Identify  damaged transistors. - Page 1
Forum section: electronics / repair

author: f114
author_rank: Newbie
timestamp: August 04, 2017, 12:14:12 pm
content: I have this card with two damaged transistors that can not be identified by numbering. Could anyone tell which transistors could replace them?

author: Ian.M
author_rank: Super Contributor
timestamp: August 04, 2017, 12:20:51 pm
content: The lower one almost certainly isn't a transistor - it has 6 legs and the silkscreen says U2, so its probably an I.C.Without knowing exactly what the board is, what it does, and maybe a fair bit of reverse engineering to find out how it works, you are S.O.L.

author: technogeeky
author_rank: Frequent Contributor
timestamp: August 04, 2017, 11:38:44 pm
content: I would hazard a guess from both the size and package of the bottom chip that it's a transient voltage suppressor (TVS) array. It also looks like there's been some high voltage damage to the nearby traces, to the TVS itself, more traces, possibly the large-package SMD resistor (102).If the remaining contacts of the supposed TVS chip read like... diodes in both directions, perhaps you could identify it as such. In any case, a TVS would make sense there.Identifying the transistor will probably be more difficult, but you could start by assuming that it's the same transistor as another one of the same package size on the board (it looks like there is one with markings16on the board to the right).Was this device in a situation where it could have been struck by lightning, or connected to something that was hit by lightning?

author: f114
author_rank: Newbie
timestamp: August 05, 2017, 02:28:45 am
content: The device has been damaged by lightening. The above damaged transistor only identifies an "A" in the encapsulation label.Technogeeky thanks for the info.

author: EPTech
author_rank: Regular Contributor
timestamp: August 06, 2017, 10:11:00 am
content: Hi There,Can you get any markings of the IC? It may as well be a 1-gate logic IC or a dual transistor or FET, hard to tell. The resistor under R9 seems to be damaged as well and the trace running from that one to the IC looks like it has been vaporized.Q5 may be a simple NPN transistor like a BC847. Check whether pin 2 in connected to GND after unsoldering Q5.Happy repairing.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 06, 2017, 01:57:52 pm
content: Everything in the circuit path of that IC has exploded, that little right angle trace below and to the IC (eww, bad layout), the trace to the resistor, the resistor itself, and the trace and via leading from the resistor. There could be more blown traces and components on the other side of that via, and hopefully it's only two layer.

author: f114
author_rank: Newbie
timestamp: August 06, 2017, 07:01:42 pm
content: OK. thank you for the informations

author: Ian.M
author_rank: Super Contributor
timestamp: August 06, 2017, 08:34:02 pm
content: The via between R9 and Q5 (by base of top arrow., bottom pic) looks suspicious. Its on the track that had the short segment to U2 vaporised.My professional opinion is its FUBARed - even if you had original new replacements for everything you can see that's visibly bad, and jumpered all the missing tracks and possibly damaged vias, you'll find further damage that will prevent it working properly and/or reliably.e.g there's a track with a 330R series resistor from the blown transistor Q5 to pin 15 of theHoltek HT66F004 MCUso that's probably suffered as well and replacements for obscure custom programmed parts like that usually have to be salvaged off an identical donor board.