My Kenmore 80 series dryer runs nice and hot but will not stop... is it the timer or thermostat? How do I know?

There are many questions about the kenmore dryer. I even had one 2 moths ago and no one is answering them. Try this... Epinions.com - Posts in Sears Kenmore Elite Dryer Won't Run If Start Button Released (http://www.epinions.com/msg/show_~threads/cat_id_~17/id_~2440/forum_id_~409/sec_~forums/pp_~8)

It does seem that Sears Kenmore washer and dryers have more than their fair share of repair questions. Thermostat regulates the temp but the timer stops the dryer. I'd strongly suspect the timer. The top housing should open after you remove the end caps. Take a look at the backside of the tower.

We have had some good people in appliances, but they disappeared. The thermostat turns the heat on and off. When the timer times out, contacts should open breaking the circuit to the coil of a relay. Then contacts in relay should open stopping the motor and shutting off the heat. If it stops when you open the door, it is the timer. If it keeps going with the door open, it is the relay.

I FOUND THIS ALSO...
Ok Summary time..
** KENMORE / SEARS DRYERS AFFECTED **
110.63932100
110.63932101
110.63932102
110.63942101
110.63942102 (?)
110.63952101
110.63952102

** 2 problems are being discussed **
1-Push start button, release, dryer stops
a.)Heater Relay (Part 3405281 ) has burned out.
b.)The "Computer" or Circuit board has died and will
No longer power the relay(s).
(The start button bypasses the relay, which is why
It works until you let go.)

2-Dryer runs normally, but no heat.
a.)The circuit board has fried. Usually obvious burns
On board to resister R2 (4.7kohms)

Sears is aware of the problem, and has issued an internal Service Bulletin, or Service Flash # SF26-751. Some people have gained some financial relief IF the problem is from the circuit board kind of failure. However the Relay itself does not appear to be covered. And the Service call itself to determine if the part is covered is also not covered.

** The 2 Boards or "Computers" affected
( Not to be confused with the PCB # 3976633 )
3978949
3978954

The upgraded "Replacement" board for some appears to be # 8546229. Based on the photo, it appears they replaced the 5 Zener Diode array with a single larger Zener. (A Zener and a Resistor create a cheap voltage regulator circuit.)

Numerous calls have been made to get some kind of class action lawsuit or consumer advocacy group involved, but a search today shows no takers. (I did find out our Calypso Washer was though.. ) Sears Management is aware of the problem and has only acted in a couple of cases, while others have been refused.

** For do it yourselfers **

Remove the side covers on the control panel. Remove the 2 screws. On the rear, detach the cover at the white plastic clips. There is a schematic inside. There are 2 identical relays. One for motor, one for heat element.

I purchased a relay on eBay for about $15. FSP appliance part # 3405281 or Potter & Brumfield p/n T9AP1D52-48-03

The circuit boards are available from Sears Parts for $79 (3978954) or $119 (8546229) plus ship. 8546229 also on eBay for about $70.

Some success has been achieved by replacing damaged components, but I found Radio Shack does not carry them, and I could not find an Internet Retailer that has a minimum order low enough to make this feasible.

Quoting Roy:
Zener diodes, D2-D6 were shorted. Replaced ( 1N4738A 8.2v zener)
D7 was open. Replaced (1N4738A 8.2v zener)
C2 swollen and leaking. Replaced 220/63v
C25 swollen and leaking replaced 333/63v
R2 burnt open. Replaced 4.7k 1/2 watt
Q2 shorted. MPSA56 replaced with NTE159

I FOUND THIS ALSO...

Diagnostic Guide Link
I found service tech diagnostic guides (PDF format) during an online search. This includes instructions on putting the dryer into test mode in order to check switches, etc. Here are the links:

Gas Dryer:
http://www.servicematters.com/docs/wiring/Tech%20Sheet%20-%203980053.pdf

Electric Dryer:
http://www.servicematters.com/docs/wiring/Tech%20Sheet%20-%203979705.pdf

The tech sheets are a goldmine in information!