7 May
2011
7 May
'11
9:04 a.m.
I need to desolder a chopper transistor from a PCB in the PSU of my PDP11 so
that I can test it and if necessary replace it. The trouble is that I am not
experienced with soldering and desoldering and I am having a lot of trouble
desoldering it. I have made several attempts, damaging one of the PCB tracks
in the process (should be repairable by adding a wire). I have a cheap
Weller 40W soldering iron and I have been using some narrow tips. I have one
of those pumps for sucking out the molten solder. I also have 2mm solder
wick (braid?).
I seem to have removed most of the solder from two of the pins, mostly with
the pump, the solder wick just does not seem to pick up any solder not
matter what I do. One of the pins, however, goes onto a track that is more
like a large area of metal and the iron does not even seem to melt the
solder there.
The thing I really don't understand is how you desolder more than one pin at
the same time. There is always bound to be just a little solder left holding
each pin in place no matter how much you remove with the pump or wick. So
it seems to me that you would need to have the solder in all 3 pin holes
molten, all at the same time, to be able to lift the component.
What is the trick? Or is it just that my soldering iron is not good
(powerful) enough?
Thanks
Rob
7 May
7 May
9:40 a.m.
On 07/05/2011 10:04, Rob Jarratt wrote:
I need to desolder a chopper transistor from a PCB in
the PSU of my PDP11 so
that I can test it and if necessary replace it. The trouble is that I am not
experienced with soldering and desoldering and I am having a lot of trouble
desoldering it. I have made several attempts, damaging one of the PCB tracks
in the process (should be repairable by adding a wire). I have a cheap
Weller 40W soldering iron and I have been using some narrow tips. I have one
of those pumps for sucking out the molten solder. I also have 2mm solder
wick (braid?).
You don't normally desolder more than one pin at a time but you do need
a good iron and a good pump. On DEC PSUs particularly, I've found the
holes are, um, less than generous -- the component pins tend to be a
close fit and there's not much room around the pin even when you get all
the solder out.
I normally use a 100W Weller soldering gun for things like those
trannies (I have a 50W Weller temperature-controlled iron for anything
else). The trick is to get the solder hot enough to flow, and to do so
quickly. If you can't do that, you're unlike to succeed, and the longer
you leave the heat on the pad, the more likely you are to damage
something. Then use a large pump to suck it off. Sometimes adding
fresh solder and trying a second time helps -- the first attempt removes
most of the oxidised stuff and the flux from the fresh solder helps
remove the last of it. Then push the pin from side to side to break the
last whisker of solder that bridges from the pad across the gap to the
pin -- if you can!
I'd suggest getting a bigger iron if you can, and don't use a narrow tip
for large components. I wouldn't waste any time on solder braid, either
-- fine for small stuff but probably not for this.
--
Pete Peter Turnbull
Network Manager
University of York
1:26 p.m.
Date: Sat, 7 May 2011 10:40:55 +0100
From: pete at dunnington.plus.com
To:
Subject: Re: Desoldering a chopper transistor
On 07/05/2011 10:04, Rob Jarratt wrote:
Hi
I thought I'd mention that you always need to refill with solder if it misses
getting it all out. Try heating both sides with two irons( tough with only
two hands but I've gotten good with holding the pump and iron at one
side with just the one hand. You need something to clamp the board.
Also, when first melting the solder, make sure the pin is free and
centered in the hole. I push the lead around with the iron and solder melted
until it feels right( it is a feel thing ).
It seems that no matter how well it is cleared, some small bridge seems
to be there. Often this can be easily broken loose with a little pressure
I need to desolder a chopper transistor from a
PCB in the PSU of my PDP11 so
that I can test it and if necessary replace it. The trouble is that I am not
experienced with soldering and desoldering and I am having a lot of trouble
desoldering it. I have made several attempts, damaging one of the PCB tracks
in the process (should be repairable by adding a wire). I have a cheap
Weller 40W soldering iron and I have been using some narrow tips. I have one
of those pumps for sucking out the molten solder. I also have 2mm solder
wick (braid?).
You don't normally desolder more than one pin at a time but you do need
a good iron and a good pump. On DEC PSUs particularly, I've found the
holes are, um, less than generous -- the component pins tend to be a
close fit and there's not much room around the pin even when you get all
the solder out.
I normally use a 100W Weller soldering gun for things like those
trannies (I have a 50W Weller temperature-controlled iron for anything
else). The trick is to get the solder hot enough to flow, and to do so
quickly. If you can't do that, you're unlike to succeed, and the longer
you leave the heat on the pad, the more likely you are to damage
something. Then use a large pump to suck it off. Sometimes adding
fresh solder and trying a second time helps -- the first attempt removes
most of the oxidised stuff and the flux from the fresh solder helps
remove the last of it. Then push the pin from side to side to break the
last whisker of solder that bridges from the pad across the gap to the
pin -- if you can! from a small screwdriver. If that doesn't work, I
put the iron on the
lead with sideways pressure. Just as the lead pops, I remove the
iron.
The idea is to heat it just enough to make the solder start to soften
but not so much as to melt it all and attach the lead someplace else.
If this fails, I refill the hole with solder and try to adjust the lead
again, while hot, to center it in the hole.
As a last resort, I go to a friend house that manufactures burn-in boards.
He has a solder pot. It is full and I just set the board on the brim
of solder. I then just pull the part out.
Do remember through all this, do not put pressure on the traces
with the iron. Use a clean iron well tinned iron. You can't clear
a partially cleared hole, you need to refill it and try again.
Use bottled flux if you can get some, it helps to keep the solder
surfaces fresh.
Also, although many like solder wick, I'd done more damage with
it then I'd like. I now only use the pump( not the small one with the
yellow lever on the side. It is junk.The larger the better ).
Dwight
I'd suggest getting a bigger iron if you can, and don't use a narrow tip
for large components. I wouldn't waste any time on solder braid, either
-- fine for small stuff but probably not for this.
--
Pete Peter Turnbull
Network Manager
University of York
4:14 p.m.
Pete Turnbull wrote:
On 07/05/2011 10:04, Rob Jarratt wrote:
Also, once you have most of the solder removed from the feed through
hole then you can push on the leg of the device with a small screwdriver
(or the like) to try to release it from the side of the hole. Most
device legs go in the hole on an angle, thus there is a tiny film of
solder holding the leg to the side of the hole - sometimes on both the
top and the bottom of the hole. You will feel or hear a tiny 'click' as
the leg releases.
Looks like this (somewhat crappy ASCII sketch)
\
|\ | <--- Top of feed through hole
| \ |
| \ |
| \| <--- Bottom of feed through hole
\ <--- Leg of device
So you are trying to break the top and bottom points by pushing the leg
away from the side of the hole it is soldered to.
If done correctly the device will then be easy to remove with only
finger force - no prying with the screwdriver!
Hope that makes sense!
John :-#)#
--
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
www.flippers.com
"Old pinballers never die, they just flip out"
I need to desolder a chopper transistor from a
PCB in the PSU of my
PDP11 so
that I can test it and if necessary replace it. The trouble is that I
am not
experienced with soldering and desoldering and I am having a lot of
trouble
desoldering it. I have made several attempts, damaging one of the PCB
tracks
in the process (should be repairable by adding a wire). I have a cheap
Weller 40W soldering iron and I have been using some narrow tips. I
have one
of those pumps for sucking out the molten solder. I also have 2mm solder
wick (braid?).
You don't normally desolder more than one pin at a time but you do
need a good iron and a good pump. On DEC PSUs particularly, I've
found the holes are, um, less than generous -- the component pins tend
to be a close fit and there's not much room around the pin even when
you get all the solder out.
I normally use a 100W Weller soldering gun for things like those
trannies (I have a 50W Weller temperature-controlled iron for anything
else). The trick is to get the solder hot enough to flow, and to do
so quickly. If you can't do that, you're unlike to succeed, and the
longer you leave the heat on the pad, the more likely you are to
damage something. Then use a large pump to suck it off. Sometimes
adding fresh solder and trying a second time helps -- the first
attempt removes most of the oxidised stuff and the flux from the fresh
solder helps remove the last of it. Then push the pin from side to
side to break the last whisker of solder that bridges from the pad
across the gap to the pin -- if you can!
I'd suggest getting a bigger iron if you can, and don't use a narrow
tip for large components. I wouldn't waste any time on solder braid,
either -- fine for small stuff but probably not for this.
9 May
9 May
7 p.m.
Also, once you have most of the solder removed from
the feed through
hole then you can push on the leg of the device with a small screwdriver
Sometimes fine-nosed pliers are a more suitable tool.
(or the like) to try to release it from the side of
the hole. Most
device legs go in the hole on an angle, thus there is a tiny film of
solder holding the leg to the side of the hole - sometimes on both the
top and the bottom of the hole. You will feel or hear a tiny 'click' as
the leg releases.
Looks like this (somewhat crappy ASCII sketch)
\
|\ | <--- Top of feed through hole
| \ |
| \ |
| \| <--- Bottom of feed through hole
\ <--- Leg of device
So you are trying to break the top and bottom points by pushing the leg
away from the side of the hole it is soldered to.
This works well fro removing DIP ICs and the like. After using the solder
sucker and freeing the pins on the sodler side, you then put a small
screwdriver blade on the component side of the board so that it presses
on the ICB pin close rioght on the PCB. Then push the pin inwards,
towards the body of the IC. As you said, you'll feel it 'give. After
freeing all the pins, the IC should lift out with no problems.
Another tirck which I hesitate to metnion for components with pins in a
line, like SIL resisotr packs is, after desoldering nad freeing the pins
as a bove, if it still won't come free, rock it carefully at right angles
ot the line of pins. You can then see whick pinsare moving (and are thus
free, and which need to be resoldered and desoldered again to free them.
If done correctly the device will then be easy to
remove with only
finger force - no prying with the screwdriver!
IMHO much of the skill in removing components is to know how much force
you can apply without damaging either the PCB or the component. You can
try carefully prising it up with a screwdriver, but if it doesn't come
easily, don't apply more force or you will either crack the component or
rip traces off the PCB. Stop and find out what's holding it..
-tony
8:07 p.m.
Hi
My problem with solder wicks is that if it is working well,
it pulls all the solder up the wick, including any that was
on the iron and I no longer have good heat conduction.
This tends to leave the wick attached to the board and
I often end up lifting traces.
I haven't lifted any traces with my sucker in many years.
( not to say I never did, just not for quite some time ).
Dwight
7 May
7 May
1:40 p.m.
A few points
1. If the device is dead, or cheap, just cut it off above the board,
the board is rare/delicate the device commodity and replaceable, then
each leg can be got out above board, even the solder sucking process
can do this for you. least board heating
2. after sucking all three, I try to jiggle each lead to check its
free/break any small amount of solder left, hole has to be reasonable
clear
3. with a large iron add solder to get a blob on all three, pull
device out and then suck holes after
4. similar to above but rapid sliding of iron over the pins to get all
melted, then pull device
5. back in the old days there were iron tips around for multi pin
melting, I never found them to be too good
braid never worked that well for me
Dave Caroline
3:33 p.m.
On 7 May 2011 at 10:04, Rob Jarratt wrote:
The thing I really don't understand is how you
desolder more than one
pin at the same time. There is always bound to be just a little solder
left holding each pin in place no matter how much you remove with the
pump or wick. So it seems to me that you would need to have the
solder in all 3 pin holes molten, all at the same time, to be able to
lift the component.
What is the trick? Or is it just that my soldering iron is not good
(powerful) enough?
If you're going to do much repair of PCBs, a temperature-controlled
iron is pretty important. I use my venerable Weller TCP iron--a time-
proven design that's still in production after, what, a half-century?
However, there are less-expensive imported options.
A clean and well-tinned iron is vital to this kind of work. If your
iron isn't tinned, the molten solder can't conduct heat to the joint
and you end up spending too much time trying to get a joint to melt.
If you're using a solder pump, make sure it's the big one; the little
ones don't seem to be worth much. It often helps to add solder to a
joint before you use the pump to suck the solder out.
Once you've sucked the solder out of a joint (you should be able to
see daylight through the joint), wiggle the component gently to break
the bond between the lead and the PCB trace formed by any remaining
solder film and it should pop right out.
Others have suggested cutting the component body off the leads to
reduce heat conduction away from the joint being worked on--and
that's a very good suggestion.
If you still don't trust yourself, you may want to look into a low-
temperature solution, such as Chip-Quick, which is basically a low-
temperature fusible alloy that takes solder into solution. It's
quite valuable duing SMT rework (I have yet to damage a PCB using it
to replace surface mount ICs), but it might also work with
traditional through-hole devices.
http://www.chipquikinc.com/index.htm
I've got lots of desoldering braid, but I tend to use it for
soldering SMT packages, rather than desoldering them.
--Chuck
5:01 p.m.
I need to desolder a chopper transistor from a PCB in
the PSU of my
PDP11 so
that I can test it and if necessary replace it.
As you are just trying to isolate the device for testing, sometimes it
is easier to open the circuits elsewhere to achieve the isolation. For
example, if the collector goes to an offboard transformer through a
connector, then that lead is easily isolated; the base is probably fed
by a resistor and lifting one lead of the resistor will isolate the
base. With 2 of the 3 connections to the transistor open, it is
isolated for testing purposes.
TO-220 packages (3 leads with tab) can be very difficult to remove in
one piece when - as Pete was mentioning - the holes are to small. Some
manufacturers fail to increase the drill size for the wider TO-220
pins, they can be very tight with no room to wiggle the lead to break
the final solder bridge. Sometimes slightly twisting the lead might do
it. Sometimes you have to rock the device up and out of the holes with
several heating cycles.
5:58 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Brent Hilpert
Sent: 07 May 2011 18:02
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Desoldering a chopper transistor
easier
to
I need to desolder a chopper transistor from a
PCB in the PSU of my
PDP11 so
that I can test it and if necessary replace it.
As you are just trying to isolate the device for testing, sometimes it is open the circuits elsewhere to achieve the isolation.
For example, if the
collector goes to an offboard transformer through a connector, then that
lead
is easily isolated; the base is probably fed by a
resistor and lifting one
lead of
the resistor will isolate the base. With 2 of the 3
connections to the
transistor
open, it is isolated for testing purposes.
TO-220 packages (3 leads with tab) can be very difficult to remove in one
piece when - as Pete was mentioning - the holes are to small. Some
manufacturers fail to increase the drill size for the wider TO-220 pins,
they
can be very tight with no room to wiggle the lead to
break the final
solder
bridge. Sometimes slightly twisting the lead might do
it. Sometimes you
have
to rock the device up and out of the holes with
several heating cycles.
It is indeed a TO220 and I do need to test it. After sending my request I
had an idea and took the board to a local jeweller, he was able to remove it
for me by using a very fine drill to drill out the just the pins themselves.
The contacts look to be intact and even if they are not I will be able to
use wires to reconnect the transistor pins.
Thanks
Rob
8:10 p.m.
It is indeed a TO220 and I do need to test it. After sending my request I
had an idea and took the board to a local jeweller, he was able to remove it
for me by using a very fine drill to drill out the just the pins themselves.
Not generally as good idea! These PCBs have plated through holes, meaning
there is a metal layer o nthe insisde of the hole which connects traces
on both sides. If you drill out the hole you will damage this plating.
On a double-sided board you then have to solder the component leads to the
traces on both sides. On multilayer boards you have a long day ahead of
yuu.
-tony
11:55 p.m.
On 07/05/2011 18:58, Rob Jarratt wrote:
It is indeed a TO220 and I do need to test it.
Ah, that ought to be doable with a 40W iron. When I described using my
100W Weller, I was thinking of bigger stuff with metal cans!
After sending my request I
had an idea and took the board to a local jeweller, he was able to remove it
for me by using a very fine drill to drill out the just the pins themselves.
I hope those holes weren't plated-through ;-)
--
Pete Peter Turnbull
Network Manager
University of York
6:44 p.m.
I'd be tempted to suggest that you pick up some scrap boards from
somewhere (old TV/computer from the tip) and practise.
You want to non-destructively remove this component and you've already
lifted a track.
I'd stop now and practise on something that doesn't matter. Removing
something like
a 4 pin molex power connector from a dead (recent:-)) hard drive or
similar is
probably the sort of difficulty you want?
Antonio
arcarlini at iee.org
8:22 p.m.
I'd be tempted to suggest that you pick up some scrap boards from
somewhere (old TV/computer from the tip) and practise.
I owuld agree. The only way to learn to solder (as with so many things)
is to practice.
Does the fact that modern PCBs are soldered with that lead-free muck make
any difference? I suspect it'as actually harder to desolder such boards
(as the lead-free solder melts at a higher temperature than the leaded
stuff) so if you can manage those you'll have very few problems with the
PDP11 boards
However, most modern PCbs have a lot of SMD parts (surface mounted, no
wires/pins through holes in the PCB) which are rather different to work
with. You want to conentrate on through-hole parts at lest for the moment.
You want to non-destructively remove this component and you've already
lifted a track.
Don't tell me that you've never lifted a track. If you do I will have to
conclude that you've never worked on a PCB :-)
-tony
8 May
8 May
9:47 a.m.
Tony Duell [ard at p850ug1.demon.co.uk] wrote:
Don't tell me that you've never lifted a
track. If you do I will have
to conclude that you've never worked on a PCB :-)
I've lifted my fair share of tracks (possibly more, just natural greed I
guess).
Once or twice I've had to put down wire to make up for my clumsiness,
although
mostly I've lifted tracks on scrap that I don't care about (I just
wanted whatever
component it might have been).
Antonio
arcarlini at iee.org
9:57 a.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of arcarlini at iee.org
Sent: 08 May 2011 10:48
To: 'General Discussion: On-Topic and Off-Topic Posts'
Subject: RE: Desoldering a chopper transistor
Tony Duell [ard at p850ug1.demon.co.uk] wrote:
guess).
Don't tell me that you've never lifted a
track. If you do I will have
to conclude that you've never worked on a PCB :-)
I've lifted my fair share of tracks (possibly more, just natural greed I
Once or twice I've had to put down wire to make up for my clumsiness,
although mostly I've lifted tracks on scrap that I don't care about (I
just
wanted
whatever component it might have been).
Antonio
arcarlini at iee.org
And just for the record, I have not actually lifted a track. The track
damage is strange and I am not entirely convinced it was me because it is a
little distance from the pin, perhaps 5mm away and it is a break in the
track. It looks like I could have let the iron slip across it, but I don't
recall that happening, and the break seems too wide for the size of bit I
was using. Is it possible there might have been a latent track defect that
the heat from the iron revealed?
Regards
Rob
4:37 p.m.
On 8 May 2011 at 10:57, Rob Jarratt wrote:
And just for the record, I have not actually lifted a
track. The track
damage is strange and I am not entirely convinced it was me because it
is a little distance from the pin, perhaps 5mm away and it is a break
in the track. It looks like I could have let the iron slip across it,
but I don't recall that happening, and the break seems too wide for
the size of bit I was using. Is it possible there might have been a
latent track defect that the heat from the iron revealed?
Take a close look at the gap. It's not unusual to see board
revisions done this way--just a bit of tape on the master negatives
to do a cut in a trace. If the edges of the break look smooth and
straight under magnification, you most likely have your answer. Do
not attempt to bridge gaps such as this!
--Chuck
6:01 p.m.
And just for the record, I have not actually lifted a
track. The track
Oh you will :-). I'll admit ot having lifted my fair share of tracks too.
And damaged the odd bit of through-plating.
damage is strange and I am not entirely convinced it
was me because it is a
little distance from the pin, perhaps 5mm away and it is a break in the
track. It looks like I could have let the iron slip across it, but I don't
You won;t normally break a track by just letting the iron rub across it.
Are you sure this track break is not deliberate? Have you checked the
components connected to each side of it and made sure they should be
connected accordign to the schematics?
-tony
7 May
7 May
10:27 p.m.
On 5/7/11 11:44 AM, "arcarlini at iee.org" <arcarlini at iee.org> wrote:
I'd be tempted to suggest that you pick up some
scrap boards from
somewhere (old TV/computer from the tip) and practise.
You want to non-destructively remove this component and you've already
lifted a track.
I'd stop now and practise on something that doesn't matter. Removing
something like
a 4 pin molex power connector from a dead (recent:-)) hard drive or
similar is
probably the sort of difficulty you want?
Antonio
arcarlini at iee.org
I'd second that.. And use a good de-soldering tool. I use a Hakko 808
desoldering gun. My hot air rework station has an option for a desoldering
attachment but the gun is serving me well. Just change the flux filter
regularly and clean it out well.
6:43 p.m.
I need to desolder a chopper transistor from a PCB in the PSU of my PDP11 so
that I can test it and if necessary replace it. The trouble is that I am not
experienced with soldering and desoldering and I am having a lot of trouble
desoldering it. I have made several attempts, damaging one of the PCB tracks
in the process (should be repairable by adding a wire). I have a cheap
Weller 40W soldering iron and I have been using some narrow tips. I have one
You should be able to do it with those tools. Personally, though, I do
prefer a temperature-controlled soldering iron. YOu can have problems
with being unable to transfer enough heat to the joint to melt the
solder, particularly if it's soldered to a ground pane or similar. I know
when I tired to used a friend's 25W cheap iron some years ago, I ended up
going home to collect my Weller TCP. I simply could not get the IC's out
with the cheap one. WIth the TCP, it took a few minutes.
of those pumps for sucking out the molten solder. I
also have 2mm solder
wick (braid?).
I seem to have removed most of the solder from two of the pins, mostly with
the pump, the solder wick just does not seem to pick up any solder not
Thats what I tend to find too. I much prefer the solder sucker (pump).
A couple of hints on using the solder sucker.
Take it apart and put a smear of vaseline on the piston washer (and on
the O-ring for the front. This will improve the suction no end.
Use a fine/new tip., it's easier to get it onto the joint
Melt a little new solder onto the joint (as if you were soldering, not
deseoldering). In other words, tin the soldering iron bit, put it on the
joint, and feed in a little more sodler. Wait a couple of seconds, then
apply the solder sucher and suck.
If the connectiuon doesn't clear the first time, it's a waste of time to
try using the sucker again. Instead, resolder the connection, then try
sucking again.
matter what I do. One of the pins, however, goes onto
a track that is more
like a large area of metal and the iron does not even seem to melt the
solder there.
In which case your soldering iron is not big enough for the job.... Seen
that too many times...
The thing I really don't understand is how you desolder more than one pin at
the same time. There is always bound to be just a little solder left holding
Actually, I have had joints come completelyt clear, but it's not common.
However, the 'whisker' of solder is not strong, and generally wobbling
the pin around with pliers or the end of a screwderiver will break the bond.
Of course if you can get 2 of the pins completely free, you cna melt the
solder on the remaining one and yank the component out while the iron is
still on that joint. Then clean out the solder later.
each pin in place no matter how much you remove with
the pump or wick. So
it seems to me that you would need to have the solder in all 3 pin holes
molten, all at the same time, to be able to lift the component.
It's even more fun when you want to remove a 40 Pin DIL pacakge :-).
More serieosuly, there are/were special soldeirng iron bits to fit the
common lead arrangements of multi-pin compoonets so you could melt the
solder on all joints simulataneously. I've never found they work that well.
-tony
4982
days inactive
4984
days old
19 comments
10 participants
participants (10)
-
arcarlini＠iee.org -
ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
dave.thearchivist＠gmail.com -
dkelvey＠hotmail.com -
geoffr＠zipcon.net -
hilpert＠cs.ubc.ca -
pete＠dunnington.plus.com -
pinball＠telus.net -
robert.jarratt＠ntlworld.com