IGBT question - Page 1
Forum section: electronics / beginners

author: mw52563
author_rank: Contributor
timestamp: April 26, 2020, 03:19:16 pm
content: Hi,Hoping someone can help me (again)... trying to get a treadmill PCB working. I identified what I thought was a dead IGBT (havent done electronics since Uni so I cant really remember how they work or how to test them.Anyway this is the IGBT I took out of the boardAnd this is the datasheet for ithttps://pdf1.alldatasheet.com/datasheet-pdf/view/245105/FAIRCHILD/FGH20N60UFD.htmlI checked it with a multimeter and theres also a 27.7 ohms resistance between pin 1 and 2I then replaced the IGBT with the following IGBT (there was 5 in a pack so ive got some spares)GW20V60FG4 029 V5CHN G4 339.Ive taken this one out and theres a short between every pin, so I guessing the board has fried it?I believe this is the datasheet for ithttps://www.st.com/resource/en/datasheet/stgw20v60f.pdfThis is one of the new ones that I havent used yetTheres not a short over any of the pinsThanks for any helpMike

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 26, 2020, 03:34:27 pm
content: There should never be continuity between the gate (pin 1) and anything else. The gate is insulated from the rest of the transistor by a thin layer of silicon dioxide. Normally there will be a diode drop between the other two pins but this isn't necessarily so.A shorted out switching component is usually a symptom rather than a cause. Something bad has happened and the transistor has melted and shorted out entirely. So the diagnostics should include trying to find out why the switching device failed. If the failure can't be identified and corrected with certainty, there is a trick you might use to possibly save the next switching component. Place a reasonable wattage light bulb in series with the load and power it up. If there is a dead short, the light bulb will prevent too much current running through the switching component. It will also glow brightly.I would start by checking the motor. It's a permanent magnet DC motor right? Check for continuity between the motor leads and case and shorted armature windings.

author: mw52563
author_rank: Contributor
timestamp: April 26, 2020, 04:51:26 pm
content: yeh its a DC motor but it works fine, ive tested it by its own. Why do you think the new one is showing up as a capacitor?RegardsMike

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 26, 2020, 05:16:33 pm
content: Remember I said the (aluminium) gate was insulated from the rest of the semiconductor by a thin layer of silicon dioxide? That makes the gate a capacitor too. The gate capacitance is a big deal especially on larger devices, well into the nF. In fact turning these devices on and off rapidly gets to be difficult since you're essentially charging and discharging a capacitor.Diagnosing from here gets difficult without some pretty decent equipment. For example at this point I would be curious to see what the gate is seeing relative to the emitter without the IGBT installed but for that you would need differential probes and an oscilloscope. With limited equipment I might poke around checking some of the line input components with the unit powered off. Photos of the PCB might help.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 26, 2020, 08:11:32 pm
content: Right, there's almost always something that caused the transistor to fail.From a design standpoint, a lack of adequate protection is a possible root cause (though one that's not very helpful for repair purposes). Check everything around the transistor: source, load, gate drive. Possible failure modes include faulted or intermittent load, buck diode or opposing transistor, burned out snubber network, failed supply bypass capacitors, excess supply voltage, burned gate driver chip, open or intermittent gate drive resistor, etc.Tim

author: mw52563
author_rank: Contributor
timestamp: April 26, 2020, 09:35:51 pm
content: HiThanks for all the replies... its much appreciated. I did post this picture a few days ago. It appears one of the legs of the component is missing. But no one seemed to know what the component was.

author: mw52563
author_rank: Contributor
timestamp: April 26, 2020, 09:45:43 pm
content: And this is the actual board

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 26, 2020, 09:49:29 pm
content: Is much of the board covered in a goopy sort of lacquer? You might not be able to read it because it's seeped into the lettering, try scraping it off (or if possible, using a more aggressive solvent like THF). Would also be interested to know what U1 is.How about a bottom view?Tim