mosfet or transistor?

[MarkM]

Hi guys,
I'm wondering if this is a mosfet or transistor, and the proper way to test it.

Thanks,
Mark

[capkid]

Re: mosfet or transistor?

That's a diode. Perform these testing procedures in diode mode on your meter (pins numbered from left to right). You may have to remove the diode from the board if the readings are funky.

Test 1:
Pin 1 - Pos lead, Pin 2 (or the tab) - Neg lead. Expected Result: Reading of around 0.5V
Pin 1 - Neg lead, Pin 2 (or the tab) - Pos lead. Expected Result: Open or "OL"

Test 2:

Pin 2 (or the tab) - Pos lead, Pin 3 - Neg lead. Expected Result: Open or "OL"
Pin 2 (or the tab) - Neg lead, Pin 3 - Pos lead. Expected Result: Reading of around 0.5V

[budm]

Re: mosfet or transistor?

That is Dual diode with common Cathode (the Cathode of bothe Diodes are tied together) in the middle big tab, the other two pins are the Anode, in this case, they are also tied together by the the circuit traces. So you can just treat and test this as one SINGLE diode.

[MarkM]

Re: mosfet or transistor?

Thanks capkid,
Here's my results of my test, there are two of these diodes on the board..

Test 1: doide1
Pin 1 - Pos lead, Pin 2 (or the tab) - Neg lead. Expected Result: Reading of around 0.5V .046
Pin 1 - Neg lead, Pin 2 (or the tab) - Pos lead. Expected Result: Open or "OL" .OL

Test 2:

Pin 2 (or the tab) - Pos lead, Pin 3 - Neg lead. Expected Result: Open or "OL" 0.000
Pin 2 (or the tab) - Neg lead, Pin 3 - Pos lead. Expected Result: Reading of around 0.5V 0.000

---
Test 1: diode2
Pin 1 - Pos lead, Pin 2 (or the tab) - Neg lead. Expected Result: Reading of around 0.5V .392
Pin 1 - Neg lead, Pin 2 (or the tab) - Pos lead. Expected Result: Open or "OL" .OL

Test 2:

Pin 2 (or the tab) - Pos lead, Pin 3 - Neg lead. Expected Result: Open or "OL" 0.000
Pin 2 (or the tab) - Neg lead, Pin 3 - Pos lead. Expected Result: Reading of around .392

I removed diode 1 from the board to double check and getting the same reading. I take it this diode is bad.

I just took some new readings and I no longer have continuity to ground with the -VY resistor, and also the rings on the ipm as in this thread https://www.badcaps.net/forum/showthread.php?t=30592 . Wonder if this diode caused the ipm to go bad or vs versa. Should I look further for a cause to what blew out the diode?

Thanks
Mark

[capkid]

Re: mosfet or transistor?

According to your testing, both diodes look bad. Did you remove diode #2 from the board to check it?

There's some info here in the description of Coppell's eBay listing:

http://www.ebay.com/itm/20LC30-DIODE...-/160645198095

[MarkM]

Re: mosfet or transistor?

sorry capkid,
for diode 2
where i have
Pin 2 (or the tab) - Pos lead, Pin 3 - Neg lead. Expected Result: Open or "OL" 0.000

it is
Pin 2 (or the tab) - Pos lead, Pin 3 - Neg lead. Expected Result: Open or "OL"
reading is OL

would you still consider this diode bad? (since I'm getting .392)

[capkid]

Re: mosfet or transistor?

Your second diode appears to be fine.

[MarkM]

Re: mosfet or transistor?

Thanks, I went ahead and ordered the diode (and one spare )

Please correct me if I'm wrong.. Voltage flows into the anodes and out of the cathode and blocks it from flowing back(like a check valve)? The two anode spots on the board have continuity to ground. Could something else be bad as well, that trace to the anode spots causing it to ground? Or does it sound right to have anodes as ground?

Thanks

[cashkennedy]

Re: mosfet or transistor?

Are both sides continuous to ground? Is the resistance to ground steady and under 5 ohms? If the resitance fluctuates up might indicate you're actually charging a capacitor that is bridging the anode to ground.

It's possible that the cathode of the bad diode is ground, and its "shorting" the anode side by being a faulty diode that's allowing reverse flow that is basically grounding out the anode side.

[budm]

Re: mosfet or transistor?

"The two anode spots on the board have continuity to ground". That depends on how this diode is being used, if the Anode is connected to one wire of the transformer winding, and the other end of the transformer winding is connected to ground which is typical for half wave rectifying circuit, then you will see very low Ohms reading due to low transformer's winding resistance.
We need to see bigger pictures of this board to see how this Diode being used.
I see you mention Diode 1 and Diode 2, are they the same as shown in the picture?

[tom66]

Re: mosfet or transistor?

Thanks, I went ahead and ordered the diode (and one spare )

Please correct me if I'm wrong.. Voltage flows into the anodes and out of the cathode and blocks it from flowing back(like a check valve)? The two anode spots on the board have continuity to ground. Could something else be bad as well, that trace to the anode spots causing it to ground? Or does it sound right to have anodes as ground?

Thanks

Voltage doesn't "flow"... voltage is sort of like water pressure, and current is sort of like water flow rate. A diode in this case is similar to a valve which only lets water flow in one direction... but it's the "flow rate" it's blocking, not the "pressure" (current not voltage.)

[MarkM]

Re: mosfet or transistor?

Hey guys,

cashkennedy,
Both sides of the anodes traces are continuous to ground. Ohm reading 000.0

The diode is off the board

budm,
I attached two images, one marked up and one not. Yup diode1 and diode2 are the same shown in the picture.

I'm just trying to rule out there's not any other problems before I install the new diode and ipm

thanks guys

[budm]

Re: mosfet or transistor?

The Anode of that D21 (both pins) are connected to the Ground plane, you can see the GND label on the PCB. It looks like it is for Buck regulator switching power supply. Cannot see D11 traces, but it may be the same for another buck regulator.

[MarkM]

Re: mosfet or transistor?

Thanks budm,
Just so I understand, where is the ground label on the board? Is it the dark green mask?

[budm]

Re: mosfet or transistor?

Gnd

[Agent24]

Re: mosfet or transistor?

For the record, a MOSFET *is* a transistor: Metal Oxide Semiconductor Field Effect Transistor...