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How To Update A20 From MKII To MKIII

Make sure the amplifier is not connected to the mains.
Take the top-cover off the amplifier.
Locate and change the following components:

R5, R105 to 280R

R1, R101 to 380R

R2, R4 to 7,5K

R36, R136 to 620R

C19, C119 to 470pF

The seize is either 0805 or 1206 depending on the age of the amplifier.
The pictures is applying on 0805. On the 1206 variant they are located a bit different,
check Service Manual.

After this is done, power up the amplifier and check that it works.
Power it off and remove the two Shortlinks on the board, power it up again and let it be warm.
(Just let it run without any signal for half an hour).
Measure the bias on the pins where the shortlinks where located, you should adjust it
With the potentiometer to 13mVon each channel.
Recheck after another half an hour.
Power it off and refit the shortlinks.
Refit the cover.

Now you are done!
Overwiev of the A20

Bias Trimmer Shortlink Left Shortlink Right Bias Trimmer
Left Channel Channel Channel Right
Close Look Right Channel
Temporarily remove the heatsink on REG2

R136

C119

R4
R101
Close look Left Channel

R105

R5

C19
R1

//Björn Holmqvist
Primare Systems AB