OK, story time... my mother and I have had the same microwave for a remarkably long time. It is a Sharp Carousel II, model R-5A84. It is so freaking old that when I called Sharp to try and get a replacement door-open button (it has one of those great whacking rectangular plastic buttons for that... alas, the thing is held in by a pair of tabs, one on either side, and of course the tabs have long since fallen off -- so when one shuts the door enthusiastically, if one is unaware of the need to hold the button in, both the button and the little spring behind it go flying across the kitchen and Mom and I have to take the place halfway apart to find 'em) they said the model number was not in their system.
I'm not terribly surprised. The little sticker on the inside wall behind the door, says it was manufactured in May of 1993.
About a year ago, the bulb went out inside it... it's a 35 watt T8 (?) bulb, by the looks of it, which seems to be completely unavailable anyfreakingwhere in the US... go figure. The best I can find are 25 watt ones. (Anyone here that runs a lightbulb shop and is willing/able to help... let me know!)
However... a few weeks ago, a bigger problem made its presence known. I had bought a Michael Angelo's baked ziti with meatballs "family size" frozen as an intended dinner treat. (We were somewhat unimpressed, but that may have been due to what happened during cooking...) Directions indicated, IIRC, that it could be cooked entirely in the microwave, on full power ("high") for approximately twenty minutes. I'm not quite sure how far it got... I wasn't watching at the exact moment... Mom and I reckon, though, that given that the dish was basically fully cooked, it must've gotten pretty close.
Alas (as you can probably guess by the wording of most of the preceding paragraph), there was, suddenly, a loud and coarse buzzing noise and the microwave cut off. The display was blank and the buttons of course had no response. Resetting the breaker predictably didn't do much.
"Farewell, Johnny, we knew ye all too well," I guess is the applicable phrase. (...or, maybe, since I do seem to be something of a Trek nerd... "It's dead, Jim!") 1993ish to 2019... well, I can't say we didn't get our money's worth...!
Opening it up and doing the requisite spelunking somewhat later, I discovered that the control PCB, a single-sided board, had several notable features... the entire thing, including the display (a freakin' VFD!), almost-squishy no-travel awful awful awful flat membrane keypad, relays (two), everyfreakinthing, was all controlled by a single chip. Of course it's an in-house part with no datasheet available, but hey what else is new. The power supply appeared, at the time, to be a very simple switcher based on discrete components... and, oh dear, part of it had clearly overheated enough to make a sunburn mark on the PCB, and probably that's what killed it.
Looking closer now, I see that the power supply is not quite as I had categorized it. It is indeed based on a decently hefty transformer and a discrete four-diode full bridge rectifier (I can hear BigClive quoting ElectroBoom in my head as I type that, lol), but the fact that there are a bunch of zener diodes and resistors in key places tend to suggest that this is probably not a switch-mode anything. I don't want to further heat-damage them -- is there any even remotely respectable way to test them in-circuit?
I should note, I have a couple multimeters and (FINALLY!) one of those multi-component testers based on an ATMega and a cheap LCD from eBay, if that can be rigged up somehow... multimeter selection includes: an old Radio Shack analog with IIRC somewhat faulty leads, a yellow Sparkfun meter from shortly before the Fluke stupidity (it has something slightly wrong with it, though, the buzzer doesn't sound right), an appallingly cheap generic meter bought on a whim from an Ace Hardware for $10 to see just how awful it was (answer: shockingly so, it has neither fusing nor a peizo sounder, despite claims of both on the casing), a Radio Shack autoranging digital meter that someone on a PC forum up and gave me, and (deep in the bowels of my closet somewhere) a Fluke 8000A that I bought basically because I thought it would be cool to have.
Tomorrow I'm going to try and pull the transistor I think is largely responsible for the sunburn (it's a 2SB910M) and see if I can get that into my multi-component tester, see what it says... I'm pretty awful at desoldering parts, though, so this almost certainly promises to be entertaining in some distinctly unfortunate way. I have tested the transformer, it's fine, and I've tested a fat resistor next to the transistor, that's in the scorch zone, and it's fine... so I think it's probably that transistor.
*BUT.*
There's one other part, and it deeeeeeefinitely needs replacing. It's a small sky-blue box next to the chip, two leads, and after prying off the large blob of hotsnot all over it and around it, it's uhm loose. The leads are securely in the board, *they* haven't worked loose... whatever's in the box, however, has. The only writing on the box at all is on the top. It says "600B" and what looks like a logo, a sort of cursive "W" that reminds me a little of the sign over every Walgreen's in America. The silkscreen marks it as "CF90". I kind of suspect that it's a film capacitor of some sort, but I'm honestly not sure and I don't know enough to source a replacement. I've attached a photo of it to the end of the post -- not a good photo, though, sorry -- I am by no means a photographer!
But if someone can tell me what this little blue box is, and what I can (and can't) replace it with -- well, I mean, I know it's probably not the TARDIS (lol) despite the description there, but that's really about as far as I've gotten -- I'd be much obliged.
Especially if other someones can also nudge me along with the rest of the job...? Advice and responses to the other questions is not only welcome, it's encouraged.
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