Digital clock is stopping - V70 P1 2000

[Chili58]

V70 P1 year 2000: Issue is that the time clock on instrument panel is slow and stops every now and then. I swapped temporarily the instrument cluster and clock is OK with that. So the issue is in cluster. Soldering did not help; may we did not find the correct place, or the "clock component is broken".

Does anyone know, where to find on circuit board the "clock component" - to get is reviewed in details/better?

[xanthefin]

Crystal oscillators usually generating clock signal. There is some different shapes and forms but will give hint mostly if this is an issue. If you keep meter open try use finger on the clock oscillator if it starts working.

[Chili58]

Where can I find the oscillator here? The photos are on my google cloud: Screw driver on first photo shows two plugs where the multiscreen is connected.

https://drive.google.com/drive/folders/ ... kPI7rlg?us

p=sharing

[aeg]

There are two crystals and one ceramic resonator on that board. The one for the clock is almost certainly XTL2, the 32768Hz one in MA406 package near the pushbutton. Put a scope on pin 7 of the 74HC7292 and compare the good vs bad clusters.

[Chili58]

There are two crystals and one ceramic resonator on that board. The one for the clock is almost certainly XTL2, the 32768Hz one in MA406 package near the pushbutton. Put a scope on pin 7 of the 74HC7292 and compare the good vs bad clusters.

Thanks a lot! I have a good one and bad board available; can I compare those and do I need an oscilloscope for that to see, if there are differences? I do not have that one, but can purchase a one just for fun. The bad clock is now stopped.

Pin 7 - is it on the photo hereby at lower right corner area - the last pin?

Is it so, that the crystal is most probably broken and needs to be replaced? Or could it be bad soldering?
The clock was slowing down and every now and then stopped - and looks to be stopped now permanently.

[aeg]

See here for pin numbers:

TC74HC7292AF pinout.gif (8.38 KiB) Viewed 236 times

On a stopped clock, you could measure with a voltmeter. I would expect to see a constant voltage 0V, 3.3V or 5V on pin 7 and the same on pin 4. On a working clock, pin 7 would have a rapidly changing voltage. Pin 4 would probably measure as 1.6V or 2.5V on DC volts and 3.5V or 2.3V on AC volts. You could also check pin 16, it should be a steady voltage, probably 3.3V or 5V. If not, there is a power supply problem. All measurements are relative to ground. You can use pin 8 for the ground lead, or one of the two ground plane vias (holes) near the letter "L" in "XTL2", or the lead on the pushbutton with the "+" trace pattern.

A slow clock will look identical to a working clock on a voltmeter. With a digital oscilloscope, you can measure the frequency. So a working clock would be 2Hz or about 500ms full cycle on pin 7, and about 32768Hz on pin 4. The error should be less than 0.1%. A slow clock would have much higher error.

An entry level Chinese portable oscilloscope such as Owon HDS242 or Zeeweii DSO2512G would cost about USD$150. Actually, a "junk" oscilloscope such as JYE Tech DSO150 (about USD$30) would be good enough for this purpose also.

My first guess would be the crystal is bad. It could also be one of the chips, or one of the load capacitors C38 or C39. It could also be conductive residue on the PCB, you could try cleaning the PCB area with isopropyl alcohol on a Q-tip. Or it could be some other strange and wonderful problem. I don't think it's bad soldering, but you could try resoldering. Be careful not to touch the capacitors (pink or brown components) with the soldering iron, this can make them crack internally, so they should only be soldered with hot air.

[Chili58]

Wow! I'll do that volt measurement work today!

[Chili58]

There are two old, but pretty much not used oscilloscopes for sale - price is negotiable, but each is some 30 eur. What is your opinion about these; suitable for car instruments, or not?

[aeg]

Those are analog oscilloscopes, so the time base accuracy is only about 3%. The clock could be slow by 1 hour per day, and you wouldn't see it. Also, they are 30+ years old, so they could be broken. Then you would need another oscilloscope to repair them. So I wouldn't recommend those scopes for this task. It might make sense to buy one if you think it would be fun to experiment with.

Another option to measure the frequency is a laptop and a Saleae clone.

If the bad clock is totally stopped, then the voltmeter measurement will at least confirm that we're looking at the right circuit.

[Chili58]

Finally I did not managed to get results and ended up to purchase a used instrument package ftom a very similar donator - and its working.