How to best fix capacitor mistake?

[Neuronal]

Hi all - I am almost done with my SEX amp build, and when I reached to install the 47 microfarad 450V capacitors I realized that I had mistakenly installed one of them between terminals 24 and 29 (where I should have put a 250V 220uF capacitor). I have tried to use a soldering iron and braid to remove the incorrectly installed 47uF capacitor, but because those particular terminals are so tightly packed I can't seem to get it out. What is the best course of action at this point? I am inclined to cut off the leads of the capacitor at its base and then a> try and get the residual bits of the leads out of the terminal using braid and the soldering iron and b>call and beg the Queen to sell me a replacement 47uF capacitor. Does anyone have any better ideas - it is definitely frustrating to have gotten this far only to have made a totally rookie error! Also if I can't get the old bits of lead out of the terminal (and therefore there is no hole for me to insert the 220uF capacitor), is there a way for me to attach the capacitor somehow to the top of the terminal?

Thanks in advance for your advice -
Bob D.

 

[JC]

In your attempts, have the leads ever come loose?

In such a case, I generally try to get the lead loose before attempting to remove the solder.  In other words, get the part out first, then work on getting enough solder out of the way to install the replacement.

I know it may seem counter-intuitive, but you may have to actually re-solder the joint first to insure that all the solder in the joint liquifies, then when it does, pull out the lead with your needle-nose pliers.  Repeat with the other lead.  If you can get one lead out, the second one usually becomes easier to remove since the body of the part is half-loose.  Then, once you've got the part out, go to work on removing solder from the joints so you can get the replacement part in. 

I have been known to use a pointy metal object to just poke a hole in the heated solder in order to accomplish this, but if you try this you will want to keep it moving.  Otherwise, you may end up soldering the tool in place!

BTW, good for you for catching your error before it became a head-scratcher when you tried to run the amp!

 

[Grainger49]

This is not a clean way to do things but you could clip the cap leads as flush as possible to the terminals.  

If you need to extend the leads then solder on wire and use them.  

It is dirty but it works.  If you clip flush you won't inject noise where you removed the caps.

 

[Neuronal]

Thanks to both of you for your advice. I think I am going to take a shot at trying JCs approach before clipping the capacitor lead. One last question - there is a resistor wired in parallel to the same two terminals as the capacitor, and there is a diode going into one of those terminals - it is likely that I am going to fry those components when I reheat the joint? What should I do to avoid that?

thanks again - Bob D.

 

[ssssly]

Bend the two opposing terminal strips away from each other so that they are putting tension on the capacitor. Then grab the terminal stip with a needle nose plyer with one hand and heat the joint, from the opposite side as the capacitor. Once the solder begins to flow twist the terminal strip slowly while maintaining heat on the flowing solder.

If you grab the strip in the middle and rotate it you will have more luck than trying to pull it forward or back. Should get the cap out of there without destroying it.

 

[JC]

it is likely that I am going to fry those components when I reheat the joint? What should I do to avoid that?

Well, hopefully, you won't have to apply heat to either joint much longer than you did when you originally soldered it.  Of the two, though, I would imagine that the diode is the one to be concerned with.  If you have one of the little clip-on heat sinks, you could use it near the diode body.  If you don't have one, you can conjure one up with a spare set of needle-nose pliers and a heavy rubber band around the grips to keep them closed.

Just don't leave the soldering iron on the joint for extended periods of time.  If you are having trouble with a lead, back off for awhile to let everything cool a bit while you re-think your approach.

BTW, sometimes an extra hand, even a non-technical one, can come in very handy.

Good Luck!

 

[Neuronal]

So I managed to get the capacitor out without clipping the leads, and I noticed that there was some heat damage to the 270 kOhm resistor that sits in parallel with the capacitor (the paint chipped off one side - I can see the silver underneath) and is also wired between terminals 24 and 29. I measured the resistance at the terminals, and they are the same on both sides - about 550 ohms between terminals 24 and 29, and about 550 Ohms in the equivalent part of the circuit on the other side, between terminals 9 and 4. Am I good to go (meaning is the damage just cosmetic?), or should I replace that 270 kOhm resistor?

Thanks so much again - I appreciate it...
Bob D.

 

[JC]

Boy, as long as you're in there, I think you might as well replace anything that shows signs of physical stress.  That resistor may very well be perfectly OK, or it may fail when it is asked to perform at full power.  Or, it may last a month or forever.  The problem is, there really is only one way to find out:  Finish the amp and turn it on. 

The issue, it seems to me, then becomes:  Will it be easier to replace it now, or after the rest of the parts are installed?  If the answer is "Now", then I think I would contact Eileen for a replacement .  For peace of mind, if no other reason.

 

[Maxwell_E]

Looking at my SEX, I can see that resistor would be rather difficult to remove once you put the capacitor back in. The terminal strips are actually bent away from each other to squeeze it in there. If it were me and I had any doubts, I'd replace it now before you button it all back up.

 

[Neuronal]

Thanks guys - I am definitely in the better safe than sorry camp, so I've emailed the Queen for a replacement. Thanks again for all the advice -
Bob D.