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#225 - 12/29/00 10:11 AM Slow Electronic Clock?  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
Question asked of me:

We have an electronic clock in a Panasonic microwave that the customer says, runs about 5 minutes slow every 6-12 hours or so. I have the unit in out shop and it kept perfect time with my watch here!!

What to test in the house?? ...cycles??...voltage??...amps??

Thankx for any input!!


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#226 - 12/29/00 12:08 PM Re: Slow Electronic Clock?  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
First thing I would suspect would be frequency, however if it is an electronic clock [LED based instead of Analog - motor driven by a synchronous motor], then it would of course have a local oscillator [crystal] which would be the base for the real time clock. Now the possibilities of voltage sags would be suspect.
Check the power quality over time.

We have a typical LED alarm clock that runs just fine while being powered normally from the 120 VAC, but when there is a power failure and it runs on the battery backup [9 Volt Alkaline], it gains an average of 5 minutes. In other words, if the power drops out for a full minute at 11:59 AM, and returns at 12:00 PM, the clock will show 12:05 PM when power is brought up again.
Kind of the reverse of your situation, but does demonstrate the accuracy of a local oscillator.

Scott.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#227 - 12/29/00 04:40 PM Re: Slow Electronic Clock?  
Bennie R. Palmer  Offline
Member
Joined: Nov 2000
Posts: 72
Milwaukie, OR 97267 USA
I agree with Scott, the instability of the time base circuitry, is the most likely cause. This can vary by quality and tolerances of components. Line garbage can be a factor. Many are quite accurate.
This reminds me of one of my "Sea Stories". On the nuclear test site, in the Pacific, we used WW radio time standard signal for synchronizing of time, by injecting this signal into our master timer. We were encountering an interference due to receiving two signals at different time intervals. This was traced to the fact we were receiving them from each direction around the world, and they were of different distances, and a resultant time. We designed a circuit to exclude one signal, and only amplify the other. Talk about accuracy, I prefer my Mickey Mouse Watch.
I understand the atomic decay, time base clock is the most accurate at this time


#228 - 12/29/00 07:11 PM Re: Slow Electronic Clock?  
jeff1  Offline
Junior Member
Joined: Dec 2000
Posts: 2
Hi all,

I have asked the local Utility Company to check the power at this home....the Mrs. also told me about a clock radio that has "words" instead of "numbers"...at first I thought the clock radio had burnt out LED's but the clock radio also worked fine in out shop. The second microwave she tried is also loosing 5-10 minutes a day :-(

Thankx for your time!!

jeff.


#229 - 12/29/00 09:41 PM Re: Slow Electronic Clock?  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
Jeff,

Glad to see that you made it! [Linked Image]
(it was his question)
Make sure to tell us if you find out anything.

Happy New Year!


#230 - 12/30/00 04:06 AM Re: Slow Electronic Clock?  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
What words did the LED clock display? Was it a string of letters, such as H, L, O, S, and the like? Do they randomly appear and are transient [only there for a few seconds], or do they stay resident for a certain time. Does unplugging the clock and repowering it bring up numbers or letters.

Sounds like the place might possibly have a carrier current type system that is interfering with these clocks' display ICs [Integrated Circuits - AKA "Chips"].
Carrier current systems are the controllers that use the AC power branch circuits for the control signals, as well as the power [a different kind of wireless control]. Plug-in Intercoms work this way, along with some lighting control systems sold retail for home use and homeowner installations.
Remember the clocks in School when the time got near the hour, and they would run fast until the minute and second hands were on the 12? These use Carrier Current type of controls.
Another source of trouble could be RFI on the power system, but I have never seen it to that extent.
RFI could be from a variety of sources. Local Radio broadcasts would be the first and most common. These would be either from a commercial AM or FM broadcast output antenna being close to the location [this can be verified visually or by listening for interference on the telephone]. Another Radio source would be a HAM Radio operator, using the band that has the best carrier possibilities for the Radio users, but the worst effects to TV, Telephone and also the local AC power [I do not recall the band, but I think it was 30 MHz "10 meter band"]. My old neighbor was a HAM user and I had to filter the heck out of things to keep the "gremlins" out!!

Other interference sources could be a PC with a power supply that is ready to fry, Inductive components with a ridiculously bad quality issue [harmonics and such], even an alarm system that is wireless.

If the local power company does not find any quality issues on their end, see if you can locate anything suspectable. If you have an oscilloscope, see what the AC wave looks like at different locations and times in the house. Run the problematic devices with the scope connected also to see how it's looking. I would look for transient waves past the 9th harmonic, plus the way the fundamental is distorted [see if it is too sharp at the peaks and stuff!!]. Any abnormal harmonic could be suspect if it gets into the timer crystal [or 555 timer IC].

If you have access to a graphing voltage meter, run it for a day or so to see what the transients look like [transient voltages and currents].

I have posed this problem to a few of my Engineering buddies, but we all have the same thoughts. I'll need to get in contact with a few Electronics Tech friends of mine to see what they think, however they are away for the holidays.

I have got to find out what is happening here! If I ever run across this again, it might be helpful [Linked Image]

The end result is most likely going to be filters, unless the utility company finds un-normally low voltage or brownout problems in their equipment and decide to correct it.

Find out what else [if any] is malfunctioning at this house, such as Incandescent lamps being very dim, or very bright, along with them "singing" [dimmers or AM Radio interferences]. Check for anything that is abnormal, plus check the things that the neighbors are doing, such as home work shops, arc welders, Radio, etc. and see if this might contribute to the problems.

Sorry to give you so much information, but I really have no clue what to do other than a step - by - step approach to see what is going on [kind of stumble across the culprit]. I would like to know what the end result is! and if I was anywhere close.

Keep us informed.

Scott.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!


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