The adj knob is pressed on to the metal shaft in your photo. This can be disassembled, but is very difficult. The 240 knob is different from the 280, but is still  pressed on. 

 

 R

Thanks for the post, I'm trying to get a spare clock working now. My 1978 quartz clock started losing time last summer. I had a spare, so took it apart to see what could be changed. There are only 5 components on the circuit board as follows:

1. 16v 100uF capacitor (Nippon chemi con CEO4W)

2. 200 ohm resistor. (Cant figure out the exact specs. It has 200 ohms and either I or 1 JL6 printed on it and its green. Its about 11 or 12 mm long, which from read I have read may mean its a 1 watt??? and 3 or 4 mm wide. Under it on the board is printed R for resistor presumably.) Not sure what kind of resisitor it is. 

3. Next to that is what I'm guessing is a Zener Diode as it has ZD printed on the board next to it, and has a band on one end. Its white with a red band and has either LX or X7 written on it.

4. I think a crystal oscillator labelled 4194.5 TOYO COM 7C4. It has XTA printed on the board next to it.

5. A 16 pin chip that I think the symbol on it may be hitachi? HD44001 7K 33.

 

The capacitors are all over Amazon, so not a problem to find. Does anyone know if any of these other parts can be sourced anywhere? I would like to replace with new as much as possible while I have it apart. Thanks.

Your analysis of the parts is correct...

Resistor, zener, capacitor - Those three parts are used for power supply and regulation*. They are relatively easy to source, and other than the zener voltage, the specs are relatively unimportant. By that, I mean... You could use a 180 Ohm resistor or a 150uF cap. Within reason, the values don't matter. The resistor will dissipate less than half a watt, so a one watt resistor would be fine. Composition (wirewound, metal film, carbon... Doesn't matter.)

Crystal, and control chip - Those two are not easy to source. Hope that your problem is not one of those two.

The HD44001 control chip does not appear to be available. Probably designed for the application and sold only to the clock manufacturer.

And I would try hard to not mess with the crystal. The frequency is a little unusual, and even if you can find another crystal with "close enough" frequency, it's not guaranteed that it would work paired with the electronics inside the control chip.

• They are used as a shunt regulator system with the cap as a filter. System has about 30 mA quiescent current and therefor a little less than that in compliance.

Sorry for geeking out. I was on a roll. 😄

@Captain Obvious Very impressive analysis of the circuit. Thank the Lord I went to school for that!,

I'm fairly certain the problem is either the crystal or the HD44001. I have voltage everywhere, get about a 4 volt drop across the resistor, and the little gear still doesn't spin. This was my spare clock I had pulled out of a junkyard years ago. The one in my car sometimes holds time, sometimes loses lots of time, depending on how it feels. I was hoping to try to see if these were possible to rebuild, and then just swap the clocks and do the same to the other after. I think its a metal resistor, but not 100% certain on that.

https://www.worldwayelec.com/pro/cs-elec/hd44001/4250271

https://www.1sourcecomponents.com/availability/HITACHI--HD44001.htm

https://fr.excesschip.com/product/details/hd44001

https://de.excesschip.com/product/details/hd44001

These are the only things I was able to find online for the 44001. Not affiliated with any of these, so click on them at your own risk. The top place shows they have some with a minimum order of 100, but not sure how accurate that is. I couldnt find a datasheet on these, so not sure if they would need to be programmed or not.