Zener Diodes & Reading Colour Codes - Sega PCBs

[Berty]

I'm working on a Sega motor control board\ from a G-Loc and there a lot of components that need replacement due to corrosion. I'm stuck decoding what a specific compoment is and I need the help of someone more learned than I. On the PCB, there is the following symbol;

 

 

The prefix for the PCB location is a "Z" so I *think* this is meant to be a Zener Diode. It has four colours from left to right, Orange, Orange, Orange Black on the diode (if it is a diode). Can anyone help me confirm if this is indeed a Zener Diode and what the colour code might be as I need to replace a few of them but I am not sure what to order.

 

If the colours are based on the JEDEC codes and if it is a Zener Diode, then I *think* that it is a 1N3330 Zener Diode?

 

[Arcade King]

I believe its a TVS diode a type of Zener.

https://electronics.stackexchange.com/questions/233600/differences-between-tvs-diode-and-zener-diodes-in-diagrams-and-in-practice

[Berty]

Thanks for the reply. I've been doing some reading on the TVS Diodes and their application. In short, it seems like they are used for circuit protection and to prevent voltage spikes. This makes sense given what I am working on. The motor control board is connected to two, high current power control boards that have their own independent AC to DC conversion.

 

Here is a picture of the board in question with the diodes called out.

 

Here is a better picture of the board.

 

 

And the diode itself...

 

 

I've tried to test these using my DMM and I don't get a resistance value, nor do they seem to work in diode test mode.

[Berty]

So, one end of the component (the end with the orange bands) is connected to the 5V traces and the end with the black band is connected to the ground traces in the PCB. Edited June 26, 2020 by Berty

[cwispy]

The symbol is typical for a bi-directional TVS Diode (transient voltage suppression diode), sometimes referred to as transorbs. A bi-directional TVS Diode is basically two diodes which are connected Cathode to Cathode across the power rail and as such it will not read anything when it is good. When they fail, it is typical for them to short the power rail causing a fuse or some other form of protection to blow. Edited July 1, 2020 by cwispy

[Berty]

Thanks Cwispy & AK for the tip of TVS diodes.

 

I'm just trying to figure out what value to get now.

 

Cheers

[cwispy]

What voltage do the motors run at?

 

My best guess is that its a 33C TVS diode based on its markings.

 

Breakdown Voltage

Min: 31.4

Max: 34.7

 

Stand-Off Voltage: 28.2

Maximum Peak Current: 8.8A

Maximum Clamping Voltage: 45.7

[Berty]

Thanks. I was hoping that the colours confirmed to the jedec codes. I need to find out the motor voltage. They are in an G-Loc deluxe.

[Berty]

Plot twist... I have tested the component in two different testers. On both occasions, the test reports back a 33nF capacitor. Thoughts?

 

 

 

 

[cwispy]

Are these devices connected across the power rails of the IC's? From the locations on the picture in the first post, I would have said they were caps, but because you posted that they have the tvs diode symbol, I went with the symbol. If they are only across the 5v supply, then I would say they are capacitors as per the component tester.

[Berty]

Are these devices connected across the power rails of the IC's? From the locations on the picture in the first post, I would have said they were caps, but because you posted that they have the tvs diode symbol, I went with the symbol. If they are only across the 5v supply, then I would say they are capacitors as per the component tester.

 

Hi mate, sorry I didn't mean to throw you a red-herring! I too was confused by a. their appearance (the black line resembled what I thought might be an anode marker) and b. the symbol on the PCB made me question what they were.

 

Given that all other capacitor locations on the PCB have a "C" code and these had a "Z" I was left second-guessing too.

 

Yes - they are across the power rails. I thought that based on this board being connected to a particularly "dirty" AC power supply, the TVS diode thing makes sense.

[Berty]

So I am having issues with finding a 100% like to like replacement. I bought some axial film capacitors that are 33nf +/- 20% but they are too big. Could I just use a standard, single layer ceramic capacitor like these?

 

https://www.jaycar.com.au/33nf-50vdc-ceramic-capacitors-pack-of-2/p/RC5354

[cwispy]

I dont see any reason why not. It looks like they are simply there to smooth the power for the logic chips.