Fender Twin Amp 1994 Service Manual - Description of Changes

’94 TWIN AMP

ADDENDUM

DESCRIPTION OF CHANGES

All of the following modifications are present on revision “E” printed circuit boards.  Some of the

other modifications appear on earlier revision PCBs.

The PCB revision level is located on the solder side of the centermost PCB, near the orange wire

and filter capacitor C40.

Reason For Changes:

Compliance with Safety Regulatory Agencies:

Added “Crowbar” protection circuit (CR33 – 38) to the screen (Z) supply

capacitors (C40, 41).  The crowbar circuit is present on Revision D & E

printed circuit boards.

Do not attempt the above modification to earlier revision PCBs.

Added RF emissions suppression capacitor (C64, P/N 025995) across the high

voltage transformer secondary, prior to the full-wave bridge rectifier circuit.

Performance modifications:

Added CR32 and changed R124 and R134 to ensure that Relays K1, K2, and K3 

drop out when de-energized.  (See zone 7B on Rev C schematic).

Refer to Tech Note TN95-4

Upgraded the HIGH/LOW OUTPUT power switch.

Refer to Tech Note TN96-3

Changed the Reverb muting circuit to eliminate noise in the reverb recovery circuit 

caused by poor power line conditions.  Change R59 from 100k to 1.8k, add Q2 

(JFET) and R155 (1.8k).  (See zone 4C on rev C schematic).

Refer to Tech Note TN96-5

Attached is a Revision C schematic/service diagram.