Slow Microwave Clock

[jeff_wisnia]

A few months ago I bought a new Westinghouse WST3501 microwave oven for our office "eating area".

The oven itself works fine, but we're annoyed by the time of day clock losing a couple of minutes a day and having to be reset to the correct time every few days.

I've never seen this happen on several other microwave ovens I've had in the office or at home, it's like the clock in this one isn't synchronized to the 60 Hz line. Other line voltage operated clocks in our office keep the correct time, unless there's a power failure and they don't have a battery backup in them.

I'm guessing that the electronics in this "made in China" oven were designed to run on 50 or 60 Hz power, with just a different power transformer installed in 230 volt models. And, the clock is timed from a poorly tuned and/or temperature sensitive crystal oscillator, not the line frequency.

I e-mailed Westinghouse about this but they put me off to "Fox International" who thusfar hasn't answered my e-mail about it.

Not an earth shaking problem by any means, but my curious mind wants to know what's really going on with the clock function in that oven.

I'd just as soon put a pice of tape over the readout and fughedit, but I can't do that because it's needed for the cooking functions too..

Jeff

[The Daring Dufas]

There could be a jumper on the control board to set 50 or 60 cycle power as a time base. I've seen new equipment arrive with the wrong country power plug installed. Products manufactured for the Southern Hemisphere need electrons that spin in the opposite direction to work properly. You may be able to obtain an electron spin converter if that's the problem.

TDD

[jeff_wisnia]

I actually thought about a jumper, but if there is one and it's set for

50 Hz operation that damn clock would gain 12 minutes PER HOUR, which thank G_d it isn't.

Re the spin converter, is it based on something like this?

Jeff

[HeyBub]

Take it back where you got it and bitch like the third monkey on Noah's gangplank.

[Peter]

[SNIP]

Could be, but unlikely. The typical mass produced (and cheapest) plug-in timers use circuits that count line frequency.

If a timing circuit designed to keep time with a 50 Hz AC supply was connected to 60 Hz AC, I would expect the clock to run fast, not slow. So the slow clock is not likely to be related to a wrongly placed jumper or the use of a circuit designed for a 50 Hz supply.

I've had a chronic problem of the opposite kind in my house. Most but not all of my digital clocks run a few seconds/day fast. I see this with 1 of my 3 clock radios, both VCRs, my DVR, and the clock I've had on every microwave (3 of them in about 20 years). There seems to be no pattern to which home circuit the devices are connected to (happens to devices connected to either 120V arm of my 240V service). Some of the devices are 15+ years old, some are much more recent. Some are dual voltage, some are 120V 60 Hz only. I convinced my electric power company to come out and run diagnostics. They found absolutely nominal readings with no evidence of voltage spikes, frequency deviations, RFI or EMI. The engineer said he had been doing diagnostic work for the same company for more than 10 years and no other customer has ever had a similar complaint. I've resigned myself to making it a routine to reset the time on all of these inaccurate devices at the beginning of each month.

I hope the problem is restricted to my clocks. I'd hate to think that something in this environment is also causing my biologic clock to run fast and causing a shortened life expectancy :-) .

Give me back the old fashioned mechanical hysteresis motors! They never ran fast or slow. They kept my old tube clock radios running accurately for decades. I've got only one motor driven clock left, the one built into my wall oven. Except for my "atomic" desk clock and "atomic" wrist watch, that oven clock keeps the most accurate time in our house.

[Jules Richardson]

OK, I think that's just become my favourite saying for the week :-)

[Jules Richardson]

that'd drift by a factor of 5/6, though.

Interesting fault. I wondered if the clock was on its own oscillator and is supposed to do a periodic resync against the line frequency (once a day, say), with the "resync" part busted on yours - but I'm not sure that makes sense either, because surely the clock would see 0 line pulses all the time and reset itself to some default time each resync (unless the on- board smarts say something like "there's obviously a fault with the pulse- counter, I'll ignore it").

Bad parts, maybe. Perhaps someone goofed and a batch got made with the wrong frequency crystal oscillator. Not sure if the manufacturer would ever own up to that, though.

cheers

Jules

[hrhofmann]

I'd hate to see what she will look like when she is 70 or 80 years old, she'll need a wheelbarrow.

[jeff_wisnia]

I really don't have the nerve to do that because I think I bought it (in a sealed carton) for $29.95 on sale at a Rite Aid pharmacy.

Jeff

[jeff_wisnia]

Maybe she'll look something like the "older" pix here?

Jeff

[The Daring Dufas]

Some IC's have a built in clock that requires an external capacitor to function. There is a probability of less than accurate cap values being the culprit. Another thing that someone else posted on about problems with his clocks and having tests done looking for interference coming from the AC power. I know that transformers for office buildings had to be redesigned after problems were discovered when the age of the personal computer came along. All the switching power supplies were causing overheating due to the asymmetrical loads put on the transformers. I came across a simple power supply circuit that puts out a clock signal from the 60Hz power. I understand that this design used as a time base for a clock is susceptible to line noise.

The cheapness of many consumer electronics items today leads me to believe that best practices are not being used in the design of the circuitry. In an office environment there have got to be all kinds of harmonics flooding the AC power system. If any of you guys are like me, you notice things are off and not quite right with things and can't stand it. I'll be out on a service call somewhere and notice a loose screw on the door handle and I pull a screwdriver out of my pocket to tighten up the errant screw. I once notified a business owner that the toilet in the men's room was leaking and he should call a plumber to fix it, he didn't think it was important until he got a thousand dollar water bill. I like things to work right and find conquering misbehaving systems to be a fun challenge. Now if I could only figure out a way to repair women. 8-)

TDD

[Charlie]

Back around 1967 I was working at a job where we had equipment that was using the power line for timing some process. The question was raised of the accuracy of the line frequency. I got in touch with a guy in Boston Edison' engineering office. At that time IIRC the tolerance on the frequency was 1/10 of a cycle. He pointed out that the root cause of the great Northeast blackout of 1964 was caused not by a short circuit somewhere but by some undue surges on the grid so that various generators got out of sync. That precipitated the generators going off line to protect themselves. You readers who have ever had a rotating machinery lab and tried to merge two generators together will recall the caveats of throwing the switch before the two units were in sync.

As another tidbit of our conversation was that the generating facility ran a standard electric clock of their lines. At about midnight the task was to slowly bring the clock to agree with the WWV time signal. The customer was thus assured that they got all the cycles they were paying for. There fore the best time to set your clock was about 3 am.

I am sure a lot has changed since then what with cesium clocks etc.

Somehow those days were more fun.

Charlie

[WW]

Jeff... Take it home and see if works correct there . That would show if interference at office is the cause. WW

[Nate Nagel]

Used to have a Mr. Coffee coffeemaker w/ "analog" LCD clock. At least twice a week it would just lock up and i'd have to "reboot" the coffeemaker. Never happened once after I installed a TVSS at my panel. I can only ASSume that the quality of the power was not so great.

nate

[HeyBub]

Oh. Here's some more you might find useful:

You're circling the drain, They gonna be drawin' you in chalk on the sidewalk, Gave me the stink-eye He needs flashlight therapy 'Roided up primate Hold a grudge longer than my ex-wife The medicine man's gonna be wavin' chicken claws over your ashes

And, when referring to a suspect, the following have been found to be appropriate: Goblin, Gremlin, Squint, Slope, Miscreant, Do-bad, Slop-sucker, Solid waste, and Chicken-plucker.

When you exhaust this set, just let me know. I've got a million of 'em.

[HeyBub]

Oooh! Good idea!

[HeyBub]

[Bill Gill]

Ok, now's the time for my sister's clock story. Back in the 70s she was working as a DJ at radio station in McAlester, Oklahoma. When they had the big power black out in the North East their electric clock lost several minutes of time. So they reset it. Then for a couple of weeks they had to reset it every day, because it gained time, as the power companies corrected the power line frequency to bring it back into sync with the WWV time. The power line frequency is very stable over long periods. As somebody said up thread the old fashioned electric clock was extremely accurate over years. The power line frequency over short periods is not particularly good, but over the long run it is about as stable as you can get.

Bill

[Peter]

If you don't break them, they don't need to be repaired. The key to successful relationships with women who are important to you is to let them have their way - or if you are really skillful, convincing them that they are having their way even if you know better (also known as child psychology).

[Jon Danniken]

My EYES! They are BURNING!

ARGHHHH!

Jon