Electronics > Repair

Help needed identifying a Zener/TVS Diode (Toyota ECU)

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Signal Simon:
I'm attempting to repair a Toyota engine ECU that it seems has had an over-voltage event, possibly failed alternator or loose battery terminal.
I have found two failed diodes, D401 and D402 (Shorted) marked "1E 8D" which just seem like series diodes from the main power supplies, so have fitted 1N4002s in their place.
However my mystery is D404.
From the screen print, it's a Zener and is directly across the internal supply.
One of its circuit tracks has blown open, so there was obviously more than just a bit of a transient.

The diode is marked: T S5225 8.C

The T I'm assuming signifies Toshiba.
It's in a substantial case 10mm diameter and 4mm thick, similar to a Motorola MR751 series.
Can't find any reference online, it obviously isn't a 1N5225

Logic says the Zener(TVS?) voltage should be in the region of 18 to 24Volts

Any help appreciated

Thanks,
Simon.

fzabkar:
This vendor rates it at 27V 3W, if you can believe it:

https://www.lazada.vn/products/voltage-regulator-s5225-zener-3w-27v-thao-may-test-ok-i2423357599.html

Here is a discussion about a circuit that uses this diode:

http://www.subaru-svx.net/forum/showthread.php?t=59362&page=2

The diode appears to be D4 in this circuit diagram (D4 is a place holder):

http://www.subaru-svx.net/forum/attachment.php?s=76c57ef43ebf18a1041f22109cc5937f&attachmentid=16095&d=1331498282

The IC (μPC1251) in that diagram has a maximum supply rating of 32V:

https://www.renesas.com/us/en/document/dst/upc1251-upc358-datasheet

Jeff eelcr:
These type parts are used in many OEM vehicle modules for overvoltage protection and reverse voltage protection, voltage rating is usually around 27V.
Most of the time they are failed shorted blowing fuses if they are defective and did their job to protect unit from further damage.
Not to say failure is common it is not but is most likley if above conditions are met.
You did not say year made but capacitors are a common problem in many of these units.
Jeff

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