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.

I see sites like that all the time claiming that they have stock of old obsolete electronics. I've never actually tried to order from any of them, but I'm skeptical as to the legitimacy of them. Might be completely legit, might be a complete scam.

And that's an interesting thought about the programability of the 44001. I guess there is a possibility it's a programmable part. And if so, there's the follow-up question of "when you buy it, is it already programmed?".

18 hours ago, socorob said:

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.

The 4V drop across the resistor is good. It should be "battery voltage - zener voltage" across the resistor. So if battery is 12 and zener is 7.5, you should see 4.5V across the resistor. if you've got that correct drop across the resistor and the clock doesn't run, then it's either mechanical or one of the remaining components (Xtal or control chip).

Your other clock that sometimes holds time and sometimes doesn't sounds more mechanical than electrical. Maybe old lube has turned to tar and is gumming up the works?

I found on another forum where someone posted this in 2014 where they called ToyoCom, which I think is now Epson about the crystal:

Thanks a lot, I gave them a call and they only sell in bulk, $300 minimum order. Wouldn't answer any questions.

https://www.4starelectronics.com/mfgs/Toyo-Distributors.html

This was the website he said he called.

I was hoping there would be a source for some old stock somewhere to rebuild these, because I like having an accurate clock and like the look of the stock clock.

This clock I took apart doesn't appear to ever had lube anywhere, unless it totally evaporated and disappeared, so I'm not sure if these clocks used any lube from the factory. I tried running it with all the gears off except for the 1 drive gear, and that doesn't turn. I don't believe the coil could fail without it being noticeable.

Edited yesterday at 01:56 PM1 day by socorob

Yeah, that thread popped up when I was poking around as well. >> https://www.zcar.com/threads/280z-clock-part.354058/

Yeah, unfortunately, it's sounding like it might be the chip or the crystal. I could probably tell you which of those two items are not working, but it would take an oscilloscope.

The non working clocks capacitor I removed measures 111uF, so that was probably still good.

The working clock that loses time capacitor starts off at 0, then takes a minute or 2 and only climbs to .8uF, then goes up and down from .8 to .6, so maybe the new capacitor will fix this one. I cleaned all the gears, resoldered all the connections and replaced the cap so maybe I'll get lucky. I'll let it run a couple days to see. Yesterday it lost 10 min in 24 hours, a few days before about 6 min in 24 hours, and a few days before that 45 min in 12 hours. In between all this it held perfect time in 24 hour periods. Its very random when it works or doesn't. I looked everywhere trying to find a 12v quartz movement or buy another clock to gut that could be retrofitted into this, but for the cost, it would probably be better just to send it to instrument services, they said they charge $200 to rebuild them.

Have you heard of @zclocks on this site. He’s pretty much the expert on these clocks. I’d reach out to him and see if he will take it on.