Kohler — Photo Transistor Board Test
Testing & diagnosis
From a Kohler service manual covering: CSG-649, Cummins 4B, Cummins 6B, Ford CSG-649, Ford LSG-423, Ford LSG-875, LSG-423, lsg-875. Check it applies to your exact model before use.
Applies to: Ford CSG-649, Cummins/Onan LSG-423, Cummins/Onan lsg-875
Before you start
- Make sure leads C and E are connected to the correct terminals. Reversal or grounding of C (red) lead will turn the FR Activator full on, resulting in ceiling output voltage.
Procedure
- Disconnect battery, negative lead first.
- Disconnect leads E and C from FR Activator.
- Connect red and black photo transistor leads to ohmmeter (+) and (-); cover the phototransistor; meter should read 300K ohms or higher.
- Shine a bright flashlight on photo transistor board; meter should read 5K ohms or lower.
- If ohmmeter does not respond, reverse ohmmeter leads and repeat check.
- If ohmmeter still does not respond, replace phototransistor board and harness assembly.
- Reconnect C (red) and E (black) leads to C and E terminals of FR Activator.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 300K ohms or higher (covered)
- 5K ohms or lower (lit)
Full service-parts list: Ford CSG-649 →, Cummins/Onan lsg-875 →
Source: Kohler 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.