Microwave Oven Failure: Spontaneously turned on… by its LED display

My microwave oven started to malfunction at around five years old. It started to randomly power on the lamp, fan, and turnable. It progressively got worse over several weeks until it was mostly stuck on. The microwave oven is not usable when this happens: It behaves as if the door were open, causing the control panel to ignore button input and to stop cooking if it was cooking. The obvious suspect is a failing door switch, but was not the cause of this failure. The microwave “turning on by itself” was caused by an aging/failing LED display. Yes, really. . . . → Read More: Microwave Oven Failure: Spontaneously turned on… by its LED display

Depstech DW49 Webcam — Teardown and Measurements

The Depstech DW49 is a low-cost webcam that claims to record 4K 30 fps video. I recently got one “used” from eBay for $30, so I can find out what’s inside by disassembling it and making some measurements.

“4K” cameras at this price point often use a lower-resolution image sensor and then scale up the image to 4K, resulting in a video with the right number of pixels, but a blurry picture. The DW49 also upscales 4K video (8.3 MP) from a lower-resolution sensor region (5.2 MP), but the difference from reality is less than some other “4K” cameras I’ve seen, and is a step up from Full HD (2.1 MP). Overall, not quite as advertised, but not bad for the price.

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Windows 9x TLB Invalidation Bug

In processor architectures that support paging, there are usually one or more TLBs or pagewalk caches to cache address translations. On x86, these translation caches are not coherent with memory accesses that modify the page tables, and need invalidating after a page table entry is modified.

The Windows 9x kernel contains code that modifies a page table entry, then immediately uses it without an invalidation. This causes crashes if the processor strictly follows the instruction set specification and does not provide pagewalk coherence.

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