Marshall Mode 4 (mf-350) IC's blowing up

[clydey]

thanks for that cheers

[pablocarrillo]

it`s working again!!!

Ok; thanks to all; the amp itīs now ok again; new ic`s and resoldered a shorted and fulminated copper wire of the pcb.

some pics:

marshall mode four Photo Gallery - Photo 5 of 23 by pablo - MySpace Photos


marshall mode four Photo Gallery - Photo 6 of 23 by pablo - MySpace Photos


marshall mode four Photo Gallery - Photo 7 of 23 by pablo - MySpace Photos


marshall mode four Photo Gallery - Photo 8 of 23 by pablo - MySpace Photos


and this appears behind the big pcb:

marshall mode four Photo Gallery - Photo 20 of 23 by pablo - MySpace Photos


marshall mode four Photo Gallery - Photo 21 of 23 by pablo - MySpace Photos

fixed out:

marshall mode four Photo Gallery - Photo 22 of 23 by pablo - MySpace Photos


and finally those were the ic`s that the amp had when came to me.


marshall mode four Photo Gallery - Photo 23 of 23 by pablo - MySpace Photos



Finally i wanted to thank you so much to all people that helps me on service this amp; thanks to these people; I don`t broke any 7293!!!

Yeahh; finally trow away this dificult amp to his owner!!!

[ninetynineblackcats]

Marshall Mode Four TDA7293 Replacement

What would happen if a person replaced the four TDA7293's and then connected a speaker cabinet and powered up the amp? I assume it would be OK if there were no other issues with the amp? Is this correct?

[ninetynineblackcats]

MF350 fuse size

I can't read the fuse size inside the amp. There is glue covering it. Does anyone know the proper size?
Thanks.

[pablocarrillo]

4 Amperes 250 V for european units

[ninetynineblackcats]

mine is a US model running on 120AC. I think it requires an 8 amp fuse but not sure.
Thanks.

[Mike.K]

Schematics

Hello,
I have probably the similar troubles with my MF 350 as the other guys here I gues (or it's just f.....up anyways) ..there is something wrong with OD1 and OD2 mode - both channels are too noisy even when the guitar is not played (just connected to an amp and switched to one of the modes). The noise sounds like a “heavy feedback” especially at the higher level of gain and volume and is actually almost louder than the sound of own guitar. I have tried to change the valves for the new ones but the noise was still the same as before so it need's to be repaired somehow.. do you think you could post here a rest of the schematic please? I wrote to a technical support of Marshall if they could possibly send me some service manual but haven't got any answer yet. A friend of mine is about fixing the problem with my MF but there aren't many things he can do without schematics.

Thanks a lot
Michal

Please take easy my English - not a native

[J M Fahey]

ŋNoisy/feedback with high gain? Itīs probably normal.
What if all guitar controls are set on "0"?
Still hissy, but does it still feed back?

[Enzo]

And if it really is a problem, my first thought is a noisy op amp.

[Mike.K]

ok, I tried to set all the guitar controls to zero, MF's master volume to 2 pm and the result was that OD1 sound pretty good without hiss and OD2 was extremely hissy. I turned up the volume on my guitar and OD2 became immediately noisy.. unplayable

[Mike.K]

Thank you Enzo.. when I get schematics I will tell about op amp to friend of mine

[iccaros]

not to hijack the thread, but does anyone have the full schematic. I have a MF350 I have had for over 10 years, and it has had zero problems, well once in the studio the engineer unplugged the cab while I was playing.. Stupid @#$#.. in any case.. I know the pain of fixing these. But no other issues.
what I want to do is build a EL34 PP and use the preamp section with it. I have tested it with the line out, and I can say the amp sound better in some cases, more touch sensitive. I get get a used MF350 cheap so modding the entire thing, while keeping mine in good order would be the way to go.

regard less of how much a of pain this amp can be, it might just be how I play, but I get complement on my sound at every show I do. Some engineers who keep telling me this is a crap amp that can not get a good sound take it back when I bring my amp in, unless they are expecting it to sound like a JCM 800, which is just ignorance.

thanks for any help and I fixed mine by just reading Enzo's (thanks you have saved my A$$ more than once with out knowing it) comments in the past. The ground issues is a big deal and replace all of the power out chips on once.

[Enzo]

Here.

[Enzo]

How odd, of my four attachments, two came up as thumbnails and two as links. All four pages are there though.

[iccaros]

How odd, of my four attachments, two came up as thumbnails and two as links. All four pages are there though.

Thank you, now To the plotter to make these a size I can trace through them