开云体育

Before I jump into replacing the low voltage power supply filter capacitors I wanted to see what technique others have used. My concern is damaging the circuit board. What is the best way to remove the solder while avoiding damaging the circuit board?
Thank you,
Bill

I have successfully changed all the caps in one of mine, a a few other as well.
I used a fairly powerful iron with a broad and thick tip. That will melt the solder very quickly, especially if you add some in the process for better heat conductivity. Suck the solder one pad at a time. When all the pads are done, reheat them a bit, one at a time, and slightly wiggle the cap from underneath. Do that very gently; some pads are also connected on the other side. If you don’t suck all the solder, you risk breaking the pad when pulling the cap. Remember to check all the connections on the other side of the board too.

Hope that helps.

I've never had any problems but I have a Metcal setup. Suitable high end equipment (Pace, Metcal, etc) always helps.

Chipquick might be a good way to lower the melting point on those joints and minimize damage to the board.

And of course, use the little adapter boards to mate the modern snap cap to the 4 pin layout for the NLA original caps.

Paul

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

In case you haven't already come across these things:

Here's the adapters Paul is referring to:

eBay listing number "273254508468".



Seller is:



Or search for "Capacitor Adapter 15.5mm triangle".

Worth reading:

/g/TekScopes/files/Tek%20465%20Power%20supply%20Capacitor%20Replacement%20Guide%20-from%20web-/_Tek%20465%20Power%20Supply%20Capacitor%20Replacement%20Guide.pdf

Note that's from this groups files section. Search for "465 Power Supply Capacitor" to find it and others.

A message on this board where I describe the caps I selected to order from Mouser: /g/TekScopes/message/176235

If you go back to the beginning of that thread there's a link to a photo album showing a problem I encountered: /g/TekScopes/album?id=258720

The little trace circled in red in one picture shows the little jumper trace on the backside of A9 coming from C1512. It was the trace via from the front side to the back side that pulled out with the cap body when removing it. It didn't so much as pull out as disintegrate in tiny pieces that I didn't realize where there. I didn't find the problem until it was all reassembled and this little route wasn't reconnected. The solder wouldn't flow from the front to rear through the via without the trace material there. It was a bear to get fixed. Cautionary tail: continuity check all vias before reassembly. Repair damaged ones with copper tape. Available in mass quantities on Amazon.

Good luck and enjoy! It's very satisfying to recover a scope that's in good physical condition.

Dave

Hi Bill,

I slip a single ended hacksaw blade just under the cap, and saw off the lugs to remove the cap.? After that, very little heat is needed to remove the nubs from the board.

Make sure you do not leave any filings behind.

Good luck !

--
===============================
Scott Singelyn
Information Systems Manager
Flat Rock Metal, Inc.
26601 W. Huron River Dr.
Flat Rock, MI 48134-1090
Phone: (734) 782-4454 x 2660
Fax: (734) 782-5640
===============================

On Tue, Apr 27, 2021 at 09:45 AM, Dave Peterson wrote:

In case you haven't already come across these things:

Here's the adapters Paul is referring to:

eBay listing number "273254508468".

I have used this seller's products for years. They are excellent. Also note that he has added a larger via to allow the use of "snap in" capacitors. This opens up another group of capacitors for your projects. His previous design used 3 small vias for + and - sides, those vias would only fit "standard" wire leads, snap in cap terminals would not fit. With the addition of the larger via ion the group, you can easily use snap in caps.

--
Michael Lynch
Dardanelle, AR

Thanks everyone!! Doesn’t look so formidable a job now.

Bill

I agree with Stephen. Use enough iron! If you use too small of an iron
you'll have to hold it on the board for too long while you wait for the
solder to heat up enough and melt and there's a good chance that you'll
overheat the board and cause the copper traces to lift. Also get a
temperature controlled soldering iron if you don't already have one. I
guarantee that it will make a marked improvement in your soldering
ability. And with a temperature controlled iron you almost can't use too
large of a soldering iron! If it fits, it will work!

Before you start make sure that the iron, the solder and the joint are
all as clean as possible! I use Kester 2% silver solder and it has a very
low melting point, 300F or so. It mixes with the original solder and lowers
the melting point so that I can quickly unsolder the joint and avoid any
chance of overheating the circuit board or the part. For unsoldering
something I set the iron at about 650 F and melt some of the solder onto
the tip of the soldering iron then apply the tip to the joint on the
non-component side of the circuit board. I already have my manual solder
sucker cleaned, cocked and ready to go. Once the solder on the joint is
thoroughly melted, not just the top melted, I use the solder sucker to pull
up the molten solder. If done correctly you shouldn't have to hold the iron
on the joint for perhaps two to three seconds and it will remove all of the
solder from the joint except for perhaps a very slight amount directly
between the lead and plated hole. I then use a small flat blade screwdriver
to push the lead sideways in the hole and break the lead free from the
plating if it's still attached. If I did the previous step correctly then
the lead is usually already completely free. It should take only a small
amount of force to break the lead free, don't force it. If it won't come
free then there's probably still solder on the reverse side of the board.
Only after I've checked and made sure that all of the leads on the part are
free do I lift the part away from the board. It should come free with no
force whatsoever. On double sided boards after you use the solder sucker,
you need to look at the reverse side and be sure that the solder there was
melted and removed as well. If it's not then you probably didn't wait long
enough after the solder started to melt to allow ALL of the solder (on both
sides of the board) to melt. If that's the case then you need to resolder
the joint and then desolder it all over again. I've never found any other
reasonable method of getting all of the solder off of the component side
other than resoldering and starting over again. I developed this method
while repairing circuit boards that could NOT be replaced at any cost and
that not damaging the boards was absolutely the top priority. Once I worked
out all of the materials and techniques it worked extremely well and I've
repaired thousands of boards using this method. FYI I've tried vacuum
operated solder suckers such as Pace brand but I still prefer one of the
manual ones. It's just easier to use even if I do have to manually cock it
each time. Keep the tip clean and pull the tip off every so often and clean
out the old solder inside of the sucker and regrease the piston and they'll
work on and on and on. I've acquired a few more of them as spares but I'm
still using one that I bought back in the 1970s. If it's operating
correctly, you can cock one then put your finger over to tip and then fire
it and the piston will back back part way but not all of the way due to the
vacuum inside of it and it will *hold* the vacuum.
I probably have or or have had at least one of every brand of soldering
iron out there and a wide variety of Pace and other soldering and
desoldering stations but I do most of my work using a regular Weller or
Hakko (929 IIRC) temperature controlled soldering iron and an antistatic
version of the Soldapullt solder sucker. I've also used the metal Paladin
solder suckers but for anything larger than a small joint I like the
Soldpullt because it's slightly larger and pulls more air. BUT, it's very
important IMO that you use a *top* quality solder such as Kester even when
unsoldering a joint. The Kester 2% silver loaded solder is hard to find and
is now stupidly expensive but it's by far the best solder that I've ever
used and I HOARD every bit of it that I can find and I use it very
sparingly. I won't waste my time trying to use lead free solder. FOR
ANYTHING!

I started out soldering, *and desoldering,* with a 200 Watt American
Beauty soldering iron with no temperature control. You should try that
sometime! I delaminated a lot of circuit cards!

Bill (?)- wrote on 4/27/2021 12:40 PM:

I agree with Stephen. Use enough iron!

<much good information omitted>

Hello--

Under no circumstances should you use compressed air to
clear the molten solder from printed-circuit boards. Chaos ensues.

73--

Brad? AA1IP

I second Brad's warning. Compressed air is a Very Bad Idea(tm) here.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

The PACE solder rework training has some interesting "methods" for component removal



of course they only mention "Heat and Shake" but don't recommend it.

-- Jeff Dutky

I hate to admit it here but I have used a very hot hot air gun to heat
the backside of circuit cards until the solder melts and then slam the
board down on a table to knock dozens of surface mount components off all
at the same time. If the air is HOT and you don't have to heat the board
for more than about 20 seconds, the components survive surprisingly well.
But they usually scatter all over the place! You definitely don't want to
do it in a room with a carpeted floor!

I will definitely take my time and not damage the circuit board. I’ve always known to use sufficient heat and be quick about time on the board.

Great information from all!!

Thank you,
Bill

Someone stated:

… "it's very important IMO that you use a *top* quality solder such as Kester even when unsoldering a joint. The Kester 2% silver loaded solder is hard to find and is now stupidly expensive but it's by far the best solder that I've ever used and I HOARD every bit of it that I can find and I use it very sparingly. I won't waste my time trying to use lead free solder. FOR ANYTHING!"


I agree, I have used many resin cored solders (60/40, 63/37, 2% Ag, 4% Ag, Alpha brand, Kester brand, No-name, etc.) over the past 50+ years, and in terms of rosin smell (some I just could not stand!) and ease of use, I prefer the 4% Ag from Kester.


Around 15 years +/- ago, I bought as much of the 4% silver solder as I could afford, the .015" diameter Kester 4% silver, leaded solder, mostly, in my opinion, the finest that I ever used. It truly makes beautiful joints, using any soldering iron (for over twenty years I used a “tip" oriented temperature controlled Weller WP-60-3) until I bought several of the stand alone Weller and JBC station/iron units. I happen to sell an occasional item on eBay, almost 20% of the time, its the: 12’, 25’, 50’, 100’, and 200’ lengths of that .015 diameter, 4% silver, leaded Kester Solder.


Sorry for the self-aggrandizing mention, but that solder is still available, and some 2% Ag also (until I get down to my last roll).



Steven ( stevenel57 on eBay )

The cap cans themselves complete part of the circuits. What I'd do is to get the same value caps that will fit inside the empty cans (or on the bases). The cans can be cut open with a tubing cutter, or just by spreading the crimp at the bottom, then pulling the guts out. And yes you need a good dose of heat to melt the solder. Suck/wick out as much as you can, then go around and heat the tabs individually and work them out by wiggling a little as you go around with the iron.

I bought a vacuum pump desoldering station a few years ago. Works great -- doesn't overheat traces, gets rid of the solder, leaves an empty hole and a clean carpet:

Thanks for this. I'm still in the process of tooling up my workspace. This sort of input helps. There's a lot of sellers and a lot of cheap crap out there. A word of mouth promotion trumps a lot of sales pitch for me. I could easily break the bank trying to buy everything at once, so keeping cost down is a big deal. Looks like recapping power supplies is going to become a common activity on my bench! A robust extraction system is going to be very useful.

I've always loathed the plastic push-button type solder suckers. This looks like a nice setup. Clearly you're happy with it. I'll have to add it to the queue.

Dave

I've used Ungar, Hakko (both wand and gun), and Metcal.

I've found the Metcal system to be better, although you do have to make sure (for any of them) that the tip is clean and capable of good heat transfer.

One thing you can do is to use a larger (still controlled!) iron to heat an area, then use the solder sucking tip to vacuum up the solder.

There's only so much heat you can get out of something designed to *not* damage a delicate PC board, when the object needed an industrial soldering iron to heat the surrounding acre of board and part, let alone chassis.

Harvey