Does my Samsung DV350AGP Dryer have a bad motherboard? Tested everything else i could think of!

[getmp3s]

Dear Forum

I've been at this for days trying to rule every other component out to make certain I order the right part to fix my Samsung DV350AGP/XAA Gas Dryer.

The cycle runs, motor spins, controls and display respond normally.  There is no heat.  The igniter does not glow.  There is no AC voltage on the igniter line when the dryer is spinning.  I have first isolated and then conducted resistance tests on all the sensors as follows:

• Igniter resistance is 119Ω
• Thermostat located near the blower is 0Ω
• Hi-Limit Thermostat located on gas chamber reads 0Ω
• Radiant (flame) sensor reads 0Ω
• Thermistor reads 12Ω @ 67°F on the sensor and up at the motherboard as well. 
• Tested the gas valves as well and all are according to manufacture spec at 1.39Ω / 1.28Ω / 0.57Ω
• Tested my belt cut-off switch, door switch and even the lamp are all right on spec. 

So now my attention is turned to the motherboard, there is little information out there on how to test the motherboard but I've tried to test the heater relay switch RY6, it does not change in resistance at any time during a drying cycle or when the dryer is powered off.  Is this normal?  when my meter is at VAC, i do pickup the following on the Heater Relay Switch:

• 0.092AC Voltage when dryer powered ON but not in a cycle
• 0.192AC Voltage when dryer is in a cycle (spinning)
• 0.187AC Voltage when dryer is powered OFF

its so minor i fail to see its significance though unless the heat relay is using this small amount of voltage to trigger another relay somewhere else I have yet to find.  Should the heater relay close circuit when the dryer is running and its failure to do so means the on board relay is bad?  Have i tested it properly?  i just pulled the RY6 header off and Ohms tested pin 1 to pin 2 and go nothing, started the dryer and still got nothing. 

Can anyone take a stab at helping me determine if my motherboard is bad or if its a bad wiring issue or did I overlook a sensor or relay test?   MUCH APPRECIATED! My neighbors are getting tired of drying our laundry for us. 

Thanks!

[MD8012]

Did you check the centrifugal switches on the motor?

 

[getmp3s]

5 hours ago, MD8012 said:

Did you check the centrifugal switches on the motor?

No i did not - in fact it had not even occurred to me to check that since the motor is working, but now that I look at the wiring diagram, it could be a point of failure for the heater, i'm going to test that right now - thank you for the tip!  

[getmp3s]

On 10/20/2019 at 4:05 PM, MD8012 said:

Did you check the centrifugal switches on the motor?

 

Update:  After thoroughly confirming that the centrifugal switch is working perfectly i then began to trace the continuity on both sides of the centrifugal switch wiring harness for wire breaks, one leg takes me to neutral and the other leg takes me through the entire heating system which i re-confirmed at every endpoint and through each sensor, and then finally up to the heat relay on the motherboard.  The only ohms reading I got which was out of norm was across pins 3&4 (Red&Black) on the motor switch expected read should have been  2.88Ω and the expected read across pins 4&5 (Black & Blue) on the motor switch should have been 3.5Ω but for both reads I actually got 1.8Ω.  How significant is this? Motor was NOT running when i did the ohms tests. 

What would be the best way to thoroughly test the motherboard's heat relay next?

[getmp3s]

Its the motherboard relay, i just pulled the heater wires off the motherboard, jumpered them together and the heater works now, of course without any thermistor regulation so I've got to find someone who can replace the relay on the board. Samsung says they just discontinued selling this board, literally a week ago and its no longer available, repairclinic just pulled it from their site.  Arg! 

[Scottekarate]

You may try a company called Corecentric based out of Illinois. They take your board and fix it up and even have a warranty. Our store has used them many times.

[Budget Appliance Repair]

How did you check the centrifugal switch?

These have two switches that must work - the motor can still operate OK but if the NEUTRAL sense switch doesn't make once the motor has started it will not signal to the board that the motor is running so the heat will never come on.

These motors are well known for having this problem.    Motor switch contacts 1-2 for the main heat circuit can check OK but the NEUTRAL sense on contacts 5-6 can be bad, once motor is running neutral needs to feed thru 5-6 circuit to the board to let the logic in the board know for sure the motor is running.

Just jumping the heat relay on the board doesn't prove the board is the problem.

[getmp3s]

11 hours ago, Budget Appliance Repair said:

How did you check the centrifugal switch?

Thanks for the tip - I realized you were right in that I neglected to test the 5-6 contacts on the centrifugal switch, I had previously only tested and then traced 1-2 all the way up to the motherboard, but alas 5-6 contacts are working as well, and i then tested those legs up through the steam/water valves and to the motherboard and on the other leg it went to neutral.  Testing with the dryer unplugged i got continuity through the whole system (some resistance lost as it went through the water valves) and with the dryer spinning i tested AC neutral passed through 5-6 up through the door switch and to the motherboard.  I so wish the problem was my motor as that's an easily replaceable part. The motherboard is not 😞

I appreciate the tip, I will test any and all suggestions this forum can throw at me!