speedball transistor question

[crappyjones123]

I was working on the speedball kit and mistakenly soldered the the 2x 2N2222A transistors too close to the pcb - one is barely off the board and the other is sitting flush against it. in my continuous efforts to desolder them to create some gap as suggested in the manual, i am afraid i might have damaged the transistor. they look the same as when i installed them but i dont know if they have suffered any thermal damage that is not visible.

suggestions are welcome .

i have the amp running stock right now with the exception of a pair of sprague electrolytic 470uf 200v caps for the output caps. very nice amp to say the least.

 

[HF9]

Transistors can usually tolerate a decent amount of heat, but if you feel you damaged them, why not order another set? They are less than $1 each on Mouser.

 

[JC]

I would like to think that even Radio Shack still has these, too.  Most likely not as cheap as mail-order, but I guess you pay for the convenience of picking them up rather than waiting...

 

[grufti]

It should be safe to just give the boards a try, that is to say: I looked at the circuit and can't find a reason why a damaged transistor would cause any grief other than simply not allowing the circuit to work.

I could be wrong though.

 

[crappyjones123]

Check the resistance of the base to collector, swap leads and measure the same two leads.  One way you get a diode forward biased, low resistance, and the other almost infinite resistance.  Then check base to emitter.  The same thing should happen.

If this checks out the transistor is probably good.

Note: This doesn't work on all meters, but most.

I have no clue what any of that means or how to do it.

Any words from the designers regarding continuing or switching out the transistors?

 

[JC]

Probably your biggest concern would be if you somehow shorted a transistor.  If your DMM has a diode check feature, use this.  Otherwise, something in the 2000 Ohms range may do it.

On your schematic, the transistor will be a circle with three leads going in.  Usually, the lead that is perpendicular to the straight bar or line is the base.  The lead with an arrow on it is the emitter.  That leaves the collector as the last lead.  Hopefully, you will have high resistance between emitter and collector.  The other checks are as Grainger has described.  Besides differences in meters, the associated circuitry can make this test dicey sometimes, but if you see anything approaching zero or very low Ohms, it is probably worth pulling the transistor. 

Usually small signal transistors of that sort can sit on the PC board without much trouble, provided they're not being run in such a way as to be dissipating a lot of heat.  While it is generally better to mount them in such a way as to be able to see some light between them and the board, you may well be OK.

As you say, a designer will be able to tell you for sure.

 

[Doc B]

Any words from the designers regarding continuing or switching out the transistors?

Plug the sucker in and try it!

 

[crappyjones123]

Any words from the designers regarding continuing or switching out the transistors?

Plug the sucker in and try it!

good enough for me. will finish the rest of the speedball kit and try it out tomorrow.

thanks for all the help guys.

 

[crappyjones123]

i ended up finding a few of these transistors in the EE lab upstairs at my university. However they are marked CEN 2N2222A with M0428 written underneath it.

just wanted to make sure that there arent any issues with this particular brand or if i shouldnt be using it at all.

 

[Doc B]

As long as they say 2N2222A they should be good to go.

 

[Yoga Flame]

I am in a similar situation, having over-enthusiastically soldered the transistors flush with the board and clipping the leads before scrolling down on the PDF to find the next paragraph's "leave some space" instructions.

Is the space meant for heat dissipation? Will I be able to get away with leaving the transistors as they are now? Or what if I attach heat sinks onto them? (http://parts.digikey.com/1/parts/988284-heat-sink-18-1w-blk-322400b00000g.html)


But give it to me straight... if I gotta desolder them then I gotta desolder them.



[edit: fixed wrong link]

 

[Doc B]

Should be OK, with the solder mask keeping any traces from shorting to the case.