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Home›Repair guides›Generac›Procedure for Checking Control Board Number 76009A

Generac — Procedure for Checking Control Board Number 76009A

Testing & diagnosis · Liquid Cooled GUARDIAN PCB 76009A

From a Generac service manual covering: 4077, 4079, 4109, 4389, 4390, 4456, 4674, 4675. Check it applies to your exact model before use.

Applies to: Generac 4077, Generac 4079, Generac 4109, Generac 4389, Generac 4456

Before you start

  • Record your measurements and include these findings on the Warranty Repair Report or the claim will be rejected.
  • Be careful when pushing the SW1 switch, there is LIVE voltage present on the PCB.

Procedure

  1. With Auto/Off/Manual in Auto or Manual, check for battery voltage from wire #15A (J1-10) to wire #0 (J1-13); should be 12-14 VDC.
  2. IF STARTER DOES NOT CRANK: measure #56 wire (J1-5) to #0 (J1-13) within 5 seconds of placing unit to manual; should be greater than 10 VDC.
  3. If less than 10 VDC, remove #56 wire from J1 housing and re-measure across J1-5 to J1-13; if still less than 10 VDC, replace the board.
  4. Also check for a short to ground on wire #56 which could damage the board.
  5. IF STARTER CRANKS BUT UNIT DOES NOT COME UP TO SPEED: measure #14 wire (J1-7) to ground (J1-13) while cranking; should be greater than 10 VDC.
  6. If less than 10 VDC, remove #14 wire and re-measure J1-7 to J1-13; if still less than 10 VDC, replace the board.
  7. IN AUTO - UNIT DOES NOT TRANSFER AFTER UTILITY LOSS & 20 SECOND WARM-UP DELAY: measure #23 (J1-3) and #194 (J1-4); should be greater than 10 VDC.
  8. If not, remove #23 and #194 wires and re-measure J1-3 to J1-4; if less than 10 VDC, replace the board; also check for a short to ground on #194.
  9. IN AUTO - UNIT DOES NOT TRANSFER BACK TO UTILITY WHEN UTILITY VOLTAGE IS RESTORED: check voltage between J1-14 (red wire) and J1-15 (#225A wire); should be greater than 12 VAC.
  10. If utility is near rated (208 VAC or 240 VAC) and secondary is less than 12 VAC, check transformer wiring; if greater than 12 VAC and still no return, replace the board.

Specs & values

Full service-parts list: Generac 4077 →, Generac 4079 →, Generac 4109 →, Generac 4389 →, Generac 4456 →

Source: Generac service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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