Problem with U3

[allstar]

Hi everybody, I thought I would give this board a try for my problem. I am working on an almost completed A12.
http://www.allstarstudios.net/images/preamp/A12_Mic_Preamp_008.jpg

Everything was going just great on my A12 until I got to installing the IC regulator U3. I soldered it on backwards without realizing it, and then I had a heck of a time getting it off. The part was subjected to a lot of heat and physical stress from my pliers- I'm pretty decent at soldering but I'm totally new to *un*soldering. So, my first question is: What exactly is an IC Regulator, and how robust is this component? Do I need to buy a new one, or is the one I have probably still alright? Is there a way to test it? And if I have to buy a new one, where do I get it (preferrably quickly).

Here are some pictures of the stressed component:
http://www.allstarstudios.net/images/preamp/A12_Mic_Preamp_013.jpg
http://www.allstarstudios.net/images/preamp/A12_Mic_Preamp_014.jpg
I don't know if these photos provide enough detail to really evaluate the condition of the component. I should also note I was tugging on the piece and heating the leads to get it off the board with the heat sink already removed.

My other problem is slightly worse. Although warned about this throughout various portions of this website, by harrasing the component to try to get it out I caused one of the circuit board pads to peel up on the backside:
http://www.allstarstudios.net/images/preamp/A12_Mic_Preamp_010.jpg
How do I go about fixing this?

Thanks in advance for any help, comments, or suggestions!

[tpryan]

If I had to bet, I'd say the regulator is still OK. They're really fairly hard to kill. There's no easy way to test it without putting it back in a circuit, though, so you may want to save yourself the possible trauma of removing it a second time by getting a replacement. Radio Shack used to sell them, but if they don't any decent electronics shop should sell you one.

The board doesn't look too bad from what I can see, but even if you've actually lifted a pad it's not a total loss. First, clear the holes with solder wick. Use an X-Acto knife to scrape the solder mask from about 1/4" of the trace leading up to the damaged pad. Insert the new component and bend the lead over the exposed copper, then solder the lead to the trace. Be extra careful, since the trace is less rugged than the plated-through hole and pad.

In the future, keep in mind that the PCB is by far the most valuable component, especially after having stuffed most of it. If you're having trouble removing a part, it's almost always better to sacrifice the component to avoid damaging the board. Simply snip the leads and remove them one at a time, then clear the holes with solder wick.

[Category 5]

Radio Shack stocks both 337s and 317s. I would use a new part just to be safe.

For miffed traces you could try that copper PCB tape. I got some for doing generic cicuits on blak boards and it works pretty well. It dawns on me that the stuff is more suited to repairs than whole designs. You can get it here

http://www.acme-sales.net/acmecart/html ... ortal.html

Shane

[allstar]

Thanks guys! It looks like I should be able to somehow get the component lead soldered to the trace, so I probably won't need to do any PCB retracing.

Concerning replacing the part, I am a little confused what to look for at Radio Shack or any other electronics store. Is this piece (the 337) a transistor, just a heatsink, or something else entirely? What kind of tolerances am I looking for when I replace it (i.e how critical is it that it matches the 317, since they are on oppsing sides of the power circuit, as best I can tell)? Cat5 do you know the radio-shack part # for a 337?

Thanks again!

[tpryan]

LM337T, negative linear adjustable voltage regulator. They're made by several companies, any will work, but I prefer the National Semiconductor parts.

[Category 5]

They are easy to find at Radio Shack. Even though they are all packaged the same you will find different mfgr. parts in each package. You will probably be able to find the National Semiconductor part Tim prefers if you look at a few.

Radio Shack must just buy up bulk surplus lots and sort them by component number.

Shane

Tim,

Radio Shack doesn't have them, but do you know where I can find some of those 2 lead jumper pins aside from DigiKey? I need a pair of them for a Digital Readout project I did for my Dad's milling machine. The sooner I get the readout to him the sooner he'll start machining my G7 mic parts!

Shane

[tpryan]

Do you mean the headers (the pins) or the jumpers? The shorting jumpers are used all over PC motherboards and disk drives, so you should be able to find them easily. The headers are usually sold in long strips, and you just snap off what you need. They're standard 0.1" spacing. Most electronics shops I've been in carry them, though I don't know if Radio Shack does any longer.