MJ10000 transistor testing. - Page 1
Forum section: electronics / repair

author: electronics-whiz
author_rank: Regular Contributor
timestamp: June 22, 2015, 11:58:39 pm
content: I have an old VFD type device that has six of these units. It did work, one day something in it popped and it died. Visual/smell test lead nowhere.The device has a rectified DC supply in it which feeds to the drive circuit that has 6 MJ10000 transistors on small heatsinks.The issue was that once you tried to apply output power the small internal breaker/switch would trip. I removed the DC supply to the transistors and the issue stopped. This leads me to think one or more transistors failed.I'd like to test these transistors, but not sure what the best way would be besides maybe ohm test and I'm not sure what a reasonable value would be or proper polarity lead to transistor pin for testing.

author: dacman
author_rank: Frequent Contributor
timestamp: June 23, 2015, 01:40:03 am
content: That's a power Darlington with an internal diode and two internal resistors. I'd just test them individually (if I couldn’t test them in-circuit). There should be a difference if one or more is bad.From the emitter to collector, there is a protection diode. With high on the emitter and low on the collector a meter should read a forward diode junction. It should read open the other way around.From the base to the emitter, there are two base to emitter junctions, but there is also about 115 Ohms in parallel with that. It will read low both ways (unless testing with high current, which I don’t think is necessary).From the base to the collector, the path goes through the base to collector junction of the first transistor, but there is also the two resistors and protection diode that are in parallel with it. There should be a reading forward and it should be open reversed.Again, I’d compare the readings to a known good one.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: June 23, 2015, 01:42:36 am
content: I just used these directions to try and test them.http://www.ehow.com/how_8046802_test-darlington-transistors.htmlAt least using these in the diode test mode all 6 of them seem to be toast.3 seem to test fine until do the reverse bias they fail that. The other 3 fail the normal test and pass reverse bias. To me, this shows either these directions are not the best or the small pop I heard was in fact all 6 of these failing at once.0Based on some failing reverse bias it seems possible it may have damaged the small transistors and/or optoisolators driving these although there is a diode between the base and the driver parts on each.What do you think of my test results and chances of more extensive damage from these failing?I removed them from the circuit for testing and I doubt I have anything this same model to compare.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: June 23, 2015, 02:04:29 am
content: I just tested them with the way was mentioned in the posting on the forum. 3 fail at test 1, all 6 seem same with step 2, the other 3 fail at step 3.It appears all 6 of them are fried even though it failed I was only trying to run a single phase 120V motor. The unit was made for 208, was told 110 or 240 would also work.Not sure if I should replace them and hope for best or just junk the thing since I have a better AB PLC unit to tinker with. It seems the other parts ceramic caps, base diode, resistors, etc all check out okay so seems may be fine with new transistors.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: June 23, 2015, 02:13:42 am
content: Just looking into prices for these units element 14 seems to be cheapest at $6.90 each which would be like $45 to change all 6. Seeing these are rated for 20A 450V these failing just don't make since when unit has like 2A breaker and was a small one phase motor. Seems has to be another reason it failed.I don't think I'll be fixing this thing although nice to know I did decent finding issue finally.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: June 23, 2015, 03:57:11 am
content: I have probably like a few hundred of these they say is suitable for motor use, I got from SMPS.http://www.datasheet-pdf.com/datasheet/ToshibaSemiconductor/824928/K2915.pdf.htmlI know not exat same part bus seems you could replace a Darlington transistor with another type and maybe some extra bits and pieces.