Whats the part pls

[snipersquad100]

Can anyone identify this part pls, Looks like a diode but ive never seen one like this b4. It marked up as T3d37, the last 37 has a - sign  above them. I cant find any info on it. Datasheet would be nice and somewhere I can buy one. Thank you.......

[codeboy2k]

My guess is that it's a transient suppressor (TVS diode) from Shindengen Electric.  Called their "trankiller" series.

I don't know that particular marking code, T3D 37, but a diode in the same series marked T3D 54 is a ST03D-170.

These transient suppressors all begin with ST03D-XXX where XXX is the breakdown voltage.  The ones I know of are ST03D-82, ST03D-140, ST03D-170, ST03D-200

It's a zener and a regular diode face to to face (cathode to cathode), so when you try to read it in diode mode with a multimeter it will either read open (this is good) or shorted (this is bad), or read like a regular PN diode showing 650mV or so (this is also bad). It should always read open, and will never read like a typical 650mV PN junction diode and this may throw you off.

If it reads open, this is good.  To find out which one you have, put it in a test circuit across a current limited voltage (maybe 5mA), and slowly raise the voltage up from 50V to over 200VDC and determine when it starts to conduct. That's the breakdown voltage you have. It will be close to those voltages I listed.

You might assume if the T3D 54 is 170V , then the T3D 37 might be 140 or 82 VDC.  This could be right, or wrong. Where you got it from (i.e. how it was used in circuit) might also help you decide what its breakdown voltage should be.



http://www.shindengen.co.jp/product/semi/datasheet/U180_ST03D-82.pdf
http://www.shindengen.co.jp/product/semi/datasheet/U180_ST03D-140.pdf
http://www.shindengen.co.jp/product/semi/datasheet/U180_ST03D-170.pdf
http://www.shindengen.co.jp/product/semi/datasheet/U180_ST03D-200.pdf

[snipersquad100]

I had it out of a power supply from a dvd player that wasn't working, the fuse on the board was blown so I put a new one in and pluged it in, and BANG lol,  MIP3E3SMY exploded I've ordered a new one of those but I was checking the surrounding parts as well hence checking T3D37, but wasn't sure what it was. Thanks for the feedback I will test it later, cheers

[snipersquad100]

HI, I found the schematic and the diode in question is 300W 70 volts but the symbol on the schematic just shows a normal diode.

[snipersquad100]

170 v sorry

[codeboy2k]

Please cut and paste the relevant section from the schematic so we can see how it's wired. That will make it clear too, whether it's a basic diode or a TVS diode.  Power diodes like would be used in a power supply are in series with the line... TVS diodes are paralleled across the line to ground.

[snipersquad100]

Hi, sorry for late reply. I will post the schematic below but I have fixed the problem, it was the MIP3e3smy. The person who give it to me said it never worked from new, I don't know why she didn't take it back. I did notice that there was a track running between pin 1 & 2 of the mip3e3smy which was very thin and they needed to tin the track with solder which made it exposed (no solder mask) and I was thinking that there might of been a voltage jump across that track and pin 1 as the track was closer to pin1, why they didn't centre it in-between pin 1 & 2 I don't know, so I put some hot snot over the the pins to try and insulate the track. Anyway I changed the mip3e3smy and a zener diode zd101 to a 1n4148 and it works fine now. A nice dvd player for £4.50.
   I was wondering if I could use something other than a mip3e3smy but I could only get a datasheet in Chinese so I just went with the same chip. Anyway job done and thanks for the help.

[snipersquad100]

Sorry wrong schematic, that's a different model this is the right one. Ic101 is the part at fault, D103 is the part I wasn't sure about, Zd101 is the zener I changed.

[codeboy2k]

Good that you got it working.. I'm actually surprised that you said you replaced the zener diode ZD101 with a 1n4148, that's just wrong. The transformer winding marked B1 and B2 is the bias winding, it's a secondary winding really, that provides startup voltage and bias voltage for the  MIP3E3SMY device, which is a 3 terminal flyback controller from Panasonic, licensed from Power Integrations, Inc.  It's not simply a MOSFET, although it has a power MOSFET inside it. The B1 and B2 of the transformer is the bias winding, it is a secondary winding, and the voltage produced is half-wave rectified with a standard diode D102, and filtered with C110. Then the zener diode that you replaced with a standard 1N4148 is supposed to limit the rectified and filtered voltage to 12V.  That diode ZD101 is a MA4120, a 12V zener.  If you put a regular diode there, in the same orientation, it's just going to be reversed biased and do nothing at all, so of course it works, it's like the zener is not there anymore, and so the voltage may be too high now.  If you carefully measure the voltage across the new diode you put in, you might find that it's above 12V. This may or may not hurt the MIP3E3SMY controller, I don't know. You would be wise to find a proper 12V zener and put it there, to keep it from future damage.

The original diode you had a question on is definitely a TVS device, as I said previously.  It's drawn as a simple diode in the schematic, but it's really a diode and a zener as I explained. It's across the primary winding so that it can act as a freewheeling diode, for back EMF voltages above 170V, which may be generated when the MOSFET turns off.

[snipersquad100]

ahh ok. That zener diode I pulled out was showing a voltage drop each side so I thought it might be faulty and I only had a 1n4148.
I will replace it b4 I use it. You was right about the other diode it was open both ends and it works fine.