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Hi Swany! I took the measurements and results are not what you expected, except one. Results were taken in normal state, nothing pressed, those are in yellow color and when S84 is pressed in red color.

I ordered 2950A CZ 5.0, it should arrive in two days, then I can replace that.
View attachment 2612710
Thanks for the measurements. It looks like the trace going to the Intel microcontroller (P2.7 pin) is low so all the voltage is being dropped across one resistor. Not sure why this line is low. The only suggestion I have is to measure Vcc going to the Intel microcontroller to see if this voltage level looks okay. As long as this line from the microcontroller is pulled low T011 and ZTX751 transistors are not going to turn on so no 12V pullup voltage for the switches. I'm just hoping the Intel part isn't damage and it's a power problem or some other input to this chip that's repairable. It's possible the bad output of the 2950A voltage regulator could be impacting the controller but I just don't know. The output of the VR goes to the dual comparator LM2903 chip but from there I can't follow all the traces. Could use Bob's input on all this one. Hopefully replacing the 2950A regulator and restoring the 5V output will help.

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With the microcontroller line low the voltage level needed to turn on T011 isn't present so the 751 transistor is also not conducting and no 12V to pullups.

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One additional measurement you might make is with the module powered down is measure the resistance from the trace going to the microcontroller to ground. Measure from the pad left of the pair of resistors to ground. Just want to check if there's low resistance to ground, which would indicate the Intel chip may be damaged, hopefully not. I'm trying to think of a reason if this line from the Intel controller is used to enable and disable these transistors and if so why. Just wondering what would be a reason to turn off these transistor and the pullup voltage to the switches. If the microcontroller is not damaged for what reasons would it turn of the pullup voltage; stored error codes?

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Discussion Starter #183
Thank you Swany for your help and time! resistance from pad in above picture to ground is 7.6 kilo ohms, which is ok I think, what do you think?

If we are thinking about 5V regulator, then is there any reason why there isn't 5V on output except that regulator is bad? What about that 149 kilo ohms resistance to ground?
 

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Thank you Swany for your help and time! resistance from pad in above picture to ground is 7.6 kilo ohms, which is ok I think, what do you think?

If we are thinking about 5V regulator, then is there any reason why there isn't 5V on output except that regulator is bad? What about that 149 kilo ohms resistance to ground?
The 7.6K to ground means there's not short to ground on that line so that's good. Measure the supply voltage to the chip when you can see what that voltage is.

Because you measured a high resistance to ground for the output of the regulator I'd say the only other thing it would be is the input voltage but it is the 11.2V supply voltage and that's present. I can't tell what the 5V from the regulator is used for, it's an input to the comparator but I don't know what it's being compare with and how the output is being used.
 

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Ryan, as mentioned in previous posts the Intel microcontroller line being low it preventing 12V pullup supply transistors from turning on and I found a path from the LM2903 dual comparator device to the Intel microcontroller that may be impacting the microcontroller. The 5V output from the 2950A voltage regulator is a known problem and this output is a voltage reference input into the LM2903 comparator device so replacing the 2950A VR device may solve the the other problem with the microcontroller line being low when it should not be.

From the photo pin 1 output A goes of the comparator chip goes to the Intel chip and I need your help tracing the inputs of comparator A. Pin 2 and pin 3 are the inputs that determine the A output on pin1 but I can't follow these traces, they're underneath the chip. If you could do some continuity measurements from pin2 and pin3 to the backside board traces and find out what traces these pins connect it will help me understand if the low 5V output from the voltage regulator is the problem. The 5V reference voltages does go to a comparator B input but I need to know if also goes to one of the A comparator inputs.
For the comparator device I've traced pin1(outA), pin4(grd), pin5(nonINV B), pin6(INV B) and pin8(V+) but I can't trace pin2,3 and pin 7. If you could determine the traces that connect to these pins it would be appreciated.

I do think if replacing the 2950A voltage regulator restores the 5V output there's a good chance it may solve this other problem with the transistors that enable the 12V pullup voltage to the switches.


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Discussion Starter #186
Hi Swany! Thank you very much, that is great job you did there! I will do continuity measurements and track the rest of the traces. Could you please send picture of LM2903 comparator in higher resolution. It is impossible to read what you have labeled there.
 

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Hi Swany! Thank you very much, that is great job you did there! I will do continuity measurements and track the rest of the traces. Could you please send picture of LM2903 comparator in higher resolution. It is impossible to read what you have labeled there.
I know the pictures are not very clear but are the best I can do with this section of the board. Although not all that important I wanted to know where pins 2,3 and 7 are connected on the back side of the board. I placed circles with question marks where I think they may go but not sure. Bottom line though there are two comparators in the LM2903 chip and at least one and possibly both outputs go to the Intel microcontroller so a bad/low 5V reference voltage that's an input to the comparator needs to be corrected. When you get the new voltage regulator installed it would be helpful to see the voltage levels on all the pins of the LM2903M device.
Pin 6 of the LM2903 is the V- input to comparator B and this reference voltage is the 5V from the 2950a voltage regulator. This 5V may even be an input to the A comparator but I don't know and why I wanted to know what pin2 and 3 are connected to, which are both inputs to comp A.
 

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Discussion Starter #188 (Edited)
Hi Swany! First of all thank you very much for your time and help. You have done so much, I could not have done it without your help! I don't know how to thank you, it is too bad that we are too far to invite you for a beer!

Second I did the continuity test of found all the missing pins 2,3 and 7. Actually 7 was were you thought 1 will be. Pin 1 I traced and marked in other picture. Please see both pictures (pictures were updated).
LM2903M backside pins.png Chip back 2.jpg
 

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Discussion Starter #189
One more interesting thing after close examination of PCB and components I found that one place which is marked as diode, but "diode" does not look like I diode, at least not any more, however it does not look like there was anything else or it has been resoldered. I have attached picture.
Diode.jpg
 

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Hi Swany! First of all thank you very much for your time and help. You have done so much, I could not have done it without your help! I don't know how to thank you, it is too bad that we are too far to invite you for a beer!

Second I did the continuity test of found all the missing pins 2,3 and 7. Actually 7 was were you thought 1 will be. Pin 1 I traced and marked in other picture. Please see both pictures (pictures were updated).
View attachment 2612820 View attachment 2612818
Thanks for finding the missing pins, very helpful. I do have a couple of questions based on your pictures.

You have pin2 with continuity to ground, I wouldn't expect this but I don't know for sure. You also have pin2 labeled on the bottom pad with question marks and this trace goes to the other side of the capacitor (C045) which I would not expect to be grounded, the other side is clearly going to ground. If there is continuity across the capacitor legs I would consider this a possible problem. I have circled the two places I would like you to check to help confirm which pins on the LM2903 these two circled areas go to. Can you also check the two areas circled and pin 3 for continuity back to the voltage regulator ouput (pin6)? Just want to confirm if VR output goes anywhere else. Thanks. I'm attempting to understand comparator A inputs (pins 2 and 3) and can't make sense of what's being compared but still don't know what's going on with pin 2. There's a two resistor voltage divider but not sure of the voltage supply being looked at.
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Discussion Starter #191
Thanks for finding the missing pins, very helpful. I do have a couple of questions based on your pictures.

You have pin2 with continuity to ground, I wouldn't expect this but I don't know for sure. You also have pin2 labeled on the bottom pad with question marks and this trace goes to the other side of the capacitor (C045) which I would not expect to be grounded, the other side is clearly going to ground. If there is continuity across the capacitor legs I would consider this a possible problem. I have circled the two places I would like you to check to help confirm which pins on the LM2903 these two circled areas go to. Can you also check the two areas circled and pin 3 for continuity back to the voltage regulator ouput (pin6)? Just want to confirm if VR output goes anywhere else. Thanks. I'm attempting to understand comparator A inputs (pins 2 and 3) and can't make sense of what's being compared but still don't know what's going on with pin 2. There's a two resistor voltage divider but not sure of the voltage supply being looked at.
View attachment 2612825
Here are the results, please see picture. One of the circled places has continuity to Pin2, but not ground. The other has no continuity to any of the pins of LM2903. Also from resistor leg where pin3 goes, there is no continuity to LM2903 pin6, nor to VR output.
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Thanks again Ryan and just to clarify, the top side leg of the capacitor where I have the red ground label you have label that point as pin2 and you also have the bottom leg of the capacitor as going pin 2 but not to ground. The top leg of the capacitor is connected to the ground plane so I'm confused why this leg of the capacitor would go to pin2 and even if pin2 is connected to the top cap leg (ground) how can the bottom leg of the capacitor also be connected to pin2 but not ground? Is there continuity between the two cap legs? If so, like I mentioned before this would be a problem. Can you check continuity across the capacitor legs and let me know.

I had a picture attached with two points I wanted you to check for continuity but it was incorrect. I'll post again when I have it corrected. I'm still trying to find out what voltage level is connected to pin2, which in an input for comparator A.
 

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Discussion Starter #193
Thanks again Ryan and just to clarify, the top side leg of the capacitor where I have the red ground label you have label that point as pin2 and you also have the bottom leg of the capacitor as going pin 2 but not to ground. The top leg of the capacitor is connected to the ground plane so I'm confused why this leg of the capacitor would go to pin2 and even if pin2 is connected to the top cap leg (ground) how can the bottom leg of the capacitor also be connected to pin2 but not ground? Is there continuity between the two cap legs? If so, like I mentioned before this would be a problem. Can you check continuity across the capacitor legs and let me know.

I had a picture attached with two points I wanted you to check for continuity but it was incorrect. I'll post again when I have it corrected. I'm still trying to find out what voltage level is connected to pin2, which in an input for comparator A.
My apologize, I mistyped. Here is the correct pin position.
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My apologize, I mistyped. Here is the correct pin position.
View attachment 2612884
Thanks

I think the eyelet area with the no continuity label goes to someplace under the OKI chip. From there I can't determine where it ends up. I was attempting to draw the circuit and understand what comparator A is doing, output does go to pin 35 of the Intel microcontroller. Comparator B looks like is comparing a voltage divided 12V level with the 5V from the voltage regulator but can only follow the output to underneath the Intel chip, can't determine where it goes.

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Discussion Starter #195
I traced that "no continuity" eyelet to the far right side of the PCB. This track came out under the OKI chip, then went back and then came back again. Please see pictures ( I removed the sticker, but didn't take new photos), you can see where it "normally" surfaces on the diode leg.

Eyelet X 1.jpg Eyelet X 2.jpg
 

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I traced that "no continuity" eyelet to the far right side of the PCB. This track came out under the OKI chip, then went back and then came back again. Please see pictures ( I removed the sticker, but didn't take new photos), you can see where it "normally" surfaces on the diode leg.

View attachment 2612906 View attachment 2612907
It look like this line is the vehicle speed signal (Y.35), which is good to know since it likely eliminates this comparator (comp A) as the cause of the low signal coming from the microcontroller and neither of the comp A inputs use the voltage regulator 5V as an input.

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The output of comparator B, which does have the 5V from the VR as an input goes to an eyelet that's underneath the Intel microcontroller so I don't know where this trace ends up. Also don't know for sure is this signal output is related to the other problem with the pullup voltage and microcontroller low signal but comparator B output is dependent on the 5V from the voltage regulator, one of the inputs to comp B, the other input being a voltage divided level from the 12V supply.

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Hi Ryan, next chance you get can you help me confirm a connection, which pin the circled eyelet goes to. I had originally thought it went to pin 31 (P2.7) the third pin from the right in the top row but it also looks like it may go to pin 32(PSEN), the forth pin from the right. Just trying to see what makes sense and why the one pin (PSEN?) is low when it should be high. It would make more sense if it's pin PSEN and not P2.7. This is the signal going to the transistors that controls the 12V supply for the switch pullups.
Next time you're able to measure voltages I'd be interested in the input and output levels of the two LM2903 comparators. One of the outputs I still don't know where it goes but still would like to know the levels to help me understand the circuit and what may be a problem, or not. Not certain the new voltage regulator will fix the problem because I don't completely understand the circuit but thanks to your previous measurements I have a better understanding of what's going now, which should help with next steps. At least we know the one signal level that isn't correct and can work backwards to find the cause.

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Discussion Starter #198 (Edited)
Finally got the new 5V regulator, soldered it and now for a very short period of time (10-20 seconds) there is 5V on the output after N52 is powered up. Then regulator starts to heat up and voltage drops quite fast to 2V, I would say in 20-40 seconds, I watched that on multimeter. At that point regulator is so hot one can't touch it. I can't tell if the capacitor (at least I think it is capacitor, please see picture) on the other side of the PCB heats up by itself, meaning it is bad/shorted and is draining completely 5V regulator, hence heating it up. Or the capacitor is just close to the regulator and heats up from the regulator. I tried to feel other parts of the PCB and no other component was heating up. When N52 is powered down and both components cool down and N52 is powered back on there is 5V on regulator output again and then it regulator starts to heat up and voltage drops to 2V.

I measured collector of the ZTX751 and there is still 1.5V. No changes to voltages on the legs of transistor T011. Got your message late, so didn't measure voltages on LM2903 in/out, next time will do for sure. I will try to track eyelet continuity you asked in post 197 tonight.
Capacitator.jpg
 

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Finally got the new 5V regulator, soldered it and now for a very short period of time (10-20 seconds) there is 5V on the output after N52 is powered up. Then regulator starts to heat up and voltage drops quite fast to 2V, I would say in 20-40 seconds, I watched that on multimeter. At that point regulator is so hot one can't touch it. I can't tell if the capacitor (at least I think it is capacitor, please see picture) on the other side of the PCB heats up by itself, meaning it is bad/shorted and is draining completely 5V regulator, hence heating it up. Or the capacitor is just close to the regulator and heats up from the regulator. I tried to feel other parts of the PCB and no other component was heating up. When N52 is powered down and both components cool down and N52 is powered back on there is 5V on regulator output again and then it regulator starts to heat up and voltage drops to 2V.

I measured collector of the ZTX751 and there is still 1.5V. No changes to voltages on the legs of transistor T011. Got your message late, so didn't measure voltages on LM2903 in/out, next time will do for sure. I will try to track eyelet continuity you asked in post 197 tonight.
View attachment 2613028
Finally got the new 5V regulator, soldered it and now for a very short period of time (10-20 seconds) there is 5V on the output after N52 is powered up. Then regulator starts to heat up and voltage drops quite fast to 2V, I would say in 20-40 seconds, I watched that on multimeter. At that point regulator is so hot one can't touch it. I can't tell if the capacitor (at least I think it is capacitor, please see picture) on the other side of the PCB heats up by itself, meaning it is bad/shorted and is draining completely 5V regulator, hence heating it up. Or the capacitor is just close to the regulator and heats up from the regulator. I tried to feel other parts of the PCB and no other component was heating up. When N52 is powered down and both components cool down and N52 is powered back on there is 5V on regulator output again and then it regulator starts to heat up and voltage drops to 2V.

I measured collector of the ZTX751 and there is still 1.5V. No changes to voltages on the legs of transistor T011. Got your message late, so didn't measure voltages on LM2903 in/out, next time will do for sure. I will try to track eyelet continuity you asked in post 197 tonight.
View attachment 2613028
It does sound like the cap is damaged/shorted and pulling down the 5V regulator output. Most likely what fried the previous one. Desolder this cap power it back and see what happens. The cap should not be heating up. If the regulator is still getting hot, which I don't think it will, then there could be a problem with the LM2903 chip but I suspect it's the capacitor.
 

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Discussion Starter #200
Circled eyelet in the picture goes to 31 (P2.7) the third pin from the right in the top row. If you are interested it goes to other side, back and then back again. On the other side in connects to circled pad in the picture.
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