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Shal

Control panel on Thermador C302U double-oven sparked

32 posts in this topic

My wife noticed an odd burnt smell, like plastic not food, coming from the upper oven while cooking. We emptied and looked all about the interior of the oven expecting to find some odd bit of plastic had fallen in. Then while discussing "what now" the control panel made a very loud snap and flash of light -- which tripped the circuit breaker.

 

I'm thinking that smoke and grease build-up inside the control panel may have arced over, but perhaps there's worse than that awaiting me. This occurred a week or so after running a self-cleaning cycle, but nothing appeared wrong at that time, and the oven had been used at least once more after the cleaning without incident. So I don't know if the cleaning cycle is relevant or not.

 

I have the "Care and Use Manual" as well as the Installation Instructions, but I was hoping to find an assembly drawing or other way to confirm that simply removing the obvious row of screws on the bottom side of the panel is the right next step towards repair or (likely) replacing the control PCB. The Thermador site was a bust for manuals, too old I guess.

 

Any advice for the wary but experienced DIY appliance fixer?

 

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Ok, the panel came off and disassembled as easily as I could hope for. Took pictures so I'll be able to put the cables back on the right connectors.

 

The surprise (to me) is how clean everything in there appears to be. No sign of what happened -- no scorched wires or marks anywhere. The boards in the control panel itself look fine, which makes sense because they are all logic probably, but what I can see from the front edge of the board that's just above the cleaning-lock mechanism in the center looks ok too. A little distressing that there's so little vertical room there that all the push-on wires are immediately bending 90 degrees against the sheet metal above them, but it seems ok.

11378007003_5c5bec0a9e_z.jpg

11377874215_e18e71a4b3_z.jpg

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Getting that relay board out of there for more careful inspection doesn't look like any fun at all. It doesn't look like that sheet metal that its mounted on can be removed from the front.

 

It seems like I have to pull the whole unit out of the cabinet, and then ???. Which means the doors come off first, and one of those has a broken hinge (but that's a whole other repair pending). And of course pulling it out will mean disturbing the shim-work that has it all snug and level in place. Bother.

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Grear job getting this far!  And nice pix, too.  The touchpanel lifts up from the bottom and off.  But you're really gonna want the service manual before proceeding any further:  http://appliantology.org/files/file/333-thermador-c-series-built-in-wall-oven-service-manual/

 

You'll need to be an Apprentice to download it:  http://apprentice.appliantology.org/

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Domo!

 

I wonder why I didn't get the email notification of your reply. Alas, pardon the duplicate request in the manual request forum. 

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I checked the notification settings, didn't see a problem. Interestingly I did get the notice of your quote of my "I wonder why".

 

But back to business, I notice some discrepancies between the manual (C302) and my oven (C302U), is there perhaps another manual, or an addendum? The differences have to do with how the control panel is held in place, fortunately mine was much easier to remove than the manual's description (I didn't have to pull the unit out any distance). That difference might imply differences in how the relay board is accessed as well.

 

I'll know more once I work up the courage (and focus my son's strength) to pull the unit out of the cabinet. But first some floor protection and maybe a platform (the cabinet floor supporting the base of the frame is about 8" to 10" off the kitchen floor). I'm not sure how paranoid to be about trying to lift it out and down in one go (which implies up and in in one go, later) or to arrange a platform so that I can basically take it straight out and back. The consideration is complicated by the fact that the oven is in the corner of the room, so I can't have my son stand opposite me at the side of the oven. Just how heavy is this beast I wonder. The doors will be off, of course, but there still seems to be substantial mass there.

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Spend a little time and build a platform with wheels to help with pulling the unit out of the opening..I have a furniture dolly with a piece of plywood  and some milk crates that are stack able for single ovens and just the dolly with a 2X4 frame for low /double ovens.............I keep the stand about 1 to 2 inches lower then the base of the oven, it just is easier to slip it back in later............Remove the doors, it will be a lot lighter................. Check the terminal mounting block where all the 'line in' wires are attached.... Power to the unit.......One wire could have melted the block  ( the plastic smell) and came loose and touched the frame .........If the block is damaged, there are after market blocks that will work/ take the load ..........Keep us posted.....

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Domo Sensei.

 

I have a very sturdy furniture dolly I can stack up for the purpose, I just wasn't sure whether wheels would be an advantage. But I guess if I need to access the back of the oven, or inside the cabinet, then that will make a lot of sense. 

 

You have your platform lower than the oven's base? I'm worried that will mar (crush) the front edge of the cabinet if I tilt downward across that edge -- it isn't like the cabinet is made from rock maple. On the other hand it isn't a visible location with the oven in place. I was thinking level or maybe even slightly above the cabinet floor would be safest.

Edited by Shal

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The platform on the dolly/cart is smaller than the size of the  base of the wall oven...........Say the depth of the oven is 24 inches, my platform is only 16 inches....You will be holding and pulling the unit out by the lower  opening, just pull it out till the trim is past the outer edge of the platform and set down, then wiggle it out the rest of the way.......The wheels are just to pull a out a bit more and then spin the unit around ( as far as the whip allows )  and remove all the panels to get some eyes on the wires........ ..

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Thanks for the advice on the platform, that really made pulling the unit out a snap.

 

And boy what I found on the relay PCB:

 

11494245636_fe300cc7f9_z.jpg

 

11494191404_7036481a04_z.jpg

 

So clearly that gets replaced. But I also need to replace the connector at that location:

 

11494160285_8430a1006f_z.jpg

 

And maybe the one from just left of the yellow transformer (in that picture):

 

11494182774_d07c2056a8_z.jpg

 

The relay PCB is easy, so I guess my next challenge is to find part numbers and sources for those two connectors. If nothing else Digi-Key will likely supply them, once I figure out what they are. Then comes the fun of crimping on the new sockets and getting the right wire in each location...

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I guess the other thing I should be thinking about is "which circuit is was that", in the sense of maybe things on the other ends of those wires should be inspected and maybe replaced. Interestingly the wires themselves don't appear to have been "cooked", except right at the damaged connectors.

 

I wonder just what happened to cause such damage. Did the connector go ohmic and burn away there, ultimately allowing a direct short? Funny thing is it looks like all the wires are still captive in the connector shell, eaten away though it is.

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Ok, the big damage seems to center on P1-6 and P1-8, the feed to the cooling motors. I don't see any damage to wires 94 or 23 except right at P1 (visible in the photo).

 

Disconnecting everything from the upper cooling fan motor I measure 11.5 Ohms across its terminals, and open circuit to the chassis, which seems good. Likewise measuring across 74 and 75 (the connections to the lower cooling fan motor) I get 12.2 Ohms there and open circuit to the chassis, also seeming good. No visible damage to the visible length of 74 and 75, possibly I should find and open the correct panel to visually inspect the lower cooling fan motor directly.

 

I found one thing disturbing. Wire 24, which connects the cooling fan motors back to the Neutral terminal block, measures zero Ohms to the chassis. That does not seem right. Even though there shouldn't be any voltage between Neutral and chassis ground, I think there also should not be any direct connection between them! I think that means my next logical step is to disconnect each wire in turn from the Neutral block (TS3) until I discover what is connected to the chassis.

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If someone by chance didn't install a 4 wire pigtail correctly, (didn't remove the buss bar from neutral to ground at the terminal block),  or if this is a 3 wire pigtail where the center neutral connector on the terminal block has the strap to ground you would see a direct circuit/very low ohm reading across a neutral to any ground connection.

Edited by Budget Appliance Repair

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That kind of damage is most found on terminals that connect the heating elements to the control/relay boards............I 'm downloading the service manual now...Will check the wire schematics in a few minutes.........

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Ok, cancel the concern over neutral versus chassis: disconnecting the conduit neutral wire from the terminal block broke the connection - so I was measuring the connection in the breaker panel (the only place they should be connected).

 

Still no evidence of where the current that destroyed the PCB and connectors came from or went to though. That has me a bit nervous. It didn't go through the blowers, as they're both still intact. Yet it was enough current to pop the circuit breaker with only a moment's flash.

 

RepairClinic has a bunch of items labeled "Wire Harness", but identified only by a part number, no photo. Neither the service manual nor the schematic that was taped inside the oven identify the wires by part number for harnesses. So I'm not sure how one is supposed to figure that out. But looking at the prices maybe I don't want to, I'd rather just crimp on new connectors. Under 5 bucks at Digi-Key gets me two of each.

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I pulled the back off and had a look around. Still no sign of any other damage.

 

The heating elements all measured no connection to the chassis, and nominal across each. The convection fan motors, like the cooling fan motors, measured nominal across them (one side is connected to neutral).

 

Unplugging the halogen lamp circuits at their in-line connectors measures no connection to chassis, and nominal across them.

 

I'm running out of ideas for things to check before just putting it all back together (with new relay board and connectors, of course) and turning it on to see if it blows up again. That's an expensive way to learn though...

 

There's a collection of photos at Flickr, for anyone who'd like to see the insides. I've included a couple of my platform as a tribute to certified tech group 51's good advice.

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There's a collection of photos at Flickr, for anyone who'd like to see the insides. I've included a couple of my platform as a tribute to certified tech group 51's good advice.

 

 

Nice set of pix!

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Any suggestions on testing the oven once I get the new relay board?

 

The naive option is just to button it all up, slide it back into the cabinet, put the doors on, and pray. I'd rather have some assurance before going all that way.

 

One thought is to defeat the door switches and with it still out on the platform run it quickly through enough settings to see that each part is working. Probably a good idea to put the back on and the other panels I've removed, just so that anything that might happen is contained.

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Only button it up as much as necessary until completely tested. Make double sure that no wires or connectors are touching ground after you finish your repair. Once you're ready, flip the breaker and test her out!

 

You more than likely just had a loose connector or wire - MAKE SURE ALL SPADE CONNECTORS ARE NICE AND TIGHT. If any loose connectors, replace.

Edited by acfixerdude

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Awesomeness. The oven is still out on the platform, but I completed the installation of the new relay board, including replacing the burned up connectors, put the front panel back on -- and it works. No acrid smoke, no spark. Just a very large room heater (the doors are still off).

 

Next a quest to replace the lower oven air-flow switch so that at long last we can also use the lower oven (we've had code F64 for some years now). Ohm meter says that switch is only sporadically making contact when the arm is pulled back. Switch for the upper oven seems ok, (as it must be since I don't get any code F34s...).

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Wow RepairClinic, $44 for a microswitch?  Normally I don't begrudge services like theirs the extra coin for having the right part. But in this case I think I'll go with this $5 one instead:

http://www.digikey.com/product-detail/en/E22-85HX/CH341-ND/280885

 

Of course, that does mean I'll have to kludge my own paddle onto the lever arm, but I imagine I can just cut the one from the old switch.

 

I've uploaded some new photos, including the door tear-down (I scrubbed clean both sides of all three sheets of glass in the upper door, since I had it apart to replace the hinges anyway), the replacement of the circuit board, the new connectors, and the identification of the microswitch. Also the free-standing oven as an oversized room heater. You'll find them at the end of this set:

Well, there's your problem

 

Or start here and click the right right arrow on each picture:

http://www.flickr.com/photos/shalf/11924548823/in/set-72157638683208186/


Oh cool, I didn't know the link to the photoset would automagically turn into an inline slide-show.

 

The things these web designers think of...  ;-)

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Nice Pix!   Great job on the repair!

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Well, rats. Even with the new switches installed, the air flow on the right (lower oven) side is too feeble to actuate the switch. So the lower oven still codes out (F64). I checked that the switch moves freely and isn't rubbing or hung up on anything.

 

There is a very noticeable difference between the robust blast of air coming from the left (upper oven) side and the gentle breeze on the right. Looking through the air entrance between the ovens I can see that the lower blower is turning, but I can't really judge how fast. With the rear cover off I can spin the blower and it appears to spin freely so I don't see any reason it shouldn't produce normal air flow. With the back cover in place and the oven operating (during the timeout period) I checked around the panels and didn't notice any significant leakage of air escaping.

 

The one thing left is that my oven does not have the air diverter shown in Figure 24 of the service manual. But the fact that such a thing was retrofit to the ovens suggests that the lower oven's cooling flow is known to be less robust, and that my blower isn't faulty (per se). I didn't have any luck finding that bit of metal, part #16-10-101, at RepairCenter so Sears may be my only hope short of fabricating one. I think I can adequately guess at suitable dimensions, but if anyone can come up with the dimensions of the official part I'd be grateful.

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AppliancePartsPros indicate they have them, but out of stock......................Parts store.com...Again out of stock.....................About 50 Clam$.......... :thumbsup: ........

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