digital clock gains time

[Sureitsoff?]

Hi all. I have an audio timer, which is basically a digital clock that has a relay switched output, that I use as an alarm clock. when the set time arrives it drives a relay and the mains voltage is switched on on sockets on the rear, which powes a hi fi system and a light.. ok simple BUT this clock has statrted to gain up to 20 mins a day so is getting to be useless. does anybody know why this clock should gain quite so much time in one day?

 

[Lucid]

That's a lot for a day. That must be frustrating.

Digital clocks can be sensitive to mains noise which then disrupts the time. I'm guessing that whatever electronic filtering the timer has to try to combat this has probably given up the ghost. Bad caps, perhaps?

 

[Sureitsoff?]

thanks lucid, i shall have a look at the inside and see if any caps look iffy. i did wonder if a ferrite ring might help. (amongst all the assorted mains leads i have amassed over the years can i find one with a ring..............)

 

[johnny2007]

Buy a non chinese clock.

 

[Sureitsoff?]

its actually a japanese Technics unit

 

[SFK]

Used to have one of those and liked it a lot (no idea where it went).

Sorry to say that I think it will be the Resistor Capacitor circuit failing and changing teh timing on the (i bet) 555 chip used for the timing.
Yes have a look at the caps.

But might be hard to identify which is issue and if others will fail.
Suggest you look at the caps that are near a chip numbered 555.

Otherwise Might have to buy a new one:
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=audio+timer&_sacat=0

SFK

 

[Sureitsoff?]

i cant see a chip numbered 555. there is not a lot in there

there are a few on the bay but if i can just swap a couple of caps it will be nice.

ps there is one from japan https://www.ebay.co.uk/itm/Technics...963384?hash=item2f48b019b8:g:-6oAAOSw1NJfN220
but not at that price!

i have used these timers as alarm clocks for years as it is handy to be able to switch a lamp on at the same time as the radio (handy when I used to get up at 3am to go to work!)

 

[SFK]

mn6076 is a timer IC

The caps look okay, but that is what I would change anyway. Can you see cap values, in that includes the brown one marked C2?

If I get time will have a the cucuit.

 

[SFK]

Seems the 6079 counts the 50Hz mains frequently (which I did not know) rather than an RC ballanced oscillating crystal.

Have a read of this. I do not think it will work (perhaps I am biased in that for me it is normally capacitors) but it might be work a try to move the switch and power down.
https://audiokarma.org/forums/index.php?threads/dt-500-running-fast.123676/

Sfk

 

[Sureitsoff?]

thanks for your thoughts SFK i havent got any caps (but I know who has....) he doesnt know it yet but I shall raid his stock! cant see the writing on the c2 one but will have a look in daylight

 

[Harry Bloomfield]

Clocks are either timed by a crystal oscillator running at 32,767Hz, or use the 50Hz mains frequency as the reference. The prior will slightly drift over time, a matter of seconds per month and need correcting. The latter will gain and loose a few seconds per day, but will always be approximately correct year in, year out - unless there is a power cut.

 

[Sureitsoff?]

mn6076 is a timer IC

The caps look okay, but that is what I would change anyway. Can you see cap values, in that includes the brown one marked C2?

If I get time will have a the cucuit.

Hi sfk
the brown caps are marked as follows C2 103Z and under lined 23 C1 103Z underlined 23 C5 1023underlined 23 and the circular blue one C6 is 103P underlined H3 10

if that means anything to you?

Ps my mate only had replacement electrlytics "in stock" so I will replace both of them to start with. Also sods law prevails and it isnt gaining time whilst sat with the case open!

 

[SFK]

the brown caps are marked as follows:
C2 is 103Z underlined 23
C1 is 103Z underlined 23
C5 is 1023 underlined 23
C6 circular blue one is 103P underlined H3 10

The last number represents the number of zeroes.
All values are in picofarads.
For example: 103 becomes 10 + 000 (3 zeroes) pF = 10000 pF = 10 nF.
For example: 224 becomes 22 + 0000 (4 zeroes) pF = 220000 pF = 220 nF = .22 uF.
http://www.kiloohm.info/3-digit-capacitor/1023

So
C2 is 103Z underlined 23 =>> 103 I presume is a 10nF Ceramic Capacitor Brown
C1 is 103Z underlined 23 =>> 103 I presume is a 10nF Ceramic Capacitor Brown
C5 is 1023 underlined 23 =>> 102 I presume is a 1nF Ceramic Capacitor Brown

Next one worries me a bit as I do not know what it looks like, and I admit I cannot remember what the blue colour signifies (multi layer/ higher voltage / higher tolerance).
So following is based on my assumption that it is shaped like the brown ones above, but is simply colored blue:
C6 circular blue one is 103P underlined H3 10 =>> 103 I presume is a 10nF Ceramic Capacitor Blue

Bold text is what to seach for on ebay etc.
SFK

 

[Sureitsoff?]

thanks for that sfk what voltage spec should i look for as some say 50v

 

[SFK]

I would be looking for 50V.