LG LST5651SW stove: oven not heating properly

[R_J]

Re: LG LST5651SW stove: oven not heating properly

Since the top element (broil) works, I would suspect that RY6 is bad.

It may or may not be getting told to turn on but to check that it would require working on a live oven.

You could give the smaller relay a couple taps with a screwdriver handle and see if the bake element comes on, then you know the relay itself is bad.

[redwire]

Re: LG LST5651SW stove: oven not heating properly

From the pictures: Everything looks OK, board soldering has a few rough spots but no big fractures. There is no thermal safety switch in this model.

I do see a blackened diode with splat of solder, on the relay on the right. I'd look to see if the relay spit some molten metal or what. Both diodes should look identical.

RY6 is Bake, RY5 is Broil, RY8 DLB is the safety relay for both.

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

Here's the sheet of diagrams.

[R_J]

Re: LG LST5651SW stove: oven not heating properly

The connections look ok. That leaves the relays, so either the relay contacts are burnt and not closing OR the coils are not being energized (turned on). I would suspect the smaller relay (RY6) could be bad as it connects directly to the lower element

Is this wire (red arrows) all connected to the same point (red ac line in)?

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

The two black plastic relays are marked Potter & Brumfield T9AS1D22-12.

The solders look good to me. They are all shiny and reflective though the photo doesn't capture that. Some have a dull spot in the middle.

[R_J]

Re: LG LST5651SW stove: oven not heating properly

Is that it on top left of the board: 6870WIN12A?

NO, on the black plastic relay itself. but I think I figured out the pinout
Have you removed the board and checked the solder connections?

It looks like the smaller relay (RY6) is the one that controls the bake (lower) element

Does that sheet diagram show how the elements are connected to the relay board?

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

The first thing I would do is inspect the solder side of the relay board for poor solder connections on the relays

Can you provide the part number off the relay?

Is that it on top left of the board: 6870WIN12A?

[R_J]

Re: LG LST5651SW stove: oven not heating properly

The first thing I would do is inspect the solder side of the relay board for poor solder connections on the relays

Can you provide the part number off the relay?

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

Post pics of the relay board backside, I suspect a intermittent connection to the bake heating element or a bad relay.

Here are photos of the back and a close-up of the relay board.





I marked the relay board photo with three red lines. Any combination of these test OK for continuity. Of the six connecting posts on the board, no other combinations test OK for continuity. If that means anything...

Please excuse my ignorance. I have pretty good common sense, but little electrical/electronics knowledge. I'm learning as I go.

The big sheet that was attached to the back of the stove has diagrams but doesn't mention a test mode, only instructions to test for continuity, and what the ohms reading should be for all the components.

How do I properly test the relay board?

[stj]

Re: LG LST5651SW stove: oven not heating properly

Yeah that's an old trick of seeing a millivolt voltage drop across a wire or fuse which indicates current flow.

no, i'm talking about creating an induction coil to obtain some mV based on the current flowing into the heater

[R_J]

Re: LG LST5651SW stove: oven not heating properly

Most ovens will turn on both the main element and the broil element to get the oven up to temperature faster (preheat), In this case it seems that only the broil element is being tuned on to get the temp to 365, If the lower element is not operating it is either open or not receiving any voltage.
Locate the relay board and check it.

[redwire]

Re: LG LST5651SW stove: oven not heating properly

Yeah that's an old trick of seeing a millivolt voltage drop across a wire or fuse which indicates current flow. We don't know if there is power to the bake heater or current flow when the oven is hot and craps out.

Hey, I looked a bit more and apparently LG ovens have thermal limiters (fuse) i.e. https://www.reliableparts.ca/product...al Safety Fuse
OP, can you post a picture of the back wall of the oven?
You would be able to see one of these, or spot bad connections etc.
Usually a bad connection or relay contact will make heat and burn/melt things as well as a zzzzzzt sound. They can stand out.

edit: there was an LG recall for this stove. "The burners on the electric ranges can fail to turn off after being switched off or the temperature setting can increase unexpectedly during use, posing burn and fire hazards to consumers. To determine whether your electric range is being recalled, please follow the instructions below."
https://www.lgelectricrangerecall.com/

[stj]

Re: LG LST5651SW stove: oven not heating properly

wanna try something questionable?

in theory if you wrap a few turns of insulated wire around a power cable and then hook the ends to a voltmeter it will show current-flow as volts.
but i dont know the turns-ratio so you could get mV or you could get much higher

[redwire]

Re: LG LST5651SW stove: oven not heating properly

It sounds like there's simply not enough heat to get the oven past 365° with only the broil element puttin' out.
As was mentioned, the bake heating element (or relay circuit) could be going bad, open-circuit when it's hot.
You're going to have to troubleshoot it. I could not find the LG service manual which has a test mode and wiring diagram to make repair easier.

Post pics of the relay board backside, I suspect a intermittent connection to the bake heating element or a bad relay.

The temp sensor if bad will show the wrong temperature or an error code. It looks fine. A multimeter continuity test is for wires and connections, readings under 100 ohms beep so it's normal for a thermistor to fail a continuity test at 1,000 ohms.

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

More info:

No error code shows on the display. On the product sheet, there's an error code table, with "F7 Main oven heating error" that covers both oven heating elements, sensor, and PCB.

It seems to get up to around 365 and stops. I'd been setting it to 400 450 to test. Now I set it at 300. When it gets to 300 and the preheat complete alert -- beeping and flashing oven light -- goes off as normal.

[redwire]

Re: LG LST5651SW stove: oven not heating properly

LG LST5651SW Parts with 6871W1N012B oven relay board like https://www.reliableparts.ca/product/inv_16906185
You should be able to hear the relay clunk, or swap the wire with the bake/broil heating element.
edit: weird the board shows no "BROIL" spade terminal, even the 6871W1N012A with extra relays doesn't show it.

I would do a visual for bad solder joints on the relay board, including the connector to the (other) oven control board.

[R_J]

Re: LG LST5651SW stove: oven not heating properly

It looks like there is a oven relay control board in this stove, I would check the relay solder connections, then check the relay operation.

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

I removed the element. There's no damage, corrosion, anything like that. It looks perfect. There's no visible damage and the resistance is to spec -- does that mean that it's fine?

[petehall347]

Re: LG LST5651SW stove: oven not heating properly

you could check the voltage is getting to it

[Curious808]

Re: LG LST5651SW stove: oven not heating properly

you metered the element cold, it could go open as it heats.
put a high wattage lamp in series with it to see if it draws current continuously
or use a clamp-meter

I don't have either of those. Is there another way to check?

I haven't actually removed the element, only disconnected the wires. Would I be able to get a more useful reading if I plugged it back in and turned on the oven for a few minutes before testing? Or if I removed the element, would it likely show physical damage?