Fender Twin Amp 1994 Service Manual page 16

TECH NOTE # TN96 - 3
PRODUCT(S) AFFECTED:
'94 TWIN AMP
(All Serial numbers prior to LO-673648 should require this modification)
SYMPTOMS:
Overheating of power tubes when in the LOW OUTPUT power mode.
Unit appears to be locked into the HIGH OUTPUT power mode.
CONDITION:
Arcing between switch contacts in the high voltage leg of the HIGH/LOW OUTPUT
power switch (S9). The arcing occurs only when the HIGH/LOW OUTPUT switch is
operated while the amplifier is in the fully on mode (NOT IN STANDBY). This may
cause burning, pitting, and eventual welding together of the switch contacts. Therefore
when the amplifier is switched to the LOW power mode, the high voltages at the output
tubes remain high, but the Bias voltage drops. The result is a severely under Biased
output stage that quickly overheats.
REQUIRED ACTION:
A new style switch has been specified for this application.
Determine if the old style switch is installed in the unit. The old style switch is identical
to the Power and Standby switches. If the old style is present, order P/N 049976
SWITCH TOGGLE DPST DC W/NUT. The new style switch will have a pair of White &
Black leads as opposed to Faston lugs. The leads must be soldered directly to the
power supply PCB. This is to comply with safety regulatory agencies (U.L.,C.S.A.).
DO NOT SPLICE THE SWITCH LEADS WITH THE EXISTING JUMPER WIRES.
TECH NOTES
Fender Musical Instruments Corp.
7975 North Hayden Road Scottsdale, Arizona 85258
ISSUE DATE: March, 1996
ISSUED BY: C. Colaço
PAGE: 1 of 2