- 2025
- Jul
- 8
An easy fix for this GE Microwave Oven.
As the great Monty Python’s Flying Circus once told us: “And now for something completely different.”
This is some unknown model of GE Microwave. It’s from the early 1990s, and was originally installed in a camper van that a relative is scrapping. Since the unit didn’t get used a whole lot, I took it home thinking that it would work great for an office microwave. There’s probably a model number on the information packet taped to the cavity, but I didn’t care enough to open the now-fragile paper envelope.
Well…not so much. This is what I saw when I plugged it in:
There’s a lot of things this could be. Disclaimer: I used to work as a factory depot tech at GE, and saw this thing’s cousin boards (we just did the controls, repair centers or field techs did the actual unit.) Depending on how much a replacement board cost, some came back to the depot, some just got a new board with the the tech being instructed to toss the old one. As I don’t recognize this particular configuration, this was probably in the “toss it” category.
Background
This particular unit was branded GE, but was made by Samsung. To the best of my knowledge, GE didn’t make any of their own microwaves. (Perhaps a few early ones.) They had other companies make them - in particular, Matsushita and Sanyo did many of the 1970s and 1980s units, with Samsung picking up in the mid 80s and going into the 90s, when I left the company. There were a few others in there, including one Mexican-made unit that was built on GE Coshocton circuit board.
Samsung had the lion’s share of these devices, manufacturing, packing, and shipping the units in GE-marked boxes right to the warehouse. GE never saw or touched these things.
This particular unit was very cost-reduced. GE had been pushing Samsung hard, and it showed in certain components on the board. Displays went from Japanese itron and Noritake oil-based paints to cheaper water-based paints (that’s why you got units where the fluorescent displays were bad after a year,) PCB itself was the absolute thinnest thermoset resin that would crack if you looked at it wrong, and relays - oh boy, these were absolute crapola. No more good Aromat relays, these were cost reduced to the point where someone saw a relay once and said “I can do that!”
Relays
There are, at minimum, a couple of relays in most microwaves. Some used triacs instead, but relays are cheap and isolated. This particular unit has two relays, one for the magnetron and one for the “everything else.” It uses these relays:
The previous generation of relay was typically Aromat or Omron. These were good Japanese relays with contact surfaces that were machined in some way as to suppress arcing and extend the life of the unit, as these were often switching 10A. Not these junkers - they were simply copper buttons on an arm, and they would arc. It wasn’t unusual to get a control board that didn’t operate - it was stuck on or didn’t work at all. The relay was usually melted closed, or had so much carbon on it (and melted surface area) that it wouldn’t close anymore. I don’t have exact numbers, but we went through these relays like they were free cookies.
My boss, the shop manager, asked the project engineer about these relays. Project engineer said that they received several samples direct from Samsung and they worked great, he wasn’t sure why they didn’t work here. Boss asks if he bought them through retail channels - no - so Samsung probably hand-picked these test units. We’d constantly get ones with different names on them. Young Reem, Star, DEC, etc…I remember seeing at least 6 types, so who knows where they were actually coming from. They just looked and felt bad.
What does that mean? Any microwave that used these was born to fail. This one, fortunately, has limited hours and a lower power magnetron, so the contacts haven’t blown themselves apart. Yet.
Diagnosis
When I first plugged this thing in, it’s “uh-oh.” There are several problems that could cause this kind of display, including:
Bad resonator (clock)
Bad microcontroller
Bad power supply
Bad soldering
Cracked circuit board
Something in the display/keypad lines
These units were better at soldering than some of their earlier brethren - those were terrible and you’d often get cracks in the board, cracked solder on the transformers, bad solders on the micro and resonator, or no-solders. I can’t count how many no-solder units I got on my bench, with a couple being that way because they had enough flux on them that the board was completely gooey with it.
I almost immediately eliminated the resonator and micro because I could see the scanning of the diplay in the camera’s preview. That means it was still driving the display properly, and not just in a locked up state.
A quick look and the board and soldering on this one look ok, including the resonator. I was getting ready to check power when I noticed the ribbon cable for the keypad just didn’t look quite right. I undid the connector, pushed it around a little, and closed it.
The keypad and display can share lines on the micro, so if one is bad the other can be bad as well. The keypad in particular is a ribbon with carbon contacts that slides down into a mating connector. The connector then has a plastic blade that goes into the body and pushes the ribbon against the contacts. These connectors are garbage, they will break at their hinge and change shape slightly over the years. As this sat in a camper van, hot, cold, hot, cold…the ribbon wasn’t seated properly.
This isn’t the best shot, but you can see the ribbon coming around from the front of the keypad into it’s connector. This one didn’t break when I opened it(!)
It doesn’t take long to test, so I plugged it in and was rewarded with the power-fail all segments on display. Keypad works now, I was able to set the time:
I put it back together, gave it a test, and it made much happy hot water.
That was an easy fix - I was worried some unobtainable part (like the mask-programmed microcontroller) was dead, but it’s not. Off to the office with you!