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I usually fix consoles, as a hobby more than anything, but have been asked to have a look at something as a favour. It is a simple PCB, but it is really old and the manufacturer has stated they no longer have schematics.

It is a control module for a plant vehicle. When plugged in, it blows a fuse in the vehicle. Having gone over the PCB, I think I have identified the issue. There are 2 diodes labelled Z2 and Z3. I believe they are Zener diodes. There is no band on the diode, but there is on the PCB. The top line of text reads 1.5KE33CA. The bottom row reads 0220K.

Would anyone please be able to tell me where I might find a replacement? They are both identical. I am only using a cheap Draper multi meter, but putting it in diode mode, one of the diodes appears to have an open line in both directions, or at least the reading drops from 1 to 0 in both directions. The other one remains on 1 in both directions.

photo of PCB with components marked

photo of PCB with components removed

photo of removed component

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    \$\begingroup\$ You can add images. Edit your question, then click the icon that looks like a mountain. That'll let you add images. \$\endgroup\$
    – JRE
    Dec 14, 2020 at 21:46
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    \$\begingroup\$ The diode that shows "0" in both directions is shorted. \$\endgroup\$
    – JRE
    Dec 14, 2020 at 21:46
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    \$\begingroup\$ You'll have to take it off the board to be sure, though. The diode itself may be OK, but something connected to it may be shorted. \$\endgroup\$
    – JRE
    Dec 14, 2020 at 21:48
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    \$\begingroup\$ "0" on diode test means shorted. "1" all the way to the left means "voltage out of range." A number would be the forward voltage of the diode. The one that reads "1" all the time would be bad for a normal diode, but for a TVS it may be OK. \$\endgroup\$
    – JRE
    Dec 14, 2020 at 21:49

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You're in luck! 1.5KE33CA is a part number for a TVS diode. TVS diodes are not Zeners, but they are the kind of thing which appears on PCBs used in vehicles, especially where wires come onto the PCB. They are used to protect the PCB from transients, and this one is about the right size to protect a 24V system. Since this specific part is a bidirectional TVS, it should test as open in both directions with a typical handheld meter. The one which tests as 0 in both directions is probably toast, but it would be best to test it off the board to make sure it is that and not something else.

It's a sufficiently common part that most distributors carry them. My usual go-to has 1700 in stock and sells a bag of five for £3. Other suppliers will also be available.

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    \$\begingroup\$ Wow, I can't thank you enough. Firstly for such a helpful answer and secondly for such a quick response. I have removed them from the board and yes, one has a 0 in both directions, the other no change to the display, just remains at 1. The board has a number of components listed as D1 D2 D3... and just 3 listed as Z1 Z2. I just assumed the Z denoted a Zener diode, but the D components are small surface mounted components and the Z components are through hole cylindrical. Appreciate the help so much. I'll order some replacements now. \$\endgroup\$
    – Ben Coogan
    Dec 14, 2020 at 22:15
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    \$\begingroup\$ @BenCoogan - Hi, (a) FYI, as it says on the datasheet linked in this answer: "Typical failure mode is short from over-specified voltage or current". So seeing a shorted TVS is common after it has been overloaded. (b) That specific part number is a bi-directional TVS - that is why it doesn't have a "band" indicating the cathode (which a uni-directional TVS would usually have). (c) You are encouraged to "accept" (green tick) the best answer (as described here) to mark the problem as solved. (See more info in the tour & help center) \$\endgroup\$
    – SamGibson
    Dec 14, 2020 at 22:32

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