me pictures of the power transformers wires and their corresponding spots on the board. Not likely but it would be nice right?