Mesa/Boogie TriAxis Refurbishment

TriAxis Serial Number: T0111

Modifications: Version 2 with Phat Mod

Problem 1:

When I received the unit it needed new tubes. After installing the new tubes the unit sounded like it had lost all power. The output was much too low and it sounded like there was a wet blanket in front of the speaker cabinet.

Fix 1:

Inspected wires connected to the TX4 board. One of the wires (red, closest to power input) had become disconnected. Reconnected the wire. DONE

Problem 2: After playing for some time the unit will become “confused” and switch patches at random, the lights on the display including the 7-segment displays will flicker at random. When the unit comes back to its senses the patch I’ve programmed are lost.

Fix 2:

Replace optoisolator. Sources on the internet identify the optoisolator associated with the MIDI circuitry to be the culprit.

The wrong part was installed (6N139) which caused erratic MIDI patch change behavior and in some cases no response from MIDI input. Installing the correct part (6N138) resolved the issue. DONE

Problem 3:

Unit is over 20 years old and requires preventive maintenance.

Fix 3:

Replace all electrolytic capacitors. Inspect all point-to-point wiring. NOT DONE

Capacitor List:

BoardPositionTerminationCapacitanceVoltage
TX2CNear FL11Axial3300uf10
TX2CC3Axial4700uf25
TX2CC4Radial1000uf25
TX2CNEAR CR2032 BATTERYRadial100uf6.3
TX2CC33Radial100uf6.3
TX3AC1Radial100uf6.3
Rear PCBNear Q5Radial1000uf25
Rear PCBNear Q5Radial1000uf25
Rear PCBNear Q5Radial1000uf25
Rear PCBNear Q5Radial1000uf25
Rear PCBNear DVAxial3300uf10
Rear PCBNear MainsAxial30uf500
Rear PCBNear MainsAxial30uf500
Rear PCBNear MainsAxial30uf500
Rear PCBNear MainsAxial30uf500
Rear PCBTo Upper Right of IC3Radial1uf50

Digikey BOM:

Manufacturer Part NumberManufacturerDigi-Key Part NumberQuantityUnit PriceExtended PriceDescription
6N138Lite-On Inc.160-1795-ND50.81$4.05OPTOISO 5KV DARL W/BASE 8DIP
SN74LS14NTexas Instruments296-1643-5-ND50.67$3.35IC INVERTER SCHMITT 6CH 14DIP
UKA0J101MDD1TDNichicon493-4618-1-ND30.41$1.23CAP ALUM 100UF 20% 6.3V RADIAL
UKA1E102MPDNichicon493-15328-ND51.08$5.40CAP ALUM 1000UF 20% 25V RADIAL
MAL202116472E3Vishay BC Components4328PHBK-ND14.17$4.17CAP ALUM 4700UF 20% 25V AXIAL
MAL202114332E3Vishay BC Components4012PHBK-ND22.77$5.54CAP ALUM 3300UF 20% 10V AXIAL
UDB1H010MPM1TDNichicon493-13355-1-ND10.62$0.62CAP ALUM 1UF 20% 50V RADIAL

Parts harder to obtain:

OPA2604AP low noise OP AMP replacement must be sourced from Chinese vendors on eBay.

VTL5C9 Audio Opto-Coupler only manufactured by Xvive in China.

There is a US based retailer for VTL5C9

http://smallbear-electronics.mybigcommerce.com/photocoupler-vactec-vtl5c9/

Mains filter capacitors:

https://www.tubesandmore.com/products/capacitor-sprague-atom-aluminum-electrolytic