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The clock in our 2000 XK8 is losing time quite noticeably. Perhaps as much as 5 minutes per hour. Scouring the forum for answers gave no Joy. This thread was informative but... https://www.jaguarforums.com/forum/x...repair-249083/
...But I'm looking for understanding of the failure mode and a real solution. Looking at the electrical diagrams I have does not yield anything useful. Does anyone have a schematic and writeup of the minor instruments functionality?
I'm thinking that if there was a damaged or missing tooth in the gearing the loss of time would be consistent at some period with a variable degree of tooth skipping based on how bad the tooth was damaged. OR if there was a weak drive signal to the stepper causing mis-steps the loss of time would not be constant and effected by outside conditions (voltage, temp, vibration etc). Lastly I discount a bad xtal osc clock being off given that this appears to effect far too many of our cars. But of course as I write I can think of many ways the osc would be off.
So I am looking for a schematic, part numbers and who made the actual clockworks. And anything else that helps me understand what is going on.
Atlastajag1 did a follow up thread to the one you looked at and at post #11 dibbit links to a pdf detailing the internals of the clock module and repair itself.
See https://www.jaguarforums.com/forum/x...repair-251710/
From reading the above referenced pdf in the thread it appears that the stepper motor drive gear failure is the cause of the clock losing time. The proposed solution is to get a more commonly available stepper motor and taking its drive gear and putting it into the failing clocks stepper. The advantage here is that the diameter and length of the hour and minute shafts are retained.
It appears that the clock motor stepper is made by Juken Swiss Technology but I do not see any references to a X16 stepper. They do have what they call an updated clock motor the X10. https://jukenswisstech.com/project/stepper-motors/
I've made a little progress in figuring out a fix to my clock problem. I bought a used 1999 Minor Instrument Pack (MIP) so as to have something to take apart and get part numbers. The clock IC on this MIP is AX1250614PG. I have not been able to locate a datasheet for it yet. The clock stepper motor appears to be 152*12.5. I have an email into Minitools with the photo of the stepper in hopes that they have a replacement they can recommend. We will see how that works out.
I'll be hooking the MIP to 12 volts tomorrow and then will be able to see if the clock on this MIP is working. It looks like FC79-16 is ground and FC79-17 is +12. I'll check that for sanity of course.
If this does power the clock then I would be able to verify if it is keeping time. Based on the "common" fault being a broken tooth on the 6 tooth drive gear a clock with 1 missing tooth would lose 10 minutes per hour. 20 minutes for 2 teeth etc.
The plot thickens... I went to see how much time the clock in the car looses but discovered that it does to run at all with the key off. This is unexpected. When driving the clock does run but looses time. I'm just not sure how much it runs slow and if it does not run with the key off intermittently. Need more observation and testing.
On the other front the minor instrument pack I got from eBay has a clock that does keep accurate time. I am powering this clock on the bench using FC79-16 as ground and FC79-17 as +12.
I assume that FC79-17 is always powered and thus powers the clock. This is also indicated by Figure 08.1 in the 2000 electrical manual. FC79-17 is sourced from the Major Instrument Pack. I'll have to dig around more to see if there is a root cause I can find.
The photo shows how I tested the clock on the bench.
As far as I can see you are correct - the minor instrument pack has a permanent B+ supply on pin 17. The only one that should be switched is the illumination supply on pin 8 (although the wiring diagram shows that also as permanently B+, I think that must be an error).
If I were you I would check the fuses to the main instrument pack just in case.
Thanks for the sanity check. Checking the fuse shows that it is OK.
If I were designing this clock I would have 12 volts to the clock chip always hot and 12 volts to the time adjust hot only when the ignition was on. Likely there would be a blocking diode in there to prevent back feeding.
My clock is only running with the ignition on and as would be expected can only be adjusted with the ignition on.
I am assuming that the clock cannot be adjusted with the ignition on. Would someone please verify this is correct for me (big thanks!)
My next step is to trace out the circuit for the clock to see if I can identify the always on voltage and clock adjust voltage. If someone knows where a schematic for the Minor Instrument Pack is that would be super.
My wiring diagram shows two fuses to the instrument pack - did you check the right one? Also, possibly a stupid question, did you check to see if FC79-17 on the harness has B+ always on?
My car is the sat nav version, so I can't check how the clock adjust buttons work, but as the wiring diagram doesn't show any switched supply to the minor cluster, I would assume those adjust buttons are always supposed to work. Maybe someone else can check.
I have not taken the car apart yet. I am only working on a spare Minor Instrument Pack. So asking if I checked FC79-17 is a great question. The answer being no not yet.
I've drawn a schematic for the clock and see only one 12 volt source to it. Thus I can conclude that the clock is adjustable with the ignition off. Someone will verify sooner or later.
So far I have only limited my "study' to the instruments pack pages. I'll expand to trace out the two 12 volt sources to the Major Instrument Pack and verify that both fuses are on. Also on a side note - the fog lamp switches do not appear to work. I'll be looking to see if there is any circuitry in common.
Just climbed into mine with no key with me. Clock dead accurate and the time adjustment buttons work with no key.
Super thanks for that. Now I need to see where I end up getting only switched power and not battery power to the clock. This appears to be from the Main instrument Module. Darn I really don't want to tear the whole thing apart.
It's very easy to get to the minor instrument pack - the wood dash panel pulls out (pull from the bottom, then when it has popped out, pull down to release the top catches). The instrument pack is held in with four screws. I wouldn't be trying to get to the main instrument cluster at this point.
When the fog light indicators stopped working in my car, it turned out the battery backed alarm sounder had failed and was taking the fuse out. Unplugging the sounder fixed the problem.
We just got back from an hour long drive. The clock ran with the ignition on and looked to be keeping good time but was not running with the ignition off. The speculation was that when we noticed the clock loosing time before I assumed that we had a bad stepper motor. It never occurred to me that the clock would lose power when the ignition was off. And looking at the wiring diagrams It should not happen that way. Of course it is so... Both fuse 18 (battery power) and fuse 13 (ignition switched) to the Major Instrument Pack appear to be OK. It is presumed that these fuses feed the Minor Instrument Pack and thus the clock. At some point I will move the car out to where I can get better access to the fuses to verify that they actually have voltages going to them and continuity of the fuse. Plus I think the Minor Instrument Pack needs to come out to verify that there is battery voltage on FC79-17. My wife is not too keen on the Idea and it is her car.
A side note on the fog lights. I pulled the fog light relay and fuse and once they were back in the fog lights were working alone with the fog light indicator.
If anyone had a photo of the front and back of the Major Instrument Pack PCB I would like to get a look at it. The idea is tr trace the circuitry to see if I can see where the clock is getting power from.
Yet another CLOCK thread (analog)
