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Repaired temp compensating board 200 86

posted by  someone claiming to be Don Foster on  Sun Oct 22 04:25 CST 2000 [RELATED]

After driving for 3 months with a dead temp gauge, I finally dived into the compensating board.

Yes, I first checked the other stuff—thermostat, voltage regulator, sensor, wiring, connections, and even the gauge. All were OK.

I replaced the LM2902 quad op amp and the PNP transistor on the comp board, and —— temp gauge back to normal! I don't know which of the two was at fault, but since I have a supply of each part, I didn't care to spend the effort debugging to the actual part. In goes the new, out goes the old.







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    Re: Repaired temp compensating board 200 86

    posted by  someone claiming to be chris herbst on  Sun Nov 12 13:02 CST 2000 [RELATED]

    Oh beautiful. This has been the week of fixing things one week before they're posted to the brickboard.

    I just bought 2 temp compensating boards for $30 apiece.

    I just fought front bushings too.

    Well, anyway, I saved the old boards... maybe I'll mess with them now.







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    Another success. 200 86

    posted by  someone claiming to be Jarrod on  Sun Nov 12 07:19 CST 2000 [RELATED]

    I replaced the PNP with radio shack catalog part # 276-2023, the MPS2907 transistor. They did not stock the "LM2902 quad op amp" but they have it in the catalog. I decided to try by just replacing the PNP and it worked!

    Don Foster sent me this diagram which may help you figure out the lead placement when soldering:

    Thanks for the help Don.

    I think this is one of the coolest things I've learned on this site. The PNP is $.65, while the compensator board is over $50 I'm told.

    /Jarrod

    P.S. While at radio shack ask for the cue cat. Beware of Cue Cat's privacy issues. Regardless, it's a free bar code scanner which may be useful. For example, I hear some guy made a book ISBN scanner.







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    Re: Repaired temp compensating board 200 86

    posted by  someone claiming to be Jarrod on  Thu Oct 26 02:39 CST 2000 [RELATED]

    Wow. Thanks.

    I suppose you just figured that when a board fries it's usually compnents like these that fry?

    I have two of these to fix. One for me and one for a friend.

    Time to dig out the soldering iron.

    /Jarrod







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      Re: Repaired temp compensating board 200 86

      posted by  someone claiming to be Don Foster on  Thu Oct 26 12:49 CST 2000 [RELATED]

      "...suppose you just figured that when a board fries it's usually compnents like these that fry?"

      Not really. The board has only a few active components—the quad op-amp, transistor, and two or three diodes. The LM2902 and transistors are the most likely, and diodes don't usually fail.

      Basically, I guessed.

      If you want I'll post a sketch showing orientation of the replacement parts.







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        Re: Repaired temp compensating board 200 86

        posted by  someone claiming to be Jarrod on  Sat Nov 11 09:29 CST 2000 [RELATED]

        That would be great.

        I'm going to take a shot at this tomorrow.

        /Jarrod







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    Re: Repaired temp compensating board 200 86

    posted by  someone claiming to be dave lotman on  Tue Oct 24 03:43 CST 2000 [RELATED]

    Thank you Don,

    I missed your post and after looking at my friends board and seeing the

    parts we also were planning on replacing those parts. Plus there is a cap

    on there that may go bad after a few years of use also. Boy, and those

    parts cost about what $4?

    Its great to have someone that is very comfortable with

    the electronics of these cars. I'm very good with electrical stuff but still don't know all the nooks and crannies.

    Thanks again, are you going to be a Rockleigh?

    All the best,

    Dave.







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      Re: Repaired temp compensating board 200 86

      posted by  someone claiming to be Don Foster on  Tue Oct 24 13:28 CST 2000 [RELATED]

      Dave --

      "...a cap on there that may go bad..."

      Yes — the capacitor acts as an integrator, which slows down the response of the meter. If the cap opened, the meter would simply respond faster.

      "...parts cost about what $4?"

      Don't know. I have a bag of LM2902 op-amps, and another bag of generic replacement transistors. Singly, these probably cost several dollars. But in industrial quantities, they probably cost about $0.00416583 each.

      Check at Radio Shack.

      "...you going to be a Rockleigh?"

      No time, no time.







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    Re: Repaired temp compensating board 200 86

    posted by  someone claiming to be wbain on  Sun Oct 22 14:46 CST 2000 [RELATED]

    It's good to know they left the markings on the IC and Xistor. I wonder if the 700's are similar. Keep up the good diagnostic work.






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