I built this circuit (clock with alarm and timer). Everything seems to work well except that it runs fast, very fast...several hours in just 1 day. At first I rechecked all components and they seemed good, checking every diode as they seem to blow easily if not heatsinked well. All was well. Then after reading the
Datasheet for the LM8560 I thought I had found the problem... did I have J1 (Jumper 1) connected for 50Hz operation and not 60Hz operation. Nope! This was ok too! Now I am stumped as to why it runs so fast.

Anyone have any ideas/suggestions?

Schematic:
www.bakpakr.com/downloads/clock.jpg

Datasheet:
www.bakpakr.com/downloads/LM8560.pdf


Thanks

 

Well, that seems to be a bit of a clue, there.

Sounds like major wiring problems to me.

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What frequency is the mains where you live?

Is it stable?

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Alvol:

The pcb was preprinted... a kit! The wiring is fine and after checking I believe the components are as well.

Hero999:

I'm in the US, the freq. is 60Hz, which is the default with no pin connection.

 

Question; How fast 4 hours 48 minutes? Always the same?

I made something like this in the 1970s. My problem was the clock was fine all night but ran fast in the daytime. I found every time the elevator motors turned on I got an extra count. (noisy power line) Check R2C4. The capacitor might be smaller than you think. You could make C4 larger to filter out noise.

 

Did you clean the board? Solder flux may be causing erratic operation.

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i believe I did check solder connections and cleaned the board. What is a good substance to clean the board with...

 

You could use an external crystal oscillator for the clock.

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You may have a bad clock IC, I saw one do this once however it was not an LM8560.

 

Why does every school kid need to make a clock?
In "the good old days", clock chips were sold and everybody made a clock. Now, clock chips are available only if you buy thousands of them. Millions (hundreds?) of counters and gates chips are needed to make a clock without a "clock" IC.

I bought some clock radios on sale for only $.99 CAN. The clocks work OK but the radios are crap. It probably cost more than I paid to ship them from China to me.

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You can clean the solder flux off with 99% isopropyl alcohol.
Which diodes are getting hot? None of them should be.

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The clock has provision for a back-up battery to keep it going when mains power has failed.
To keep time during mains failure it has an internal oscillator which I guess has its frequency determined by C3/R3.

So, if the 50/60 hz input to pin 25 is faulty in some way, it could be running on the RC oscillator, which could be (and probably is) way off frequency.

I have a clock which does just this, if the mains fails, the clock runs fast.

JimB

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For the learning experience, I suppose. No better way to gain a knowledge of gates and counters than to build a functional clock.

Actually, it only takes about 7 chips to make one.

www.circuitdb.com/show.php?cid=99

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That was my question back in the first reply. Diodes seldom need a heat sink (and if they did, where would you buy one?)

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They are usually just copper 'tabs' bent round the thick wires of the rectifier and soldered - with the tabs sticking up in free air.

However, it's pretty rare these days - and certainly no need for anything like that in a clock?.

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