Repairing Mr. Coffee

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.

Heating element from Mr. Coffee

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.

Mr. Coffee PC board, bottom

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.

Center-tapped power transformer from Mr. Coffee

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.

Mr. Coffee interior rewired to bypass PC board

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).

Mr. Coffee PC board, top

User-interface side of the control panel PCB.

Mr. Coffee PC board; edge view showing IC as display standoff

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.

1990s Mr. Coffee control panel, front

Larger all over. Brown instead of white. Vintage.

1990s Mr. Coffee control panel, back

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.

8 Responses to “Repairing Mr. Coffee”

  1. ppvi says:

    LOL on the standoff IC.

  2. Sean Weatherford says:

    Some consumer electronics have a power transformer with a single turn of smaller wire used as a fuse on the primary side. That is the cause of death in most cheap transformers. It is usually on the outside layer and can sometimes be fixed.

    The standoff IC is fun stuff.

  3. Keith Neufeld says:

    Sean, thanks for the transformer information — I definitely didn’t know that! Any ideas on sizing replacement wire? Or just do without, maybe adding a separate fuse?

  4. Garrison says:

    A part came off from behind the coffee pot near where a tab with a spring is. There is also a flipper hanging down. The part i Have in my hand is sort of concave with 4 pins or pegs. I can’t figure out how it gets inserted given its proximity to the spring and the flipper. Thanks for your help.

  5. Keith Neufeld says:

    Garrison, I’m not familiar with the parts you’re talking about; but if you post a picture somewhere, I expect someone could look it over and give you a hint.

  6. BIll Winans says:

    I have a JWX27 Mr. Coffee, two now, that the various small indicator lights go wacky, then a few brews later it stops brewing. Both after about a year. Funny we have old ones small and ugly that work after 20 years! would like to get these working. Has a removable PC board, and leads are detachable. I do not have the electronics experience or tools to check it. would like to get a replacement part and try a bit of process of elimination. Not soure I can safely just by pass the board all together. Any ideas? Bill

  7. Henry Priebe says:

    What I’d really like to find is a hack that would extend or eliminate the 2 hour warmer timer on newer Mr Coffees. I have developed a reflex to hit the power button twice when I pour a cup of coffee so the shutdown timer resets. A pot of coffee frequently lasts me 4 hours and sometimes up to 6. Unfortunately that power reflex also sometimes kicks in for the last cup of the day, resulting in a somewhat scorched carafe.

    Oh and Garrison, that part sounds like the filter basket shut off actuator lever that snaps into holes in the bottom of the basket with only two of the pegs so that it pivots. When the coffee is brewing and the carafe is on the warmer it pushes the spring up unseating the valve to let coffee flow and when you remove the carafe while it is brewing it halts the flow of brewing coffee until you replace the carafe on the warmer.

  8. mr coffee bvmc-sjx33gt electrical wiring diagrams is what I am looking for. On the inlet side of heater assemble is a round disc with a blue and brown wire going to it. A good amount of white power has come out of disc. Can I replace it?.

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