Calore Z1362/R1 waterbed heating controller repair (#P30)

An emergency repair from last Friday night, you know, the ones with the deep green WAF that could offset all your wrongdoings of the entire week if there were any…

I’ve been sleeping on a waterbed for 12 years now; it was the first major (read: expensive) thing I bought after I started going to university. Sleeping on a sofa bed doesn’t really work long-term, but that’s what you do as a broke student with no family to step in. Said waterbed sprung a leak earlier this year on one of the corner seams, so the inner mattress part got replaced (plus the worn topper). Pinholes on flat surfaces can be repaired, but this was on a delicate, ever-moving piece. That’s about the only issue I had with the thing, certainly worth the money for getting rid of all the back pain from childhood and adolescence in an instant. “Luxury” until you try it, eye-opening when you do.

On Thursday, I dozed off on the couch and switched to the bed in the very early morning, but something was off. I was cold and even raised the temperature of the bed (with a few controller hiccups), but I didn’t really sleep all that much for the rest of the night. Friday I went to bed early as I tried to catch a colleague at work on Saturday who only was there till noon. Bed was stone cold. FUCK.

Clues:
* Display contrast faded away years ago
* Chilly feeling on one day last week as well, so probably intermittent failure
* Controller loses entire display after a certain time, but a power cycle restores it
* Lowest power design, always-on at about 0.4 to 0.6W at 0.2 power factor (plus heating, 200kWh/a at current estimate)
* PTC heater mat seems okay with 370Ω across the two center pins of the 6 pin connector (other ones unknown)

Well, it’s not really a teardown with three outer and three inner screws, so skip that. The PCB is designed around a Samsung 3P9228AZZ-QZ88 QFP-44 chip (8 bit CMOS microprocessor according to the Interwebs) with three tacky feeling buttons and some timekeeping auxiliary stuff that feeds an ST T1235-600G triac (600V, 9A) for actually controlling the external heater mat. A QFP-44 seems overkill for that task, but maybe that’s just a shared part with upmarket controllers that do more fancy stuff than just automatic or time-controlled heating.

And as this one is fed 5V with lowest possible part count and heat dissipation, the culprit is on the front of the PCB: The X2 capacitor that makes the capacitive dropper work. Classy Tai-Yao brand with fake CE sign, 220nF/275V MPX.

That one measures 55nF in-circuit and also desoldered, which equates to 1/4 of design capacity and similarly lower power delivery to the processor. No wonder the chip craps out over time, but does respond to a hard reset. Display backlight is still present, but it has always been very dim to not disturb at night – LEDs can do with sub-milliamps.

The other guy in the photo is the Hitano branded 2200µF 6.3V 85°C smoothing cap, which I replaced (for good measure) with slightly better Samwha cap (2200µF, 16V, slightly longer form factor at same width). That one read over 3000µF desoldered at a huge loss factor, so it’s close to drying out but would have worked for another few years probably.

After replacing the X2 cap with a Wima MP3-X2 220nF 275V cap with same spacing but slightly higher case that I had in my parts bin, I took some more photos, screwed it back in place, and went back to the mains plug in the bedroom. The two caps rubbing against each other should be no issue, as the Wima insulation layer is pretty thick.

The angled plastic spacer unit of the display keeps the LCD module pressed flat against the front of the unit, otherwise the pressure of the zebra strip would tilt it. I guess this is a slight manufacturing mishap, as it is really pressing down hard and a few tenths of millimeters more spacer height would make a much better fit.

What can I say – works as expected, display contrast like new. Cost of the Wima X2 cap would be 1.05€ plus literally pennies for a run-of-the-mill 2200µF 6.3V+ electrolytic, but both were available from my drawer.

Here’s a quick comparison shot of the cooled down bed a couple minutes after installation of the fixed controller vs. the next morning. Same 10°C to 20°C color gradient span. Doesn’t look like that much of a difference, but every Kelvin of temperature difference makes the bed a significant better(worse) heat sink in both winter and summer conditions. Plus the hot spot on the left was were I sat for plugging it in. But what can I tell you about fine-tuning a waterbed, I’m the princess on the pea that can spot a 250ml filling error (out of ~600l) by an aching back :)


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