SERVICE BULLETIN NO. 1428

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(OVER) Date: September 29, 2025 (S) (M) SERVICE B ULLETIN NO. 1428 PIPER CONSIDERS COMPLIANCE MANDATORY ATA/JASC: 2430 Piper Aircraft, Inc. 2926 Piper Drive Vero Beach, FL, U.S.A. 32960 SUBJECT: PERIODIC INSPECTION OF DIODE COOLER ASSEMBLY MODELS AFFECTED: SERIAL NUMBERS AFFECTED: PA-28-140 Cherokee 140 28-7525001 thru 28-7725290 PA-28-180 Cherokee 180 28-7105001 thru 28-7205318, 28-7505001 thru 28-7505260 PA-28-151 Cherokee Warrior 28-7515001 thru 28-7715314 PA-28-161 Cherokee Warrior II 28-7716001 thru 28-8616057, 2816001 thru 2816109 PA-28-181 Archer II 28-7690001 thru 28-8690056, 28-8690061, 28-8690062, 2890001 thru 2890205 PA-28-201T Turbo Dakota 28-7921001 thru 28-7921095 PA-28-235 Cherokee 235 28-7510001 thru 28-7710089 PA-28-236 Dakota 28-7911001 thru 28-8611008, 2811001 thru 2811050 PA-28R-200 Arrow II 28R-7535001 thru 28R-7635545 PA-28R-201 Arrow III 28R-7737001 thru 28R-7837317 PA-28R-201T Turbo Arrow III 28R-7703001 thru 28R-7803373 PA-28RT-201 Arrow IV 28R-7918001 thru 28R-8218026 PA-28RT-201T Turbo Arrow IV 28R-7931001 thru 28R-8631004, 2831001 thru 2831038 PA-32-260 Cherokee Six 32-7500001 thru 32-7800008 PA-32-300 Cherokee Six 32-7540001 thru 32-7940290 PA-32-301 Saratoga 32-8006001 thru 32-8606023 PA-32-301T Turbo Saratoga 32-8024001 thru 32-8424002 PA-32-301FT 6X 3232001 thru 3232067 PA-32-301XTC 6XT 3255001 thru 3255051 PA-32R-300 Lance 32R-7680001 thru 32R-7880068 PA-32R-301 Saratoga SP 32R-8013001 thru 32R-8313030, 3213001 thru 3213108 PA-32R-301 Saratoga II HP 3246001 thru 3246237 PA-32R-301T Turbo Saratoga SP 32R-8029001 thru 32R-8329040, 3229001 thru 3229003 PA-32R-301T Saratoga II TC 3257001 thru 3257410 PA-32RT-300 Lance II 32R-7885001 thru 32R-7985106 PA-32RT-300T Turbo Lance II 32R-7887001 thru 32R-7987126 PA-38-112 Tomahawk 38-78A0001 thru 38-78A0800 SERVICE BULLETIN NO. 1428 PAGE 2 of 5 COMPLIANCE TIME: Initial compliance must coincide with the next regularly scheduled maintenance event, but must not exceed the next 50 hours time in service (TIS). Thereafter, recurring compliance must be accomplished during each regularly scheduled maintenance event or each 100 hours TIS, whichever occurs first. APPROVAL: The content of this service document has been reviewed and determined to already comply with applicable Federal Aviation Regulations. PURPOSE: It has been determined that a short circuit can possibly occur between the diode cooler assembly and the attachment hardware caused by wear of the insulating washers (i.e., Delrin insulators) or the diode cooler assembly may have been accidentally struck or contaminated with a ferrous residue during maintenance. This service bulletin mandates the recurring inspection and, on condition, replacement of the insulators and attachment hardware. INSTRUCTIONS: NOTE: The inspections described herein shall be accomplished using a 10X magnifier, a mirror, and a suitable light source or other equipment capable of providing equal or better resolution. 1. Locate and disconnect the battery. 2. Locate and gain access to the diode cooler assembly. NOTE: The location of the diode cooler assembly varies between aircraft models. For PA-28-140/151/161 models, the diode cooler is located under the rear seats floorboard. For PA-28-180/181/235 and PA-28R-200/201/201T models, the diode cooler is typically located on the battery shelf aft of the rear cabin bulkhead closeout. For all other models, refer to the applicable Piper airplane maintenance manual for the location of the diode cooler. 3. Visually inspect the diode cooler assembly, including wiring and insulators, for condition/damage (cracks, wear, deterioration, evidence of overheating, electrical shorts, ferrous or other residue), improper installation including insufficient/excessive insulator screw torque, etc. See Figure 1. • If one or more of the insulators show signs of damage, replace all 4 of the insulating washers, Piper part number (P/N) 467-067, and, on condition, the fastener hardware (screws, washers, nuts, etc. as applicable to the current installation). Take great care to avoid over-torquing during installation to prevent damaging the insulators. See Figure 2 for examples of fastener hardware and stackup. NOTE: There are two typical configurations for fastener hardware securing the diode cooler assembly; Configuration A uses a screw and nut and Configuration B uses a screw and nutplate (i.e. anchor nut). Certain configurations will also use a washer under the screw head. The exact hardware will vary between each aircraft model Take note of what fastener hardware in the existing installation before discarding and replacing any fastener hardware. • If evidence of overheating or electrical shorts is discovered, inspect the electrical power distribution system for condition/damage (including wiring) and replace components as required. Refer to the applicable Piper illustrated parts catalog (IPC) for P/Ns. • If ferrous or other residue is discovered, clean the diode cooler assembly and the surfaces local to the assembly when installed in the aircraft. If required, remove the assembly from the aircraft to clean. WARNING: ENSURE THE FASTENER HARDWARE, IN PARTICULAR THE WASHER (IF INSTALLED), DOES NOT INTERFERE WITH THE ELECTRICAL ISOLATION OF THE DIODE COOLER. IMPROPER INSULATION RISKS THE POSSIBILITY OF AN ELECTRICAL SHORT BETWEEN THE DIODE COOLER AND THE AIRFRAME, RESULTING IN FAILURE OF THE ELECTRICAL SYSTEM AND/OR FIRE. 4. Reconnect the battery and perform a functional check of the aircraft's electrical system by alternator functionality, including alternator inoperative warning annunciation, must be verified in accordance with the applicable Alternator and Annunciator System Test Procedures in the aircraft Maintenance Manual. 5. Make a logbook entry documenting compliance with this service bulletin. Include a description of any conditions that were discovered during the inspection and servicing that was performed.