Used TriAxis, no gain, muddy

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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Herfstbokkie
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Joined: Fri Aug 21, 2020 5:39 am

Used TriAxis, no gain, muddy

Post by Herfstbokkie » Fri Aug 21, 2020 5:47 am

Hello all, great to be here with Mesa enthusiasts.

Since a couple of days I got a TriAxis, a V1, serial number T0861 (so no recto board). The screen says 2.0 when firing it up.

LD1 and LD2 don't have the amount of drive it should have; when playing with the following settings on LD1 Red (Gain 7.0, treble 7.0, middle 3.5, bass 0 and LD1 drive 6) it's almost a clean sound. When pushing the drive up it sounds more like a fuzz pedal. The same with LD2, although that sounds very muddy as well, completely unusable.

What I have noticed as well is that when LD2 is engaged, the Lead 1 drive seems to have effect on that channel, even though that should be impossible. My first thought was that maybe the tubes were bad, so these were replaced by JJ's, without any effect. I suspect some capacitors or LDR's.
One particular weird thing is that when the Lead modes are engaged, and I hit a string and turn off the amp I hear a massive nice distorted tone, the way it should sound, but only when it is powering off. Tube circuit issue?

Anyone here who experienced similar problems and know where to start looking?
I already like some of the tones and character this thing produces so I can't wait to restore it to former glory. Thanks in advance.

Edit; when testing, C122 seems to have effect on the amount of drive. When measuring the voltage across the capacitor the drive increases massively for both red channels.

Synrgy77
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Posts: 17
Joined: Wed Dec 11, 2019 7:40 pm

Re: Used TriAxis, no gain, muddy

Post by Synrgy77 » Tue Oct 06, 2020 10:07 am

Look for bad tantalum (yellow) capacitors and 75492 circuit (IC on the left). They are part of the switching system.

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