A few weeks ago, my wife’s coffeemaker quit working, and this became A Problem. Not too long after that (or should I say, slightly too long after that) I opened it up, found I couldn’t easily fix what was wrong, and hacked it to bypass the broken part.
The symptom was that it wouldn’t power on anything — not even the timer display and the power LED. I suspected that something must have failed on the control PC board; but just to be thorough (and because they were easy to get to), I continuity-tested the thermal switch and the heating element first. No problems there.
Next, the circuit board. On the back side, which is visible inside the machine, you can see where the incoming AC power’s hot leg connects on the right, the neutral on the left (the spade connector for the AC power actually has an extra tab to piggyback the spade connector to the heating element), and the switched “brew” connection to the heating element in the center just to the left of the relay.
The power transformer is wired directly across the unswitched AC line — when the coffeemaker is plugged in, the power LED and timer display are on. I should see a low resistance across the black leads of the transformer primary — and I didn’t. It’s completely open — something happened to melt or disconnect a connection or coil wire on the primary side of the transformer. I haven’t seen bad transformers often — I’d expect the electronics to go out first, and I’m using an awful lot of em dashes in this paragraph — but electrical storms do wreak havoc with equipment in this part of the country and this part of the year.
So lessee that transformer and look at getting a replacement. Looks like an E93144 LR59375 … available online? Er, nope. Okay, Digi-Key? Nope. Digi-Key technical support for a cross-reference? Ah, nope some more. Okay, just a replacement transformer with the same specifications? Well, it’s a, uh, it’s center-tapped, it’s, it has the voltage stamped on it, it’s … it’s a blob.0V 100mA center-tapped transformer. That’s it.
What. Is. That. Blob. Looks like “8″ but “9″ would be more common.
Not expecting to find a “Mr. Coffee replacement power transformer,” I did some more web searching anyway. Nope. I had a couple of Mr. Coffee timer boards that I had bought from All Electronics in the late 80s or early 90s, but I couldn’t find them. Maybe they still sell them? Nope. Alltronics? Nope. Anyone else? Nope. eBay??? Yup! For only $8 + $8 shipping I could get a whole new control panel. Yeah, that’s worth it, given the low cost of a whole new coffeemaker. Nope.
Ooooh, but one of the auction pictures has a closeup of the transformer! In lieu of my copying the seller’s picture without permission, let me direct your attention to the above link, picture #4. Looks like an 8.0V center-tapped transformer, n’est-ce pas?
Okey-day, the next time I order from Digi-Key I can scope out a replacement. Meanwhile, tick-tock, tick-tock, the caffeine clock is ticking.
How ’bout a little rewiring to bypass the whole control panel. Since my wife doesn’t use the autostart timer anyway (she believes that leaving the coffeemaker plugged in while she’s not standing there watching it will cause it to burn down the house and make the earth disappear into a black hole), it suffices perfectly to short-circuit things a bit. New rule: When it’s plugged in, it’s on.
That’s a male-to-male spade plug jumper cable sleeved in clear heatshrink to protect it from the kind of short circuits I don’t want to have happen. Easily undoable if I ever get a replacement transformer — just cut off the heatshrink and pull out the plugs.
On the other hand, caffeine wifey says she doesn’t care about having the control panel work again. When I have a little more time I may wire up a power switch and a blank control panel with a power indicator LED so we can see that it’s on.
The Guts, Man, the Guts!
In true Keith tradition, je te presente the rest of the inside of the machine (which amounts to the other side of the circuit board).
User-interface side of the control panel PCB.
I love this — the display driver IC is used as a standoff for the display. What fun!!!
Surplus Control Panel
Found it later that day.
Larger all over. Brown instead of white. Vintage.
And otherwise very similar. I might even be able to squeeze this transformer into the modern one, if I cared.
The old one appears to have separate controls for “BREW” and “WARM,” whereas the modern one uses the same heating element for both. Mildly interesting.