solder wicking up legs of 2N2907A -- test for bridged solder?

maryc27182 · 1679

0 Members and 1 Guest are viewing this topic.

Offline maryc27182

  • Full Member
  • ***
    • Posts: 88
Hi folks, how are you? I'm building the shunt regulator PC board, and just finished populating/soldering. I realized after soldering that I can't quite see underneath the 2N2907As, and of course, a little solder has wicked up the legs to the underside of the cans.

I don't think there is bridging between the legs, and it's definitely not bridging to the can itself. However, it's really hard for me to tell if there might be bridging between the legs, so I was looking for a test.

I found this: http://bottlehead.com/smf/index.php?topic=1478.msg10639#msg10639
 and checked resistances between the legs. I basically get what my meter thinks is infinity--no where near the 770 ohms that this previous post said was OK but also nowhere near the 3.5 and 11.5 ohms readings that he called "low" (but that was for the Seductor, and I don't really understand what I'm measuring, to be honest, being an aero/mech engineer, and only having decent understanding of the most basic electrical and electronic stuff.)

I know I should just pull up the transistors and check, but I'd rather not unless that's the only option. If anyone knows, let me know, thanks. And of course, I can pull these off and look, but obviously I've spent way more time looking online and typing this up hahaha.

Mary

DIY 2-ways (TAD TD-2002, AE TD15M), Stereomour 45
Fostex TH-500RP, S.E.X. 2.1
Eros Phono


Offline Doc B.

  • Administrator
  • Hero Member
  • *****
    • Posts: 9657
    • Bottlehead
Reply #1 on: November 16, 2016, 08:37:48 AM
Assuming that you are getting good contact with the test lead tips, if you see an infinite reading between the pairs of legs you are good to go.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline maryc27182

  • Full Member
  • ***
    • Posts: 88
Reply #2 on: November 16, 2016, 08:47:42 AM
Thank you! I think I got good contact with my leads, plus I found my brightest LED headlamp and got that shining underneath the transistor--I think I'm OK. Thank you, though, for taking the time to reply.

I also did a more thorough google check to try to understand what I'm measuring--and of course, found nice basic explanations. For those interested, here's one: http://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/meter-check-transistor-bjt/

Mary

DIY 2-ways (TAD TD-2002, AE TD15M), Stereomour 45
Fostex TH-500RP, S.E.X. 2.1
Eros Phono