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Old 11-21-2022, 02:26 PM   #21
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Default Re: 1992 Toyota Truck Speedometer

The zener and transistor are in oddball packages I think, the transistor low height stubby to clear the odometer wheels and the zener is some Japanese JEITA package.
A replacement 9.1V zener for ZD2 could be around 200mW-500mW like 1SMA5924BT3G or BZT52-C9V1 or MMSZ5239 would work.
edit: the power transistor is 2SD2033 (insulated TO-126 ECB pinout).
I don't like this PCB trace, it looks cut. Check them with a multimeter or tin them with solder.

First I would fix the 9.1V power problem. The hot trace or part doesn't make sense, stop running it as the IC is getting overvoltaged - it likes 9V coming in, not 11V or 14V.
I would check for breaks in the PC board traces. Shine a light on the front side and see if you need to add solder to the cleaned up traces to fix some slices or cuts.
The fractured solder joints or "ghost rings" as someone calls them, occur at through-hole part pins and for the hassle I touch up all of those on automotive boards. See sample pics to learn what they look like.
Attached Images
File Type: png fractured joints 002.png (850.0 KB, 8 views)
File Type: jpg fractured joint010e.jpg (31.5 KB, 8 views)
File Type: jpg speedometer trace.jpg (308.0 KB, 9 views)

Last edited by redwire; 11-21-2022 at 03:11 PM..
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Old 11-21-2022, 02:29 PM   #22
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Default Re: 1992 Toyota Truck Speedometer

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Old 12-13-2022, 10:56 AM   #23
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Default Re: 1992 Toyota Truck Speedometer

Thought you guys might like a bit of resolution to this:

Thank you for all the help!
I resoldered the components and replaced the zener. That hot trace cooled off and the correct voltage showed up on pin 16 of the IC. But made no difference to the accuracy of the speedometer.

The final solution was to replace the IC (TB9213) with a "new" 30 year old component.

Again. Thanks for the help. Learned quite a lot.
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