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Help With automotive gauge cluster

Rob_D

Dec 22, 2022
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Hi guys I'm working on a bit of a puzzle. A while back my tachometer was reading erratically so I followed a YouTube video and reflowed the solder to a few chips which seems to have fixed it. Those chips were the lower horizontal multi-pin chips, 2 per side.

My next problem was a loss of power to the odemeter and gear indicator display which another video said was powered by 2 MOSFETs (circled)that need to be resoldered in most cases and the square IC towards the bottom middle of the board.

The power issue worked for about 30 miles. I'm considering changing out the MOSFETs but a search for the exact numbers comes up blank. Can someone help me with maybe a testing procedure to see if they are bad and then what I need to look for as far as a replacement?

Also if someone can help me with a general explanation of what the horizontal chips do?

I know I can just send this out for repair but I've always wanted to learn components.PXL_20220824_181839258~2.jpgPXL_20221221_191537671.jpg
 

kellys_eye

Jun 25, 2010
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The chips will have codes on them that are usually discoverable at various datasheet sites like www.alldatasheet.com using their search engine. I'd hazard a guess (since I can't read the numbers) that they are stepper drivers intended to drive the pointers on the dials which themselves are attached to small motors.

The FETs will either work or not - they don't do 'intermittent'. Removing them from circuit and using a tester is (perhaps) the most reliable method of testing - the cheap chinese component testers are more than capable of both testing them and showing you the leadouts. Most FET's, when used in this type of application, are interchangeable provided you get one that has an equal or better spec (in terms of voltage/current capacity) and gate operation voltage (many are 'logic level' type FETs).

You quite sure it's a power loss issue? Have you checked to see if the display is receiving the right data? Loss of data would cause the needles to drop to 'zero'. Check the connectors to see how/where the data is being applied to the display panel and that the connections are all clean and effective.
 

Rob_D

Dec 22, 2022
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Dec 22, 2022
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The chips will have codes on them that are usually discoverable at various datasheet sites like www.alldatasheet.com using their search engine. I'd hazard a guess (since I can't read the numbers) that they are stepper drivers intended to drive the pointers on the dials which themselves are attached to small motors.

The FETs will either work or not - they don't do 'intermittent'. Removing them from circuit and using a tester is (perhaps) the most reliable method of testing - the cheap chinese component testers are more than capable of both testing them and showing you the leadouts. Most FET's, when used in this type of application, are interchangeable provided you get one that has an equal or better spec (in terms of voltage/current capacity) and gate operation voltage (many are 'logic level' type FETs).

You quite sure it's a power loss issue? Have you checked to see if the display is receiving the right data? Loss of data would cause the needles to drop to 'zero'. Check the connectors to see how/where the data is being applied to the display panel and that the connections are all clean and effective.
Thanks for the reply. After a couple of drive cycles I think I have two different issues.

#1 seems to be a global power issue on the board which is "new" following previous repair attempts. Possibly have a cold joint on one of the MOSFETs upstream? This seems to manifest after about 40 minutes of driving and I'm assuming may be when the board warms up. The reason I think it's power and not loss of data is how the cluster reacts, it seems to cycle on and off more rapidly until it finally remains off for the rest of the drive.

#2 Is characters in the odometer display that should not be present. In the picture below it should read "C-CODE". I'm assuming this is due to either a solder bridge or cold joint on the quad IC towards the bottom of the board that I tried to reflow.

Question 1: Can MOSFETs exhibit this behavior due to a gradual overheating?

Question 2: I googled the chip numbers and one is a J127 which seems to be a readily available piece. The other "MOSFET" is listed as a linear voltage regulator. Is this still just a MOSFET or is it a specific type of MOSFET?
 

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Alec_t

Jul 7, 2015
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The other "MOSFET" is listed as a linear voltage regulator. Is this still just a MOSFET or is it a specific type of MOSFET?
A linear voltage regulator is not the same thing as a MOSFET. However, it may well include a MOSFET as part of its circuitry.
 

kellys_eye

Jun 25, 2010
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Linear voltage regulators are as their description - usually converting one DC voltage level to another i.e. 12V down to 5V as an example.

They are very common and readily available although a quick test of their input and output voltages will show if they are working as intended.

As to the loss of signals, remove the board to the workbench and use a hot air gun to warm the board whilst measuring voltage(s) at strategic points. Keep a can of 'freezer spray' handy to squirt at individual locations to get the missing power back and you'll eventually reduce the area of concern to somewhere that resoldering will make a difference.
 

davenn

Moderator
Sep 5, 2009
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The other "MOSFET" is listed as a linear voltage regulator. Is this still just a MOSFET or is it a specific type of MOSFET?

so what are the markings on it ?
 
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