MJ Clock Dissection

[Torq_Shep]

Because I am a weird electronics person I decided to suck the solder out of a 1991 clock and see if I can decode it for (potentially nefarious) uses. 

 

In any case, I have decoded 3 of the digits and the blinking colon and have an idea on the 4th digit. Once I have it fully decoded I will share a table with pinouts. However, I also took pictures of the clock LED and the chip underneath it after desoldering. Figured it might be interesting/helpful to some people. 

[Torq_Shep]

https://pdf1.alldatasheet.com/datasheet-pdf/view/108912/ALLEGRO/SCL5463E.html

 

For the clock module soldered in under the display module

[scaleless]

This is awesome!  I've been thinking about adding some TFT displays in the dead space below the clock and this will complement that nicely.

[Torq_Shep]

As far as I know this is only applicable to 1991 clocks. I would love to get my hands on the whole gamut and pin them all out. 

[eaglescout526]

Quartz ones take up the whole cavity so Renix is a bit out of the question.

[scaleless]

While the displays and housings definitely changed, I wouldn't think the clock chip would have.  Unfortunately I'm not keen on spending the time just to take a look lol.  Early clocks had a full first digit unlike later clocks but I would expect the general layout of the pins would be similar.

 

7 minutes ago, eaglescout526 said:

Quartz ones take up the whole cavity so Renix is a bit out of the question.

 

They take up the whole area, but there is still more than enough depth for an Arduino and a display!

[Torq_Shep]

If anyone wants to send me clocks they don't care about being potentially destroyed I will try and pin out all of the years... 

[eaglescout526]

I’m sending ya a couple. Here’s an 86 one and yes this is the one you and I spoke about being taken apart. 
 

[Minuit]

Some of the Jeep VFD clocks (especially the ones on 86 and up SJs) tend to burn up the large power resistors seen in the bottom center of Eaglescout's pic. This must have been a recognized problem as the '91 clock features a bank of identical resistors in parallel to spread the heat among multiple devices, but you can still see where the board has cooked a little bit from the heat.

 

If I read the datasheet correctly, it should be very easy to convert the '91 clock to 24-hour time if you wanted to by removing pin 4's ground connection.

[Torq_Shep]

Very very easy to convert to 24 hour =P I am almost done with my data sheet for the display but I need to check some stuff when I am back home tomorrow.

[eaglescout526]

6 hours ago, Minuit said:

but you can still see where the board has cooked a little bit from the heat.

 

Heh, actually I might’ve done that myself. I had it rigged to power on one day just because it sat in an XJ for god who knows how long at AMC and I had it all set to go and it wouldn’t display the time. Just a dot. So I went to probing to find the resistor that doesn’t have power. I found it and jumped it for a second and kinda scoured the board a little.  But the VFD is fine. 

[Torq_Shep]

I have made really good progress on this!

I have the pinout for the clock that I am 99% sure is correct. I am going to try and run it probably tomorrow night once I can get a hold of a second power supply (Tungsten tube needs lower voltage). Doing reading on controlling VFDs with arduino so I am hoping I can come up with something that will work as a stand alone. 
 

There are some issues to be aware of for anyone doing this. The first digit can only output 1 or 2. The 3rd digit can only output 0-6 and 8. Colon cannot be split to be a period. So if you are going to use this for AFR readout you may want to do AFR readout in Lambda instead of actual AFR (Which I actually prefer). I will also make a quick writeup on how to change it to 24 hour time by hopefully just extracting/cutting one pin on the clock chip. 

 

I am highly considering seeing if I can find a 7 segment addressable clock display that has the same dimensions and similar look as a secondary option.  

[Torq_Shep]

Okay I verified this with a breadboard earlier. My breadboard is cheap and I was having some floating high voltages screwing with me. What I have determined is that this display is kind of a pain in the *you know*. It could be addressed directly with an arduino (uno/nano) and a shift register or with a ATmega 2560. However, you would almost certainly need to use transistors for all 23 input pins to get voltage above the 5v DO on an arduino. Can it be done? Yes. Will it take up a lot of room and have questionable power requirements? Also yes. 

  

 

1991 Jeep Clock Pinout.xlsx

[Torq_Shep]

I managed to fry something on my clock display when I soldered it back together. However, I did use the damaged clock (don't worry the clock I used was already trash) to take some pictures on switching the clock between 12 and 24 hour times. Again this only specifically applies to 1991 era clocks but it may apply to other years. I will know more when I can desolder some more clocks. 

 

Theoretically... If you want to switch to 24 hour time on a 12 hour clock you should be able to do so without a soldering iron (multimeter recommended). 

 

#1 Locate pin 4 on the clock circuit. The front of the circuit board shows where pin 1 is, you need to locate pin 4. Do not get confused with the VFD pins. The inner 2 rows of solder pins are the clock circuit pins.

 

#2 Above this solder pad you are going to score the circuit board to break the connection. I used a razor blade. 

 

#3 Check to make sure you have no continuity. 

 

 

#4 put the clock back together and it should work in 24 hour time only now. 

 

[Torq_Shep]

Say for some reason you prefer 12 hour time (why?), but you followed these instructions to convert to 24 hour time. Or maybe you are outside the U.S. where you use logical time keeping and you have a 1991 era clock that reads in 24-hr and you want 12 hour (again why?).

 

Make a jumper wire and solder those it to the two pins we broke the connection on already. 

 

 

You could also choose to install a switch on this jumper wire and have a switchable 12/24hr clock. That would be kind of cool I guess. 

[Torq_Shep]

[schardein]

On 7/19/2021 at 9:41 PM, Torq_Shep said:

 

Thanks for posting this.  My mind is programmed to 24 hour time, so this is awesome.

[Big_Mark]

Great nerding guys! I just picked up a 91 clock assembly from "All about Auto" wrecking yard here in Snohomish, and was thinking I could shove a Rasberry PI Zero in that assembly, but I don't know what I'd want it to do. Maybe be an MP3 player? Maybe wire up some kind of display to fill the hole where my radio is supposed to go?

I think for now I'll be happy with splicing in the radio harness to get the clock in and working first.