Thermador SEC301BB/03 broiler stays lit

[Fritz]

tired to bake at 350º the other night and had a broiled loaf after 15 minutes at most.  about 10 years old

Relay board?  Replace the whole board or can one specific relay be pointed to and replaced (if the are OTS relays and not proprietary.)

[Hiroshi]

Did the unit stop heating when you cancelled the cook cycle? or did you have to throw the breaker?

[Fritz]

it stopped cooking without me throwing the breaker or canceling the cook cycle.  Then error F33 appeared.

[Hiroshi]

Ahhhh, ok. F33 means: Upper oven over temperature detected ( while in a non-clean mode), which would make sense if the broil relay was stuck on or if you have an improper ground causing the broil element to "run-away."

Have you been able to clear the error code? (if you hit cancel, does the F33 disappear and allow you to choose another cycle?)

 

[Fritz]

won't clear.  It's a single oven, though I know the codes are the same.

Any idea which relay is the "broil" and/or which diode and/or resistors are part of its' circuit?

[Hiroshi]

Double line break relay is K4 (P12-4 and P12-2) and Broil relay is K2 (P13-1 and P13-2). I would also get a clear look at the broil element terminals and be sure they haven't contacted the cabinet at some point...

[Fritz]

P13-1 and 2 refer to pins of the relay or test points on the bottom of the card?

I put the card back in the oven for the time being.

In my photo, I notice what might be some thermal damage on D42.  Might it be a candidate?

Are the relays off the shelf?  Are they even likely culprits rather than a diode or resistor?

Thanks,

Fritz

[Hiroshi]

Well, the resistors heating and browning the PCB is totally normal in most cooking controls- so I wouldn't go after that immediately. The pin-outs are where the relays I named output at the board header connector pins... I wouldn't necessarily change the relays either, unless you can prove they are fused with your meter.

Usually the board won't just run away- if the temp probe is bad it should give you an error code before it misreads the temp badly enough to reach "self-clean cycle" temperatures, so I tend to rule out all the physical wiring issues that could be responsible before getting into board level troubleshooting...

First thing is to meter those relay pins (with the wiring disconnected) to establish whether or not the DLB relay or the broil relay is welded closed... while you are there, you can meter the corresponding molex terminal to the broil relay and one probe to the frame can tip you off to a short to ground, which can cause your symptom also...

[Hiroshi]

If your wiring is perfect and the elements aren't grounded, the next steps would be to test the temperature probes, as a matter of course, then start trying to diagnose why the computer control would "choose" to overheat rather than fly right... because the relays might be fine, but the cooking algorithm might be corrupted on the processor or there is some input being ignored, the broil element should cycle on at times during bake, but it obviously shouldn't be energized longer than the bake element.

I had a call once where the owner had swapped the bake and broil terminals on the board and was burning cakes and pizzas left and right... 

Global Micro Parts is a good place to seach for relays and board components for pennies on the dollar...

Edited September 14, 2016 by Hiroshi

[Fritz]

where are the temp probes and what do they look like?  

But if the proc has an issue, then the board is toast, say for someone who can replace a wave soldered proc …. I assume?

I'd guess it's unlikely that it could something as simple as a molex pin that has phunk on it?  But I guess I'll find that out when a replacement card comes.

I bought 1 just to be safe.  Figured, if that fixes the issue then I can "meter" around the board to see if any anomalies turn up.  If not, then I'd assume the proc?

Does any one refurbish these cards?

[Hiroshi]

Temp probes are steel tubes smaller in diameter than a pencil, approximately 4 inches long- they usually jut out from the back wall of the oven, on the upper right or left side. You can usually test them without pulling the oven from the wall by unscrewing the fasteners on the mounting flange and pulling the probe into the oven cavity until you can disconnect the molex and meter the two pins for ohm's resistance. Standard reading is about 1100 ohms at 72 degrees F

[Hiroshi]

Well, I tend to work at testing the cheaper more accessible parts before moving toward the expensive computers, but if the board swap knocks out the problem, you have your answer!

[Fritz]

true that. Time will tell.