Bad microwave PCB?

Thread Starter

Brian L.

Joined Oct 21, 2022
3
Recently my microwave would shut off after only a minute of operation. Shut off as in a complete shut down of the machine-no power to the display and the buttons were inoperable. After unplugging and then re-plugging in the unit, it would work again but only for about 45 seconds and then shut down again. after removing it, opening it up, and safely discharging the high-voltage capacitor, I determined there were no issues with the fuses or the high temperature thermostats. Given the erratic nature of how the unit shut down repeatedly and now won’t even turn on beyond a single blink of the display, would I be correct in assuming the PCB needs replacing? Any other suggestions?
 

MisterBill2

Joined Jan 23, 2018
13,798
With some other electronic devices that sort of problem is caused by slightly defective electrolytic capacitors. So using the principle of guilt by similarity I suggest examining the various higher value capacitors.
And understand that this is an analysis based on the similarity of symptoms, given that I have not even see your microwave oven. It might have a high frequency inverter to crreate the high voltage, instead of the heavy transformer. Like the Panasonic inverter microwave ovens.
 

Thread Starter

Brian L.

Joined Oct 21, 2022
3
I did a cursory check of the capacitors and didn’t see any telltale bulging or other failures, but I can test them. This is a LG microwave and most certainly has a heavy transformer.
 

WBahn

Joined Mar 31, 2012
27,894
Can you get a replacement circuit board? If so, how much does it cost? Sometimes, the cost of a new board, if available, is low enough that you can't justify the time to even figure out of the old board really is bad. Depends on how much your time is worth to you and how much you enjoy trying to chase things like this down.
 

MisterBill2

Joined Jan 23, 2018
13,798
On my Panasonic Inverter microwave oven there have been several failures to function, and each time they were mechanical, caused by incomplete motion of the mechanical parts in the complex door latching mechanism. Evidently all of the good engineering was in the electrical portion, and the mechanical part was not designed very well at all. It did get through the warranty period with no issues, but then the mechanical problems began.

There are three switches interlocking the door to assure it is closed and latched before it can heat. One switch iss are in series with the AC feed, one shorts the AC until the door is latched completely, and one is tied to the control circuit board. That is the one that does not operate until the release button pops out all the way. Which does not always happen. POOR mechanical design, or poor assembly, not certain which it is.
So one thing to examine is all of those interlock switches. It might be a contact opening a bit after it heats during use. Those can be a real dog to diagnose.
 

MrChips

Joined Oct 2, 2009
27,686
From the information you have provided I am considering one of two possibilities (1) a faulty power supply board and (2) a faulty interlock switch or sensor.

I would take the easy path first, to see if it is a faulty interlock switch.
Since it would appear that this is an intermittent problem that has gotten worse over time it would be difficult to diagnose and pinpoint. If it is now dead then that would be easier to locate. Try to find an interlock switch or sensor that is in the fault condition. Having access to the circuit schematics would be a great help.
 

MisterBill2

Joined Jan 23, 2018
13,798
.Many microwave ovens have the circuit schematic inside, Those are the units deemed by the manufacturer as being worth repairing. Those without the circuit are evidently considered not worth repairing.
I do support the "right to repair" concept completely.
 
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