Question about Marshall MG100HDFX 100-Watt Amplifier Head

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Cooling fan ,heat sink MG100HDFX does fan blow out or **** cool air in? Someone left it unassembled..

Basket case head. fan install in or out?

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If you can get two IN then do it but make sure one is pushing air out and the other sucking in.

Posted on Sep 09, 2009


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Popped lights on no sound

Probably smoked the output IC(it is the chip mounted to the heat sink attached to the fan) which can be purchased from marshall directly or from one of their service centers. Also P-H216 sold at should work. No soldering required. Look at that IC(chip) to see if it looks burnt or has a crater on it which would indicate that that is indeed you bad component.

Mar 18, 2014 | Marshall MG100HDFX 100-Watt Amplifier Head

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I got a Marshall MG100HDFX for free from a friend stating it was blown. I asked how this happened and he said that one of his friends plugged in another speaker or amp into the second speaker input in the...

The power amp section has blown parts. You will likely find they use a chip like the TDA7293 as the power amp output and it will be blown, shorted causing the fuse to blow. These cost $6 from Find a competent tech to replace it and use heat sink compound. Verify the part before ordering one. They come with leads bent either way so make sure you get the one with a matching suffix letter. When firing up after repair, put a 60 watt light bulb in series with the hot power lead to act as a current limiter... saves blowing fuses if there is another problem.

Jun 21, 2011 | Marshall MG100HDFX 100-Watt Amplifier Head

1 Answer

I have the Marshall MG100HDFX 100-Watt Amplifier Head, the fuse was blown and there is no audio coming out of the the spkr jacks. this is how i received the amp and have no further info to diagnose. im...

If the output transistors have shorted, it is LIKELY that several others in the drivers and even farther back have also gone. HOWEVER some Marshall amps use one or more TDA7293 chips. These require installation using heat sink compound. The TDA7293 can be found at:

They come in two sexes depending on which way the leads are bent for installation. You have to see how yours are mounted relative to the circuit board. Cost about $6.

Apr 24, 2011 | Marshall MG100HDFX 100-Watt Amplifier Head

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GM100HDFX head. Fuse blows immediately upon power up when output module on fan-cooled heat sink is plugged in. Increase the fuse and loud buzz comes out through the speaker. No volume control then. Unplug...

NEVER increase or replace the fuse without repairing the unit. Further damage is likely if you do so.

Put a light bulb, say 150 watts in series with the power to the unit to act as a fuse that won't damage things while troubleshooting. The light will light and limit the current.

There are three 47mfd/63V electrolytics on the output module. I suspect one of those is shorted. Observe the correct polarity when replacing. C2 and C3 are most likely. Use my above suggestion with the light bulb and check the voltage across each of these. It should likely be in the 35 to 45 volt range though schematic doesn't show the value..

Aug 04, 2010 | Marshall MG100HDFX 100-Watt Amplifier Head

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Hardest thing is getting the chassis out past the Tolex covering. Sometimes it catches and you have to use a knife blade to hold it out of the way.

Make sure to use an identical fan with identical ratings. Some of these are throttled depending on sensed heat. For those, an exact model fan should be used.

May 09, 2010 | Marshall MG100HDFX 100-Watt Amplifier Head

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My marshall mghdfx head fan makes noise when you first turn it on. what is this?

Some cooling fans are "throttled" depending on the sensed temp... these CAN be noisy upon initial startup.

It can also be bearings going out... best plan is to watch it and see if it gets worse.

Changing a fan is fairly easy. You have to observe the polarity of the connections. Replace with identical unit.

May 09, 2010 | Marshall MG100HDFX 100-Watt Amplifier Head

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Dear experts, i have a MG100HDFX and no sound seems to come out. i replaced the burnt fuse inside the head and i disconnected the timer for the cooling fan cuz thats what kept blowing the fuse. With the...

The problem is not likely to be the fan. I would suspect the output section of the amp to have a problem. These units use a 15 leg power IC for the output. Look for a small IC attached to the heatsink. It will be marked TDA7293V. This is the likely defective part.


Jan 07, 2010 | Marshall MG100HDFX 100-Watt Amplifier Head

1 Answer

Blows main fuse. Found burnt place on circuit board where connection 1 is. It's the board that's mounted to the heat sink with fan at the back. Disconnected connector 3 that goes to con 1. Now fuse does...

Chances are a power transistor has shorted. Sometimes input rectifier diodes short or electrolytic caps.

Here is a hint to troubleshoot this: Connect a 150 watt lamp in series with the hot side of the power line to the amp. This will limit the current (and voltage) and prevent the fuse from blowing. You can do a lot of troubleshooting at the much reduced voltage.

If board is burnt to carbon, this "cancer" needs to be cut out and removed as the blackened board is slightly conducive instead of an insulator. Often a circuit trace has fried the board. One must install jumpers around ones that have smoked.

Sep 24, 2009 | Marshall MG100HDFX 100-Watt Amplifier Head

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Marshall mg 100hdfx fan

Some of the Marshall equipment uses computer size fans and even on occasion the same connection.

Take the bad fan with you to a computer repair shop it will be much cheaper than a marshall part they should be able to help you out

Sep 09, 2009 | Marshall MG100HDFX 100-Watt Amplifier Head

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