Are these transistors damaged? - Page 1
Forum section: electronics / beginners

author: MiniCheck
author_rank: Contributor
timestamp: August 23, 2024, 09:48:45 pm
content: If you look at the transistors circled in the picture, there seems to be what looks like holes on top of the transistors. The T50 one is the worst one - the other one's seem to be ok but they have this circle pattern on top. The board seems to be working fine (part of a car's instrument panel), although I haven't fully checked it. The T50 is a BC32716. The T58 is either a BC217C or BC2317C - can't quite read the section digit. And the other one in front of it is a BC33740.Thanks for your help!

author: MathWizard
author_rank: Super Contributor
timestamp: August 24, 2024, 03:53:11 am
content: I hope it's not a virus, but after DLing and trying to open it, the win10 viewer said it's not supported or corrupted. ??

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 24, 2024, 04:49:16 am
content: I think that's just a plastic molding flaw.I managed to open the picture in Gimp and fix it:

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 24, 2024, 07:39:29 am
content: I also opened it in Gimp. and it does look like normal production "ugliness". Also note that both T38 and T70 have a weird small bump and both have it in exactly the same spot.With BJT's you can also measure both the base-emitter diode and the base-collector diode with a DMM. If both measure around 600mV then you can be pretty sure the transistors are OK.

author: MiniCheck
author_rank: Contributor
timestamp: August 25, 2024, 03:56:16 pm
content: Thanks for the responses. Apologies for the unreadable attachment. It was in Apple's HEIC format. I should have converted it to JPEG.As suggested, I checked the base-emitter diode and the base-collector diode which measured just under 700mV which looks pretty good.Appreciate the help!

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 25, 2024, 05:29:23 pm
content: Also measure between the emitter-collector leads and make sure that's not shorted. I've encountered that before. B-E & B-C will check out OK individually, but they are now in "parallel" because the E-C is shorted.

author: pienari
author_rank: Regular Contributor
timestamp: August 25, 2024, 05:38:52 pm
content: In right corner i can see capacitor and mayde it is leaking or water damage.. something.

author: MiniCheck
author_rank: Contributor
timestamp: August 25, 2024, 07:29:55 pm
content: Quote from: pienari on August 25, 2024, 05:38:52 pmYeah, I noticed that too. On close inspection it seems to be the same material that covers the screws. Not sure why it's there.

author: MiniCheck
author_rank: Contributor
timestamp: August 25, 2024, 07:41:46 pm
content: Quote from: Kim Christensen on August 25, 2024, 05:29:23 pmI just picked one of the transistors and I got around 674mV when measuring across C (+) and E (-) but OL when the leads are the other way round i.e. C (-) and E (+). Does that sound about right? That's with the DMM in diode mode.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 25, 2024, 07:56:19 pm
content: Yup... Sounds about right.In circuit diode checks of PN junctions need to be taken with a grain of salt, because other components can make it look bad when it's not. Or make it look good when it's bad. Plus, it doesn't tell you if the transistor has really low beta.ie: Some resistors on their own will measure around 700mV on diode check. A low value resistor across a PN junction can make it look shorted when it's OK. etc.