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Old 9th November 2010, 12:40 PM   #1
AJD is offline AJD
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Join Date: Nov 2010
Default AVT 20/ components

Hi All,

I am new to this forum so please excuse if i am posting in the wrong place.

I am also new to electrical components so please excuse if this is a basic question.

I have an old Marshall AVT20 amp, that was broken. It was making a motorboating noise. I have taken the board out and found that there is a blown resistor and capacitor. The resistor is at marking R53 on the board and the capacitor at C71 (this seems to be a common problem, i have noticed while scanning through other forums).

The Capacitor (which is i believe a Metalized Polyester Film capacitor) is marked .22J63
Now my understanding is that that is 63V but what is the ".22"? the schematic shows 220n? what is the n?

The Resistor is so fried i cant see anything on it but the schematic says 1/2W and "10R". Is that 10 Ohm? 100ohms? what is the "R"?

Any help would be much appreciated.

Also, would it be fatal to the amp if you put different resistor values and capacitor values instead?
(this last question i am pretty sure is "yes" but i am not totally sure so i thought it worth asking)


Many Thanks
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Old 9th November 2010, 04:32 PM   #2
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Join Date: Oct 2007
My guess is the .22 means .22micro farads.
The n is for nano, as in 220nF = 220x10^-9 farads.
The R does in fact stand for ohms, so 10R = 10ohms.

Using components with different values would be a bad idea. You shouldn't have any difficulty getting your hands on that value resistor and cap. Also, it would be beneficial to figure out why they fried since replacing them might not do anything but fry the new parts.
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Old 10th November 2010, 04:25 AM   #3
AJD is offline AJD
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Join Date: Nov 2010
Thanks Mahawk,
Much appreciated. I will have a look and see if there could be an underlying problem.

Thanks Again
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Old 11th November 2010, 07:37 AM   #4
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
Those two parts are your zobel stability network, they are there to prevent the amp from going into high frequency oscillation. And of the system goes there anyway, these parts can burn up trying to shunt off the signal. They are in series with each other, and the pair of them is from the power amp output to ground.

Quite possible the TDA2050 power amp IC is faulty, a new one would be worth the few dollars it costs just for peace of mind.


This parts section is a good place to ask what the parts are, the repair of the amp is probably better down in the musical instrument section or at least solid state amps. They may or may not decide to move it.
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