#1
I have an old Marshall MGHDFX100 amp head that i would like to get working again so i could sell it/use it as a back up. I have a peavey 6505+ so dont just tell me i should get a new amp lol.

When i replace the fuse it instantly blows and the amp shuts off. I have an electricians multi-meter and am aware of the dangers of capacitors/ saftey procedures and playing around with an opened amp. How could i begin to trouble shoot what is causing the fuse to blow?

Its possible i damaged the amp by plugging it into the wrong cabinet.

Ive also heard that once the fan on these amps go, that could cause the fuse to blow. I have no way of checking to see if it works since i cant power the amp on for more than 1 second.

Also, am i getting the right fuses? i live in the USA and have 120v main voltage. The Amp says next to the fuse "115v 3.15al fuses. what does AL mean? I bought 120v 3.15a fuses and 250v 3.15 slow blow fuses. Could it be im using the wrong fuse?

Id appreciate any help/links you guys could give. Im reluctant to take it to a shop and have them charge me a third of what the amp is worth to fix it lol.
(signature removed, please choose another)
#2
After doing some research ive found i probably blew the output transformer. I have used the amp to record directly into an interface without having a speaker connected, from the line out of course.

Is there a way to safety check if the output transformer is the cause? i Guess when i was younger i unscrewed it to check and lost the screws that connect it to the chassis. could that also be an issue?

I dont think i would attempt to install a new one if that was indeed the problem, i would just like to know exactly what im getting into.
(signature removed, please choose another)
#4
^+1
No OT in a MG
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#5
Have you tried the slow blows in there in there yet? If not then I'd put my money on the fan, that would definitely cause a fuse to go and fans on those things are pretty cheaply made.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#7
http://music-electronics-forum.com/t6723/

contains a schmatic.

Disconnect each power supply circuit on the transformer secondary and connect each one in turn until the fuse blows - then trace down that circuit.

If you don't understand the diagram you're wasting your time anyway really - find a mate who does!

My money would be on a new TDA7293 being needed. Check around there for signs of damage.

Like acoustic mirror says there is no output transformer - solid state amps (generally) don't need them.
#9
You connected a solid state amp directly to an interface to record? You likely have blown the output transistors, or IC module. Depending on the cost of the amp, it may not be worth it to have it repaired. I know it's a little late for this now, but never connect the output of any amp into a mic or line input. Nothing good will come from it.
#10
Quote by KG6_Steven
You connected a solid state amp directly to an interface to record? You likely have blown the output transistors, or IC module. Depending on the cost of the amp, it may not be worth it to have it repaired. I know it's a little late for this now, but never connect the output of any amp into a mic or line input. Nothing good will come from it.


using the line out. But ive read you still need a speaker cabinet connnected, which i didnt.

How could i check if the fan is shot/causing a short?
(signature removed, please choose another)
#11
You don't need a cabinet connected. And don't listen to anyone that thinks a solid state amp has an OT. Tube amps have OTs to convert high voltage/low current to low voltage/high current. The reason why you need a cabinet connected to a tube amp is because the high voltage can build up and arc inside the amp if the OT doesn't have a speaker connected. Think of high voltage like pressure building up inside the amp until it pops. SS amps don't have a high internal voltage and are capable of running without a speaker connected.

That link PSimonR posted and the schematic are your best bet if you are comfortable with messing around with electronics.

http://music-electronics-forum.com/attachments/14445d1310140834-marshall-mg100hdfx.pdf
#12
Quote by Enteroctopus
Roll up a piece of aluminum foil. Works for me!


i have a problem with this.

i know you are not serious, but not everybody may. it could likely wreck the amp, start a fiire, etc.

just be a little more careful, some people don't know the ramifications of that.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/
#13
Yeah ive pretty much given up lol. I disconnected the fan, but have no idea how to see if it still works. the amp blows a fuse with it disconnected as well.
(signature removed, please choose another)