I have an older, but clean GSH25JFXB defroster that runs for too long, or what I thought, too hot - but let me explain:

The problems started 2 years ago when my defrost elements kept burning out.
I purchased the cheaper ones first and they burned out in 3 months.
Then I purchased an OEM defrost element and that burned out in 8 months.
But always after replacing the element, the defrost period was running normally and I had no steamy issues.

4 weeks ago, it blew again. I replaced it again with a cheaper defrost heater and this is where the problems started.

The heater ran for about 20 minutes and the top of the freezer and ice box melted causing water to drip down into the water dispenser. During the cycle, I observe that the defrost element shuts off around the 15-20 minute mark (no glow) and the freezer then sits quietly for another 5 or 10 minutes warm. Then the freezer compressor kicks in, and after about another 5-10 minutes, the evap fan kicks on.

Now, I have gone down a few rabbit holes. I have replaced the controller board twice. I purchased the first one from eBay, and when that didn't work, I purchased a new one from GE.

I also changed both temperature thermistors and the thermostat that is supposed to cut off when it gets too hot. I've measured the voltages on the J1 connector of pin 3 and pin 4 and they are within tolerance and all components fall within tolerance. I more recently replaced the defrost element. I measured ohms across the element between the new one and the old one and there was a slight difference of 3 ohms. The new one was 22ohms and the old cheaper one was 19ohms. And guess what, it still gets too hot and melts the ice.

I'm at a loss and aa about to give up on this, but thought I would try one more reach out to see if someone with more experience than my DIY electrical skills to offer advice. The unit is otherwise in excellent condition and I think buying a new one didn't make sense at the time, but now I almost wish I did. But perhaps there is something else I missed.

Any advice is welcome.

Awesome - I will run another range test on those thermistors and get back to you. Is it possible though that even with the change of board for a new one from GE, it could exhibit the same problem?