Fender SWR LA12 Notes

Bass amplifier

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TECH NOTES

8860 E. Chaparral Road, Suite 100, Scottsdale, Arizona 85250

TECH NOTE # TN 04-2

PRODUCT(S) AFFECTED:

SWR LA12 and LA15 Bass Amplifiers; all voltages.

SYMPTOMS:

Power Amp Bias misadjustment and/or incorrect heatsinking of V

Q2 which can lead to catastrophic failure on the Power Amp PCB assembly.

CONDITION:

Over biasing the Power Amp causes the current at the Output emitter resistors to reach

levels between 625mA to 1.25A. Also, some cases show the V

Q2 is not properly attached to the heatsink. The above two conditions can contribute to

thermal runaway occurring on the Power Amp. This will lead to the catastrophic failure

by either R6 or R9 igniting when the unit is at idle (unit powered ON with no instrument

input). This proceeds to destroying the PCB assembly.

PARTS REQUIRED:

None

Fender Musical Instruments Corp.

ISSUE DATE:

Oct 2004

ISSUED BY:

Mike Ulrich

PAGE:

1 of 7

Multiplier transistor

multiplier transistor

Page 1 Mike Ulrich PAGE: 1 of 7 PRODUCT(S) AFFECTED: SWR LA12 and LA15 Bass Amplifiers; all voltages. SYMPTOMS: Power Amp Bias misadjustment and/or incorrect heatsinking of V Multiplier transistor Q2 which can lead to catastrophic failure on the Power Amp PCB assembly.
Page 2: Warranty Claim Instructions
TECH NOTE # TN 04-2 PAGE: 2 OF 7 REQUIRED ACTION: Take the following corrective actions (reference attached schematic and PCB assembly drawings): 1. Remove chassis from cabinet by removing 10 mounting screws. Lift the chassis out the rear of the cabinet. Disconnect the speaker wiring from cabinet by removing the cable clamp from the inside of the cabinet.

Swr la15