More Marshall Valvestate Problems

poison · 21st January 2011, 12:51 AM

Ok here is another one...

No visible signs of any fryups or blow outs but when i plug it in it blows the fuse (2a 250v) straight away...

Any ideas?

llwhtt · 21st January 2011, 01:51 AM

If it uses the typical output IC (TDA7293?), try unplugging the output module and a new fuse. If it doesn't blow probably bad IC. Of the many that I have worked on that's usually the only thing wrong but sometimes the IC wipes out some parts on the main board also.

Craig

madtecchy · 21st January 2011, 07:16 AM

I have seen a few of these as craig says it is more than likley the output ic.
also check the mute circuit as i have found that when the ic self destructs it takes out a resistor in the mute circuit..
Mad Mark

llwhtt · 21st January 2011, 03:06 PM

Those are the parts on the main board I was thinking of, check the zener diode in the mute circuit. The last amp I repaired it was shorted. If it ends up being the output IC you will have two choices, replacing just the IC or replacing the whole module.

Craig

poison · 21st January 2011, 03:46 PM

Hmmmmmmmmmm....

This is doing my head in... am i looking for an obvious burnout? or is it a case of replacing and testing?

All solders and connections on the IC's are fine... ill check the zener diode on the mute circuit when i am back in the studio later tonight but as i said... no obvious burnouts or bad connections...
Poison Pete

llwhtt · 21st January 2011, 05:03 PM

There may not be anything visible, sometimes they go with flames and sometimes they don't. Unplug the module and power it up.

Craig

madtecchy · 22nd January 2011, 10:25 AM

Quote:

Originally Posted by poison

Hmmmmmmmmmm....

This is doing my head in... am i looking for an obvious burnout? or is it a case of replacing and testing?

All solders and connections on the IC's are fine... ill check the zener diode on the mute circuit when i am back in the studio later tonight but as i said... no obvious burnouts or bad connections...
Poison Pete

Even if you did find a burnout there would still be a very good chance other components will have be damaged with no visible sign. Through past experience it will deff be the tda output ic. you may find that when removing the ic a leg will fall off because of damage. order yourself a new tda and fix your amp. Regards Mad Mark

poison · 22nd January 2011, 11:12 AM

Cool... Ive got it.

TDA it was...

Thanx so much guys!

Poison Pete

21st January 2011, 12:51 AM	#1
poison diyAudio Member Join Date: Jan 2011 Location: London	More Marshall Valvestate Problems Ok here is another one... No visible signs of any fryups or blow outs but when i plug it in it blows the fuse (2a 250v) straight away... Any ideas?

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21st January 2011, 01:51 AM	#2
llwhtt diyAudio Member Join Date: Jun 2008	If it uses the typical output IC (TDA7293?), try unplugging the output module and a new fuse. If it doesn't blow probably bad IC. Of the many that I have worked on that's usually the only thing wrong but sometimes the IC wipes out some parts on the main board also. Craig

21st January 2011, 07:16 AM	#3
madtecchy diyAudio Member Join Date: Dec 2010 Location: wigan	I have seen a few of these as craig says it is more than likley the output ic. also check the mute circuit as i have found that when the ic self destructs it takes out a resistor in the mute circuit.. Mad Mark

21st January 2011, 03:06 PM	#4
llwhtt diyAudio Member Join Date: Jun 2008	Those are the parts on the main board I was thinking of, check the zener diode in the mute circuit. The last amp I repaired it was shorted. If it ends up being the output IC you will have two choices, replacing just the IC or replacing the whole module. Craig

21st January 2011, 03:46 PM	#5
poison diyAudio Member Join Date: Jan 2011 Location: London	Hmmmmmmmmmm.... This is doing my head in... am i looking for an obvious burnout? or is it a case of replacing and testing? All solders and connections on the IC's are fine... ill check the zener diode on the mute circuit when i am back in the studio later tonight but as i said... no obvious burnouts or bad connections... Poison Pete

21st January 2011, 05:03 PM	#6
llwhtt diyAudio Member Join Date: Jun 2008	There may not be anything visible, sometimes they go with flames and sometimes they don't. Unplug the module and power it up. Craig

22nd January 2011, 11:12 AM	#8
poison diyAudio Member Join Date: Jan 2011 Location: London	Cool... Ive got it. TDA it was... Thanx so much guys! Poison Pete

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