MG100HDFX, No sound after replacing 7293

The Edge · 11-17-2008, 01:39 PM

Hi

A friend asked me to have a look at his MG100HDFXamplifier that was blowing the fuse when beeing turned on.
I found the TDA7293 fried, and have replaced it.
It now powers up fine, and it works perfectly with the headphone output.
I see no other damaged components.
The fan was not running proparly, this might have been the cause of 7293 meltdown, so I oiled the bearings of the fan, and it now runs smoothly.

I do not have a marshall speakercabinet to test with, so hocked up some other speakers just for test, and thought I should at least get some sound out of it, but nothing.. So, what could be wrong?
I guess I should get some sound out of the speaker output even without a marshall cabinet..? Or does the amp for some reason only accept the marshall cabinet?

Is it the preamp that runs the headphones output since this is working, or is this one also driven by the 7293??

I did not have the schematics available when replacing the 7293, so I have not done any signaltracing or anything, but I now found the schematics for the MG100DFX Is this different from the MG100HDFX? In case it is, does anyone have schematics for MG100HDFX?

Thanks in advance

The Edge

JohnH · 11-17-2008, 02:43 PM

I reckon the DFX and HDFX will have the same schematic, so if you can link to it, we can figure out if the headphone is driven by the main output. It would be good if it is, since it means the chip would be working.

John

The Edge · 11-17-2008, 03:11 PM

Quote:

Originally Posted by JohnH

I reckon the DFX and HDFX will have the same schematic, so if you can link to it, we can figure out if the headphone is driven by the main output. It would be good if it is, since it means the chip would be working.

John

Hi

The schematic I found here: ampix - Information

To me it seems like the headphone output may be driven by the preamp, but it is a long time since I read schematics like this, hehe..

But if everything was working ok, shouldn't there be sound on the speaker output with just about any speaker connected, and not only with a Marshall rack?

When I first looked at the pcb board with the 7293, it seems like the chip has been replaced before, so it is possible some of the printleads has burnt of before I soldered on it, But I think I got them all connected..

If the chip is broken again, it is not a big problem since I've got 4 more chips..

JohnH · 11-18-2008, 02:55 PM

the schematic:
http://www.ampix.org/albums/userpics...l_MG100DFX.pdf
Does seem to confirm tha he headphone has its own independent output.

John

11-17-2008, 01:39 PM	#1 (permalink)
The Edge Junior Member Join Date: Nov 2008 Posts: 2	MG100HDFX, No sound after replacing 7293 Hi A friend asked me to have a look at his MG100HDFXamplifier that was blowing the fuse when beeing turned on. I found the TDA7293 fried, and have replaced it. It now powers up fine, and it works perfectly with the headphone output. I see no other damaged components. The fan was not running proparly, this might have been the cause of 7293 meltdown, so I oiled the bearings of the fan, and it now runs smoothly. I do not have a marshall speakercabinet to test with, so hocked up some other speakers just for test, and thought I should at least get some sound out of it, but nothing.. So, what could be wrong? I guess I should get some sound out of the speaker output even without a marshall cabinet..? Or does the amp for some reason only accept the marshall cabinet? Is it the preamp that runs the headphones output since this is working, or is this one also driven by the 7293?? I did not have the schematics available when replacing the 7293, so I have not done any signaltracing or anything, but I now found the schematics for the MG100DFX Is this different from the MG100HDFX? In case it is, does anyone have schematics for MG100HDFX? Thanks in advance The Edge

11-17-2008, 02:43 PM	#2 (permalink)
JohnH Senior Member Join Date: May 2008 Location: Wollongong NSW Posts: 640	Re: MG100HDFX, No sound after replacing 7293 I reckon the DFX and HDFX will have the same schematic, so if you can link to it, we can figure out if the headphone is driven by the main output. It would be good if it is, since it means the chip would be working. John __________________ DSL401 8412 cab Crate Powerblock 1 x 12 Vintage 30 cab '76 Shergold Masquerader '93 Les Paul Studio '83 Roadstar

11-18-2008, 02:55 PM	#4 (permalink)
JohnH Senior Member Join Date: May 2008 Location: Wollongong NSW Posts: 640	Re: MG100HDFX, No sound after replacing 7293 the schematic: http://www.ampix.org/albums/userpics...l_MG100DFX.pdf Does seem to confirm tha he headphone has its own independent output. John __________________ DSL401 8412 cab Crate Powerblock 1 x 12 Vintage 30 cab '76 Shergold Masquerader '93 Les Paul Studio '83 Roadstar

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