Kenmore (LG) Dryer 796.81372210 - stopping with damp clothes/towels, is it PCB or just life?

[original_sound]

Our Kenmore dryer has been stopping early on auto cycles with clothes, and especially towels, still damp or wet.  It did not do this for the first ~10 years or so of its life.  I suspect that an electrolytic capacitor in the moisture sensor circuit on the PCB has failed or is out of tolerance (see Patent #US8707580B2 for description of typical moisture sensor circuits). Unfortunately, the PCB board and components are embedded in epoxy, so rather than recapping the board for a few bucks to see if that fixes it, I am going to have to replace PCB if that is the problem, and I think it is.  Troubleshooting and tests run so far:

• Dryer dries fine aside from moisture sensing - good air flow (clean duct, no restrictions) and temperature
• Tried cleaning the moisture sensor bars
• Replaced the moisture sensor bars
• Moisture sensor mechanical tests passed - continuity from NA6 to chassis ground screw, continuity between sensor bars with NA6 OR and BL jumpered
• Range of moisture sensor readings when running functional diagnostic is 37 (soaking wet cloth) to 253 (open) versus spec of 30 to 239

The readings from the functional diagnostic suggest to me that the circuit is out of calibration (perhaps bad capacitor as hypothesized), but wondering if collective wisdom here agrees that the deviation is enough to cause the symptoms before I spring for a new PCB.  Only other option is to just replace dryer as the chief laundry officer has had enough of the damp towels.

 

[Vance R]

On 11/2/2022 at 5:47 AM, original_sound said:

Moisture sensor mechanical tests passed - continuity from NA6 to chassis ground screw, continuity between sensor bars with NA6 OR and BL jumpered

Seems you have followed the flow chart correctly leaving you with the main board as the culprit. The moisture strips are in the front part of the dryer, check to see that the dryer is level or slightly tilted to the front so the clothes are rubbing on the bars.

[original_sound]

I hadn't thought about the leveling.  That's a good point.  Should be ok but will check that before buying a new board.

[original_sound]

I ended up replacing the PCB with a salvage unit and the dryer seems to be performing properly now - first two loads of towels finished dry and I actually saw the timer go up instead of constantly down, which suggests some successful moisture sensing.  To my surprise, the moisture test readings with the new PCB were similar to those of the old one - the range was 52-253, which would suggest a dry bias compared to both spec and the old PCB.  It did seem like the display values changed much more quickly with the new PCB (ie, it seemed more responsive), so maybe that reflects the repair.