SpeedyZ

Question is will either of these circuits work? This is the first thing on the IPC (Instrument Panel Cluster) that the data buss goes through. I assume it is spike protection. This is what I think the circuit looks like, I'm not 100% since this is a multilayered board. The data buss idles at 0VDC and each device on the buss pulls the buss up around 7.5 VDC to talk. You can see the data on a scope in a post above. So either the IPC can pull up the buss and everything on the right side will see the IPC, or anything on the data buss (right side) can pull the buss up and the IPC will hear it. If you look at the photo second photo in post #10 you can see the components have notches on the bottom, normally diodes are marked on the cathode which make this look like Version A of this diagram. But if this is the cathode to ground is this not going to conduct anytime the buss is pulled high? On the other hand version B looks like it would not ground the buss but it looks like if the IPC pulls the line high it would not pass to the data buss until it was pulled over 7.5V. What is everyone's thoughts? I'm no engineer, I just play one at work.

Bill Dearborn

Are you sure of these layouts? If both components are Zener diodes with a reference voltage of 7.5V the diagrams do not look correct. From one of the datasheets I saw forward conduction is about 1.5V drop across these diodes so on diagram A the diode to ground will limit the signal level to about 1.5V which probably will not work. In diagram B the diode to ground will limit the signal level to 7.5V max but the Zener to the right is not going to conduct at that point since its reference voltage is also 7.5V + what ever voltage drop appears in the circuits it is feeding. In other words the downstream modules on the bus will never see it pull above the general area of 0V. Are the two diodes used in two different circuits?
Bill

NOT-MEE

Is there any of the diodes in the other circuits to help identify it.
I'm looking thru the gm esi database of schematics.
I doesn't go to circuit level on that component.
Have you identified what layer that pad is on?
I can get you connector pin out to help if need be?
It mostly is a block diagram.
Pm pacethis he might have a extra board.
He allways has non hud clusters.

Miles in Michigan

Are you sure the signal on the left is used for transmit and receive? Sometimes for a bus, there are seperate tx and rx lines on the microprocessor, and they are both hooked up to a transceiver (or set of components that function as a transceiver). The Tx is usually hooked up to the Rx with a diode so you can 'hear' yourself, but the diode prevents other people's talking from putting a voltage on your Tx pin. CAN in Freescale chips (HCS12) is wired up that way.

How do you like the Fluke ScopeMeter, BTW?

SpeedyZ

OK, here is the latest. I pulled the other component off the board, the right hand one circled in post #10 above. The bottom of the right hand part is connected to the data buss pin in the connector on the back of the IPC, I can't find the data buss anywhere else on the board so I think it only goes to the bottom of the right component. The top of both components are connected together and connected to the data buss in side the IPC. The bottom of the left component is connected to ground. So they are attached as shown in the diagrams A and B above but they may not be diodes. I was assuming they were zener diodes because of the number found but they may not even be diodes. Both components are shorted. The best I can read with a cheap meter they show less than .1 ohms in either direction. The buss (and these components) was hit with 128VAC. And it appears that these components shorting saved all the other modules on the car! When I started the buss was shorted to ground, removing the left component released the buss from ground and the IPC does work again, but I still need to replace these components. Can anyone identify these components? Both components are marked exactly the same and the markings are:

M 5997
ZP012

The "M" is the Motorola bat wings (big M) logo. There is a notch in the component on the "M" end so it looks to be a polarized device. Nothing else anywhere on the board, caps or diodes looks like these components. I assumed because of the number these were 1N5997 7.5V 500mW Zener diodes because the buss operates just under 7.5VDC. But I don't see how the circuit could work the way they are attached. Either side of the circuit, either the IPC or any other module on the buss must be able to pull up the buss and what ever device on the other side of the buss has to see that data. Again, with both components shorted the entire data buss on the car was shorted to ground and nothing could talk to anything. When the left component was remove that released the buss from ground and the IPC would work fine with the right component still shorted.

SteveDoten

don't have the answer, pm Pacethis for a non hud board if this doesn't work