Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old August 22nd 18, 12:46 AM posted to sci.electronics.repair
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Default Removing Large Electrolytics

I have just spent about 40m trying to unsolder an electro on the board of
the Tek 466 I'm currently working on. It showed a ESR of 45 ohms so I
needed to hook it out of circuit just to be doubly sure it was really
that bad.
The electros in question are all fairly large ones in the (linear) PSU
section. For some reason they've not used separate boards for the various
sub-circuits, so the PSU is just one area of a v.large board which also
has components for all sorts of other functions. Anyway, The cap in
question has 5 connections to the board: 3 equi-spaced ground tabs around
the outside that come straight from the case of the cap and the 2 + and -
wires close to the centre. Given 5 in total through-hole connections,
it's proving very difficult to remove the cap using suction pump and
solder braid cos I cannot wiggle it at all. The best solution IMO would
be to heat all 5 tabs at the same time whilst pulling the cap's case from
the other side until it breaks free. Is there any tool that enables you
to do this? I fear the amount of ****ing around I'm having to do
otherwise will lead to delamination of the PCB traces and an ugly mess.
I cannot even slip a junior hacksaw blade between the bottom of the cap
and the PCB and cut it free cos it's obscured by other components.



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Old August 22nd 18, 01:18 AM posted to sci.electronics.repair
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Default Removing Large Electrolytics

Some people use a butane torch to heat the solder joints gently while pulling on the component. Practice this technique before you do it on something you want to save. I have done this for DIP ICs.

Since you are pretty sure it is bad, I would clip the leads, destroying the can beforehand if necessary.

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Old August 22nd 18, 01:55 AM posted to sci.electronics.repair
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On Wednesday, 22 August 2018 01:18:33 UTC+1, wrote:

Some people use a butane torch to heat the solder joints gently while pulling on the component. Practice this technique before you do it on something you want to save. I have done this for DIP ICs.

Since you are pretty sure it is bad, I would clip the leads, destroying the can beforehand if necessary.


A torch is a recipe for a badly burnt board. I've always been able to move a multi-legged component at least a tiny amount while melting one or more legs, and rock it back & forth, letting the board cool well if paper. The pcb is slightly flexible after all. Paper boards are weak, vulnerable to heat & the copper comes unglued when hot.

Maybe you could cut the 3 outer tabs off flush.


NT
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Old August 22nd 18, 02:28 AM posted to sci.electronics.repair
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On 08/21/2018 07:46 PM, Cursitor Doom wrote:
I have just spent about 40m trying to unsolder an electro on the board of
the Tek 466 I'm currently working on. It showed a ESR of 45 ohms so I
needed to hook it out of circuit just to be doubly sure it was really
that bad.
The electros in question are all fairly large ones in the (linear) PSU
section. For some reason they've not used separate boards for the various
sub-circuits, so the PSU is just one area of a v.large board which also
has components for all sorts of other functions. Anyway, The cap in
question has 5 connections to the board: 3 equi-spaced ground tabs around
the outside that come straight from the case of the cap and the 2 + and -
wires close to the centre. Given 5 in total through-hole connections,
it's proving very difficult to remove the cap using suction pump and
solder braid cos I cannot wiggle it at all. The best solution IMO would
be to heat all 5 tabs at the same time whilst pulling the cap's case from
the other side until it breaks free. Is there any tool that enables you
to do this? I fear the amount of ****ing around I'm having to do
otherwise will lead to delamination of the PCB traces and an ugly mess.
I cannot even slip a junior hacksaw blade between the bottom of the cap
and the PCB and cut it free cos it's obscured by other components.




+1 for can-opening it to save wear and tear on the board. If you
measure 45 ohms ESR in-circuit, it won't be better by itself.

Cheers

Phil Hobbs
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Old August 22nd 18, 03:53 AM posted to sci.electronics.repair
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Default Removing Large Electrolytics

On Tuesday, August 21, 2018 at 6:46:24 PM UTC-5, Cursitor Doom wrote:
I have just spent about 40m trying to unsolder an electro on the board of
the Tek 466 I'm currently working on. It showed a ESR of 45 ohms so I
needed to hook it out of circuit just to be doubly sure it was really
that bad.
The electros in question are all fairly large ones in the (linear) PSU
section. For some reason they've not used separate boards for the various
sub-circuits, so the PSU is just one area of a v.large board which also
has components for all sorts of other functions. Anyway, The cap in
question has 5 connections to the board: 3 equi-spaced ground tabs around
the outside that come straight from the case of the cap and the 2 + and -
wires close to the centre. Given 5 in total through-hole connections,
it's proving very difficult to remove the cap using suction pump and
solder braid cos I cannot wiggle it at all. The best solution IMO would
be to heat all 5 tabs at the same time whilst pulling the cap's case from
the other side until it breaks free. Is there any tool that enables you
to do this? I fear the amount of ****ing around I'm having to do
otherwise will lead to delamination of the PCB traces and an ugly mess.
I cannot even slip a junior hacksaw blade between the bottom of the cap
and the PCB and cut it free cos it's obscured by other components.



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Depending on what else is nearby, a heat gun can be effective.



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Old August 22nd 18, 05:54 AM posted to sci.electronics.repair
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Default Removing Large Electrolytics


I use a Metcal which is a 40 Watt iron very well controlled but when removing caps from computer motherboards where there are no thermal reliefs to the ground plane, NO soldering iron can unsolder it alone. The pin can't conduct the heat fast enough. I also have a cheap Chinese hot air tool. Set the temp on the air tool slightly below the melt temp so it won't 'blow' any SMD parts (none on the 466) off the board. This becomes a 2 handed operation.. While heating with the Metcal, I 'auxiliary' heat the board with the hot air tool for about 20 seconds. This WILL get hot enough to use your Edsyn Soldapullt to clear the hole and not lift any pads or damage the board.

Cutting up the cap and then removing the separate pins is OK IF you can destroy it without damaging the board. I've had excellent results with the aux heating technique which is faster than dismembering the part.

Torches are WAY too brutal especially in a Tek.


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Old August 22nd 18, 11:12 AM posted to sci.electronics.repair
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On Tue, 21 Aug 2018 21:28:10 -0400, Phil Hobbs wrote:

+1 for can-opening it to save wear and tear on the board. If you
measure 45 ohms ESR in-circuit, it won't be better by itself.


Well, it's hardly surprising for an electro of this age. Clearly the
original component from a scope with a s/n indicating it was manufactured
44 years ago! What was more surprising was that only 2 out of 6 electros
in the PSU section showed abnormal readings (the remaining faulty one has
gone leaky).




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Old August 22nd 18, 12:03 PM posted to sci.electronics.repair
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On Wednesday, 22 August 2018 11:12:10 UTC+1, Cursitor Doom wrote:
On Tue, 21 Aug 2018 21:28:10 -0400, Phil Hobbs wrote:

+1 for can-opening it to save wear and tear on the board. If you
measure 45 ohms ESR in-circuit, it won't be better by itself.


Well, it's hardly surprising for an electro of this age. Clearly the
original component from a scope with a s/n indicating it was manufactured
44 years ago! What was more surprising was that only 2 out of 6 electros
in the PSU section showed abnormal readings (the remaining faulty one has
gone leaky).


Sounds about par for the course. Go back further to paper caps and it'd be a surprise to find any still working properly. And yes, micamold were paper caps.


NT
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Old August 22nd 18, 02:29 PM posted to sci.electronics.repair
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On Tuesday, August 21, 2018 at 9:28:19 PM UTC-4, Phil Hobbs wrote:
On 08/21/2018 07:46 PM, Cursitor Doom wrote:
I have just spent about 40m trying to unsolder an electro on the board of
the Tek 466 I'm currently working on. It showed a ESR of 45 ohms so I
needed to hook it out of circuit just to be doubly sure it was really
that bad.
The electros in question are all fairly large ones in the (linear) PSU
section. For some reason they've not used separate boards for the various
sub-circuits, so the PSU is just one area of a v.large board which also
has components for all sorts of other functions. Anyway, The cap in
question has 5 connections to the board: 3 equi-spaced ground tabs around
the outside that come straight from the case of the cap and the 2 + and -
wires close to the centre. Given 5 in total through-hole connections,
it's proving very difficult to remove the cap using suction pump and
solder braid cos I cannot wiggle it at all. The best solution IMO would
be to heat all 5 tabs at the same time whilst pulling the cap's case from
the other side until it breaks free. Is there any tool that enables you
to do this? I fear the amount of ****ing around I'm having to do
otherwise will lead to delamination of the PCB traces and an ugly mess.
I cannot even slip a junior hacksaw blade between the bottom of the cap
and the PCB and cut it free cos it's obscured by other components.




+1 for can-opening it to save wear and tear on the board. If you
measure 45 ohms ESR in-circuit, it won't be better by itself.

Cheers

Phil Hobbs


Right I'd hack up the component and pull pin by pin.
I do use a hot air rework station on some rotary switches...
it's faster than all that hacking.

George H.
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Old August 22nd 18, 04:03 PM posted to sci.electronics.repair
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On Tue, 21 Aug 2018 21:54:12 -0700, stratus46 wrote:

I use a Metcal which is a 40 Watt iron very well controlled but when
removing caps from computer motherboards where there are no thermal
reliefs to the ground plane, NO soldering iron can unsolder it alone.


You're not kidding. My largest iron is 40W/80W switchable. 40W won't
touch it and I'm not risking 80W! The biggest problem seems to be the cap
case - a long 1" dia aluminium tube with 3 tags at the bottom going
straight to PCB grounds. It's acting like a very effective heat sink.
Going to have to trash the caps from above.





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