Re: Improving a slow/fast digital clock
Here's some more pics of the inside of this thing. I took one with a light source behind the board to make the traces more visible like an x-ray. Sadly, nothing too interesting going on in there. I managed to work out what all those pins are for and that the clock is indeed crystal-based.
I popped off the board which holds the buttons and the display to the face plate and I was able to spot the crystal tucked under the corner of the display there. The proprietary epoxy blob chip is directly under the LCD as well, so no need to take that out as well, since it might not line up properly again.
That J pin we saw connects to the base of the S8050 transistor, so it's the control signal for the relay. The PWR pin is a sense wire connected directly to the unregulated rectified DC via a resistor and tells the chip whether or not the thing is actually plugged in, since it won't pull the relay when it's not, even if you manually set it to "ON". VCC and GND are self explanatory: GND is GND and VCC is a zener-regulated supply for the IC AND the battery, so now we know what the battery does too: it's simply placed in parallel with VCC and has a ceramic cap between it and GND. There IS a resistor feeding its + terminal from VCC, but it's got a single black band on it, so it's zero ohms used as a jumper, isn't it ? The relay's VCC comes from the unregulated DC as well.
So that's about it....not much I can do to improve this thing. Funny thing is that it's sat unplugged for a couple of days now and it seems to be running SLOW now - when plugged in, it would run too fast, though I haven't done an in-depth analysis and actually watch the thing carefully, but that's the way it feels...
Here's some more pics of the inside of this thing. I took one with a light source behind the board to make the traces more visible like an x-ray. Sadly, nothing too interesting going on in there. I managed to work out what all those pins are for and that the clock is indeed crystal-based.
I popped off the board which holds the buttons and the display to the face plate and I was able to spot the crystal tucked under the corner of the display there. The proprietary epoxy blob chip is directly under the LCD as well, so no need to take that out as well, since it might not line up properly again.
That J pin we saw connects to the base of the S8050 transistor, so it's the control signal for the relay. The PWR pin is a sense wire connected directly to the unregulated rectified DC via a resistor and tells the chip whether or not the thing is actually plugged in, since it won't pull the relay when it's not, even if you manually set it to "ON". VCC and GND are self explanatory: GND is GND and VCC is a zener-regulated supply for the IC AND the battery, so now we know what the battery does too: it's simply placed in parallel with VCC and has a ceramic cap between it and GND. There IS a resistor feeding its + terminal from VCC, but it's got a single black band on it, so it's zero ohms used as a jumper, isn't it ? The relay's VCC comes from the unregulated DC as well.
So that's about it....not much I can do to improve this thing. Funny thing is that it's sat unplugged for a couple of days now and it seems to be running SLOW now - when plugged in, it would run too fast, though I haven't done an in-depth analysis and actually watch the thing carefully, but that's the way it feels...
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