Transient-voltage-suppression question

Submitted by Tom on Sun, 06/14/2020 - 07:07

Hello All,

A friend brought me a defective motor system by which the motor was variably driven and in the circuit was a triac. It was open. Upon close inspection there is what appears to be a tvs transient voltage suppresion device in series with the gate! It's about impossible to get any identification info off the device but the pc board has a double diode symbol which looks like two diodes facing each other with a common cathode bar. The other end of the "diode" goes to a capacitor and a relay contact. There is a 3 ohm resistor that is open and a blown npn transistor also. 

I've looked allot for any circuit where a tvs is in series with a componant but could not find any. Does anyone know why this type of device would be in series with a part like this? 

If it is truly not a tvs, then maybe the pc board silkscreen is wrong and this is just an open diode, with its cathode connected to that gate. 

What's the consensus about this?

 

Thanks!

Tom

Provide the schematic diagram

  Joined February 12, 2018      696
Monday at 02:11 PM

Hello,

I tried to post a link to the schematic but it was flagged for aproval, which has not yet happened.

I don't know how to post the jpg here.

Tom

  Joined April 15, 2019      3
Monday at 10:31 PM

You can add the image using IMCE tool in comment tool box or uplod in some jpeg hosting website and provide the link.

  Joined February 12, 2018      696
Monday at 02:11 PM

motor driver2.jpg

Thanks! The parts in the red are those that failed. The part named "DB" is the one that I can't identify. As I mentioned, the silkscreen shows the symbol for a TVS but I can't understand how that part could work in series when it it's normaly in parallel. So I'm thinking it is actually a diode. I can't read the number/letters off it because they are to badly rubbed away. This part has failed open. Thanks for your help!

  Joined April 15, 2019      3
Monday at 10:31 PM

I had a question about portable internet. I'm not even sure if that's the right term but basically I'll be moving into my cousins empty apartment for a month. There's no internet because she's been gone for so long, is there anyway to create like a hotspot that I can use to do work?

  Joined June 20, 2020      1
Saturday at 09:24 PM

Please make a separate post for this.

  Joined February 12, 2018      696
Monday at 02:11 PM

Well to know the DIAC rating the TRIAC partnumber is required. What is the TRIAC partnumber?

  Joined February 12, 2018      696
Monday at 02:11 PM