I've got a Kenwood AT-70 audio timer in immaculate shape. It looks great, and everything works... except that it runs fast. After about 12 hours it's fast by almost a minute. I replaced all of the electrolytic caps in the unit, but that had no effect. It's set on 60 Hz and 110~120V via the switches on the back.
My plan was to use this as a nice vintage clock, but if it can't keep decent time, it's not really of any use at all :/
Now, I know that the timer gets its time signal from the power line frequency. I also know that my coffee pot probably does the exact same thing. The coffee pot keeps perfect time though. So, I'm guessing something is a little hosed in the timer circuitry. But what? Where would I begin to look?
Charles.
My plan was to use this as a nice vintage clock, but if it can't keep decent time, it's not really of any use at all :/
Now, I know that the timer gets its time signal from the power line frequency. I also know that my coffee pot probably does the exact same thing. The coffee pot keeps perfect time though. So, I'm guessing something is a little hosed in the timer circuitry. But what? Where would I begin to look?
Charles.
the USA might be different, but the UK uses a synchronous clock to check the accuracy of the frequency they output to the grid.
You buy an electric clock and it keeps good time. It runs a little bit slow when the demand pulls the mains frequency below 50Hz and it runs a little bit fast when the demand is low enough that the generators can push the frequency above 50Hz.
Averaged over a year the clock will be spot on. Over a week it's usually within 10seconds, over a day it can be upto +-20seconds out
If you Kenwood clock cannot maintain time averaged over a week, then it almost certainly does not use mains frequency as it's time base.
You buy an electric clock and it keeps good time. It runs a little bit slow when the demand pulls the mains frequency below 50Hz and it runs a little bit fast when the demand is low enough that the generators can push the frequency above 50Hz.
Averaged over a year the clock will be spot on. Over a week it's usually within 10seconds, over a day it can be upto +-20seconds out
If you Kenwood clock cannot maintain time averaged over a week, then it almost certainly does not use mains frequency as it's time base.
I've got a Kenwood AT-80 and that is locked to the mains.
50 to 60 Hz is a 20% increase and so 1 minute out in 24 hours doesn't fit the bill.
Three possibilities... your line frequency is way out which is unlikely if it is from a utility company. Don't discount the idea though. Is the error consistent over each hour of the day ?
Secondly there could be an issue with the internal dividers in the chip... worth looking what it uses because it is probably of the same type as used in many alarm clock/radios.
Thirdly, it isn't locked to the mains but I think that unlikely. Have a look for a crystal next to the big chip.
I found this picture on the web... looks like it uses discrete logic for something... tbh never seen anything like that. There seem to be three 10k's going to the base of the relay driver so I would guess its all some form of logic gating and not directly related to 50/60Hz frequency division.
Look the big chip up and see if you can find a data sheet and what it says re 50/60 Hz operation.
50 to 60 Hz is a 20% increase and so 1 minute out in 24 hours doesn't fit the bill.
Three possibilities... your line frequency is way out which is unlikely if it is from a utility company. Don't discount the idea though. Is the error consistent over each hour of the day ?
Secondly there could be an issue with the internal dividers in the chip... worth looking what it uses because it is probably of the same type as used in many alarm clock/radios.
Thirdly, it isn't locked to the mains but I think that unlikely. Have a look for a crystal next to the big chip.
I found this picture on the web... looks like it uses discrete logic for something... tbh never seen anything like that. There seem to be three 10k's going to the base of the relay driver so I would guess its all some form of logic gating and not directly related to 50/60Hz frequency division.
Look the big chip up and see if you can find a data sheet and what it says re 50/60 Hz operation.
Attachments
1 minute/12 hour = 1/720, this is not compatible even with the present, ~free running US mains, and it's not compatible with a crystal oscillator drift either: if such an oscillator tries to drift more than a few hundreds ppm, it will either stop or switch to a multivibrator mode, which will be many percents or tens of percents high or low.
I see two plausible explanations: it is mains-locked, but your mains is polluted by interferences of some kind, which is completely compatible with it running fast, or it has an optional battery back-up with a built-in RC oscillator substitute for the mains, and for some reason it operates in back-up mode, even if the Kenwood does normally not have this option included.
I see two plausible explanations: it is mains-locked, but your mains is polluted by interferences of some kind, which is completely compatible with it running fast, or it has an optional battery back-up with a built-in RC oscillator substitute for the mains, and for some reason it operates in back-up mode, even if the Kenwood does normally not have this option included.
- Status
- Not open for further replies.