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  #76  
Old October 17th, 2017, 11:51
Swecherokee Swecherokee is offline
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Re: Overhead Console Computer

HI! Know it's a old thread.
The pictures in the thread is gone.
This reset thing, where do I find that on the pcb?
I have tried change all caps, and the two voltage regulators and the christall.
Still dead, the L487 gets very hot.

(sorry bad English, I'm from Sweden)
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  #77  
Old October 17th, 2017, 20:14
90xj06's Avatar
90xj06 90xj06 is offline
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Re: Overhead Console Computer

I'm winging this from memory. But I think the country reset is pin 5 and goes to (pin 3 or pin 4) on the 5 pin regulator. Did yours have the blue 3 pin crystal or the silver metal one? I will try and find a spare one to look at tomorrow.
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  #78  
Old October 18th, 2017, 09:35
Swecherokee Swecherokee is offline
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Re: Overhead Console Computer

My have the blue 3 pin crystal.
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  #79  
Old October 21st, 2017, 13:46
tjmotter tjmotter is offline
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Re: Overhead Console Computer

Quote:
Originally Posted by Swecherokee View Post
HI! Know it's a old thread.
The pictures in the thread is gone.
This reset thing, where do I find that on the pcb?
I have tried change all caps, and the two voltage regulators and the christall.
Still dead, the L487 gets very hot.

(sorry bad English, I'm from Sweden)
I stopped using the L487 because it gets too hot. Instead, I now use an L4947 (Jeep moved to this part on the late model ZJ's) which gets warm to the touch but doesn't generate any where near the heat of the L487. They are available on eBay for about $3.00.

Sorry about the picture removal. Photobucket decided that I needed to pay them if I wanted to keep using their service and I decided that I didn't want to pay them so I had to remove the pictures.

The 3 pin crystal has an integrated capacitor that fails. I find it easier to solder in a standard 2 pin (4MHz) crystal and then add a 47pF capacitor between one of the leads on the backside (I use the one closest to the middle of the board) and the center hole (now unused - which ties to ground).

Not sure what the "reset" discussion is about. I have fixed a dozen of these things and haven't seen that. These regulators do have a "reset" function build into them but it is all hardwired and is triggered by a capacitor and a signal from the CPU. This function is only used by the CPU and there isn't any way to mess with it (other than soldering a wire between pin 5 and pin 2 which essentially bi-passes it). If after power on you have 4.5V-5V on pin 2, the reset function is working properly (if it is 0, you have a problem and may need to solder a 100nF capacitor between pin 4 and ground - this capacitor is what triggers the reset). Also, make sure that you have a good connection between pin 5 of the regulator and the middle 100uF capacitor (just above the crystal). This capacitor stabilizes the 5V signal and without a good connection, the reset function won't work (and you will see 0 volts on pin 2).

Note that the left most button on the console will turn the unit off so after applying power to the board, always press that button first to see if it comes on.

If you are still having problems, send me a PM with your email and I will send you the pictures.

HTH
Todd

Last edited by tjmotter; October 21st, 2017 at 14:16.
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  #80  
Old October 21st, 2017, 14:14
tjmotter tjmotter is offline
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Re: Overhead Console Computer

Quote:
Originally Posted by 90xj06 View Post
so im back to working on my compass. i replaced all the caps and removed the little ceramic ones. all the traces are good but it wont turn on on its own. i have to ground the reset pin and then it will turn on. im not sure where to look now.
You will find the datasheet for the L4947 at this link: http://www.mouser.com/ds/2/389/stmic...074-329631.pdf

It is the same function as the L487 you have now but runs MUCH cooler!

What the datasheet describes is that the "reset" function supervises the output (on pin 5) and then charges up a 100nF capacitor (one of the tiny surface mount ones on the board) on pin 4 (to ground) to create a small delay. Once the cap is charged (microseconds), you should have 4.5V-5V of power on pin 2 of the regulator. If this isn't happening, you need to check two things:

1) the 100uF capacitor (sits in the middle of the three 100uF capacitors) is directly wired to pin 5. If not, the voltage on the regulator won't stabilize and pin 2 will never get energized. BTW, it goes without saying that you need to make sure that the capacitor is still good and that the negative side still connects to ground (the ground connection is one of the traces that frys so you need to double check it)

2) there is a small surface mount 100nF (0.1uF) capacitor that sits between pin 4 and ground. This can sometimes fry due to heat and if so, the pin will never charge and the board will never light. If you have a good meter that can check capacitance, you can try to check it but they are VERY cheap ($3.00 will buy you 100 of them) so I usually just change them out or (if the board is burned in this area), I switch to a ceramic "through-hole" capacitor and solder it on the backside of the board between pin 4 and ground.

Same offer as my earlier post - if you are still having trouble, send me a PM with your email address and I will send you some pics and further guidance.

Also note, as per my earlier post, you can "kinda" work around this by soldering a wire between pin 5 (5V out) and Pin 2 (reset out) on the regulator but I don't recommend this because it makes it impossible for the CPU to reset itself if it gets confused. Having said this, it has the effect of removing the reset function from the equation and the board should start up. I often do this when I start working on a board just to figure out what I am dealing with but I always complete the repair properly to avoid other issues.

HTH
Todd

Last edited by tjmotter; October 21st, 2017 at 14:40.
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  #81  
Old October 22nd, 2017, 12:29
Swecherokee Swecherokee is offline
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Re: Overhead Console Computer

Thanks for good answer!
Quote:
Originally Posted by tjmotter View Post
The 3 pin crystal has an integrated capacitor that fails. I find it easier to solder in a standard 2 pin (4MHz) crystal and then add a 47pF capacitor between one of the leads on the backside (I use the one closest to the middle of the board) and the center hole (now unused - which ties to ground).

HTH
Todd
What does this 47pF capacitor do? If I don't use this and use a standard 2pin crystal. Would the display stay dead then?

I did put a 4MHz 2 pin crystal there. So maybe if I add that 47pF it would light up?
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  #82  
Old October 22nd, 2017, 13:00
tjmotter tjmotter is offline
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Re: Overhead Console Computer

Quote:
Originally Posted by Swecherokee View Post
Thanks for good answer!

What does this 47pF capacitor do? If I don't use this and use a standard 2pin crystal. Would the display stay dead then?

I did put a 4MHz 2 pin crystal there. So maybe if I add that 47pF it would light up?
Yes, you need the 47pF capacitor off one lead of the 2 pin crystal or the board won't light up. I ran into this with a board that came with the 3 pin design from the factory. I couldn't get the board to work after changing the crystal to a 2 pin version (the 3 pin versions are no longer available) so I used an oscilloscope to check the output. When I compared it to an older board that came from the factory with a 2 pin crystal I noted that they had a capacitor installed and when I checked both boards with the oscilloscope I found that the amplitude was lower on the version with the capacitor so I installed the the 47pF capacitor and the board worked perfectly. When I re-checked with the oscilloscope, it was the same as the original board.

I don't know if it will make a difference but I always connect the capacitor to the pin on the crystal that is closest to the center of the board because that is how it was configured on the board that came this way.

HTH
Todd

Last edited by tjmotter; October 22nd, 2017 at 13:03.
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  #83  
Old October 24th, 2017, 01:17
Swecherokee Swecherokee is offline
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Re: Overhead Console Computer

Put in a 47pf but no difference. Need to look more on it.
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