Annoying Clock on Microwave

Sorry, my email addy doesn't show it, but I'm in Australia. I've verified that timing codes are NOT sent by ANY networks here. More so, of the few that knew what I was talking about, said they had heard of it, but no, they did not, and never will support it.

That was about a decade ago while digital terrestrial TV was still a bit experimental here, but even then, I don't know of any digital PVRs today that maintain time that way. There's the odd one out that does NTP if they're 'net connected, but everything else relies on standard crystal clocked circuits. Probably a bad example though. At that that level of complexity, no-one in their right mind would go to the trouble of mains-locking a clock, when implementing a single-chip Real Time Clock is so much easier. Especially so when RTC functionality is built into other multi purpose chips.

I suppose this comes down to the question of is mains locking "good enough"? Since I can't get a clear answer from anyone, I'm staying with crystals or NTP where applicable.

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OUCH! Got my floppy caught in my PKZipper!

At this price-point, there is no "CPU" to look for. They're all Chip On Board designs (the black blob on the PCB itself).

The resonator would be a separate component, and I wouldn't think that an RC oscillator would be good enough to keep mere minutes within a day anyway.

Besides simply replacing the resonator probably wouldn't show any significant improvement. You'd need to go all out and use an upper-market crystal, associated oscillator (with fine tuning) and drive the clock that way. Would likely need some divider in there too if you can't match the frequency otherwise.

And now you're starting to lean into the "not worth it" territory.

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No matter where you go, there you are.

Are you sure? I haven't repaired enough modern microwave ovens to even have an opinion, but I have yet to see such a PCB. The problem is that there are usually a mess of wires that need to connect to various components in the microwave oven. Handling a black glob PCB usually breaks the wire bonds. Black glob boards are usually more suitable for enclosed devices and robotic assembly such as calculators.

I also gave myself a Google Images tour of "microwave oven PCB" and variations. There were only about 50 assorted images of such PCB's and none of them showed a black glob.

They're available in surface mount packages and are difficult to distinguish from a large capacitor.

I beg to differ. It's probably off frequency for some reason, and would bring it closer to acceptable. 120 seconds per day is lousy. 40 seconds per day might be a little less lousy.

Yep. However, if the CPU can be identified, the data sheet usually has instructions for using the internal clock oscillator with either crystal, ceramic resonator, or external input. At worst, it would involve also changing 2 capacitors.

I've been there many times. I'm one of those compulsive repairmen that insists on fixing things, even if they're not profitable. Personally, I like the ceramic resonator type real time clocks because when the power dies, and if they have a backup battery, they keep running. Unfortunately, most microwave ovens don't even have a big capacitor to keep the time during minor power interruptions, so it's kinda a wasted preference.

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

"John Tserkezis is a MASSIVE JERK"

** He lives in Sydney - same as me.

** The do actually - f*****ad. ** That is complete bollocks.

** The problem is not with the frequency of the AC supply. ** The supply grid has absolutely precise time keeping over the long term.

The PROBLEM is that any given premises may suffer losses of power for short periods from time to time - over a year these all add up of course. And they all add in the same direction !!!!

Most mains derived clocks react to a power outage by going into a mode where the display blinks and the time resets to midnight or some such. OTHERS ( with battery back up) however revert to an internal oscillator that is only based on a cheap R and C and give no warning that there has been an outage.

The most common outages in homes are due to ELCBs and breakers tripping.

.... Phil

Are you talking about analog TV or digital TV? With analog, it was at the discretion of the station. With digital, it's inscribed into the ATSC (US) and DVB-T (everyone else) standards. Unfortunately, I don't know enough about either of these to explain how to get to these time codes.

In the US, the local PBS station (KTEH) went the other way. They claim to be sending time code signals, but none of my 3 assorted VCR boxes would find it.

Nope. I have a Philips HDRW720. It can use a PBS station for real time setting. See the owners manual at:

on page 22 under "automatic time setting". The problem is that there has been no firmware update to deal with the 2007 change in daylight savings time.

My Tivo 2 can also use a PBS station for date and time, when connected to an antenna.

Most digital DVR's are now integrated with either a cable TV modem or a satellite receiver. Time sync comes from the network. My DirecTV R16-300 DVR is about 3 seconds early, for no obvious reason, which makes time shifted recordings start 3 seconds early, and chop off 3 seconds from the end. Grrr....

Samsung combined Blue-Ray players and DVR work that way. Buried in the setup is the option to specify an NTP server. I like to use: us.pool.ntp.org

Yep. However, if the functionality is there as in a network connected device, and the computer horsepower is available, then network time is just a matter of adding some code.

It's marginal. Loss of power means loss of clock, with no automatic method of restoring the real time. No thanks.

Perhaps a wind up clock would suffice?

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

r

IF it is set to 50HZ and you are on a 60HZ supply - then it would run faster, not slower.

Open it up and see if there is some sort of trimmer capacitor there near the clock chip, adjust it and see what happens. Might have to fiddle with it over some time to get it right

That has nothing whatever to do with the point I was making.

I find it impossible to believe that /any/ microwave oven would use a crystal or resonator -- which costs money -- when the power frequency is /right there/, and free.

They would use the same crystal as the microprocessor, and run the clock in software.

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You can't fix stupid. You can't even put a Band-Aid? on it, because it's
Teflon coated.

I was talking about analogue. Digital here has only appeared in the last decade or so, and even then, early on, there were no boxes you could actually buy to do that. (funny though, the politicians could get wide screen TVs and set top boxes donated quite easily to them - for "testing purposes" you understand).

It's only the last few years the prices have come down to something that's actually reasonable.

On the analogue side, we had *electronics* here that was compatible with a variety of systems around the world for a LONG time, non of which were compatible with our TV stations.

At least you had TV stations that WERE transmitting codes, we didn't. Not till digital anyway.

Arrg. Don't start me on daylight savings. I'm actively unimpressed unless the device supports USER DEFINABLE dst rules.

TiVo is another thing that failed miserably in Australia. The group in charge of keeping things running in Australia and New Zealand is down to

7 people (from 100+?) and will only keep the current licence holders going till that runs out. Shame really. If it actually worked like it does in the US, it would be quite viable. Except they knobbled a lot of the functionality, and charged more for the privileged.

That's pretty much my attitude. Mains locking is cheaper to implement than crystal locking, and if mains locking was better than crystal then no-one would implement cyrstal locking in the first place. But it IS better, AND you get very viable long term battery backed timekeeping with crystals too. That leaves no reason for mains locked clocks to be implemented at all, outside of "novelty" clocks. Really, is saving two cents really worth it when you're pissing off your customers that much?

I don't do windups. Outside of antiques that is. But an antique isn't a timepiece, it's an example of a combination of the limited technology of the day, doing a job that a two dollar Chinese wrist-strapped device can today.

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None of you exist, my Sysop types all this in.

I was, of course, referring to a separate crystal (he said, retro-conning the issue).

William, I've never seen a microwave where the clock wasn't just software in the MPU and I've scrapped a lot of them over the years. Just one 20 cent crystal, and a MPU that cost less than a dollar in production quantities.

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You can't fix stupid. You can't even put a Band-Aid? on it, because it's
Teflon coated.

It is possible to have a second crystal, as I have seen a custom IC that included an RTC inside have its own separate 3.579mhz crystal in addition to the crystal for the CPU function. Both connected to the same IC on separate pins. In this case though, this second crystal would be just for the RTC function, as the low speed would save power, and also the rest of the chip would likely be shut down also to save power hence no software clock. This was an early 1990s design

As microwaves don't have a RTC in them (that I have seen) and simply reset to 12:00 or whatever after a power failure, there is no need for the more sophisticated system described above.

I agree with Michael A Terrell,

There wouldn't be a separate crystal for the clock in a modern microwave, The "clock" and processor would be incorporated into a single chip, and the timekeeping would be surely a software function. The chip would very likely have a single crystal or resonator.

In my original comment, I suggested looking for a trimmer cap across the crystal and trimming it to fine adjust the clock if the inaccuracy is a real issue for the OP .

You also can check the value of the crystal, there is also a very very remote possibility that there was the wrong value, but very close installed at the factory - something like a 3.562 MHZ instead of a

3.579545 MHZ for example, but without sitting and working out the inaccuracy this would cause, this might not be right and might make too big a difference to be the problem.

It will not hurt the rest of the system to run a tiny fraction faster/ slower.

retro-conning

That IS a RTC. It just has no battery backup to ride through power outages.

It would save a lot more power at 32,786 Hz, which is also standard for the application.

ing

Sorry - I was referring to a RTC as a dedicated clock IC either in or out of a custom IC. battery backed up

I would think that a microwave clock would be done in software though, and not have a dedicated clock section in the custom IC, not that it matters though.

retro-conning

would

I'm cool with this. No worries. =20 Plus there are plenty of uC that could wake up once per second just = enough to keep good time, but a crystal and battery are more parts and cost.

Why not donate the SOB and get a new one for $40 and STFU!