8-layer board, about 1050 parts - V470.jpg - V470snap.jpg
 

Chuck Harris wrote:

Robert Baer wrote:

Definitely, mechanical stress seems to enhance or aggrivate the
migration of the solder.
Monitors exhibit similar problems; one or more colors get
intermittent and / or go out.
One then must re-solder the CRT socket to the PCB.
The mechanical stress comes from the sponge in the back of the case
that presses on the metal cage around that PCB.
I have fixed dozens of monitors that way, some 2 or three times.
The one i have was bought 12-15 years ago and fixed 3 times so far.
I have called it electomigration, because of the metal flow patterns
with regard to presumed current flow in each trace.


The problem is much simpler than that. The holes in the board are
too big, and as a result, the solder is required to bridge a large
gap. Solder has next to no ability to withstand repeated flexing, so
the relatively thin solder bridge flexes and cracks.

The answer is simple all joints should be good mechanical joints. The
socket will last longer if you bend its pins outward so that they are
leaning
against the pad before you apply solder.

-Chuck
I do agree that good mechanical connections make for reliable
connections.
But.
On all of the monitors i have fixed so far, the CRT socket pins were
bent over and were touching / flat against the traces.
Furthermore, the original soldering was "blobbed" on; ie very thick
(and crappy looking).
All of that does tend to reduce and spread out the mechanical stresses.
My fixes are to remove all of the solder and replace it with a "thin"
workmanship-like hot soldering job. The fixes seem to last about as
long as the original.

8-layer board, about 1050 parts - V470.jpg - V470snap.jpg
 

Robert Baer wrote:
Chuck Harris wrote:

The answer is simple all joints should be good mechanical joints. The
socket will last longer if you bend its pins outward so that they are
leaning
against the pad before you apply solder.

-Chuck
I do agree that good mechanical connections make for reliable
connections.
But.
On all of the monitors i have fixed so far, the CRT socket pins were
bent over and were touching / flat against the traces.
Furthermore, the original soldering was "blobbed" on; ie very thick
(and crappy looking).
All of that does tend to reduce and spread out the mechanical stresses.
My fixes are to remove all of the solder and replace it with a "thin"
workmanship-like hot soldering job. The fixes seem to last about as
long as the original.

Puzzling. The current in a CRT base is insignificant... microamps on
most of the pins, and 150ma on the filament pins. I have never
had one fail, but for a case where there was 1/32 inch of solder ring
around the pin. Once I bent the pin over and resoldered, it never failed
again... In fact, I have never had one of my solder joints fail at anytime.

The reason for the big soft blobs is to limit corona on the various
CRT bits. It is done by using a good fat 60/40 solder, and a low temperature
soldering iron. 60/40 solder builds, 67/37 flows like water. 67/37 is
about half again as strong as 60/40.

-Chuck

8-layer board, about 1050 parts - V470.jpg - V470snap.jpg
 

"Chuck Harris" wrote in message
...
snip

Puzzling. The current in a CRT base is insignificant... microamps on
most of the pins, and 150ma on the filament pins. I have never
had one fail, but for a case where there was 1/32 inch of solder ring
around the pin. Once I bent the pin over and resoldered, it never failed
again... In fact, I have never had one of my solder joints fail at
anytime.

The reason for the big soft blobs is to limit corona on the various
CRT bits. It is done by using a good fat 60/40 solder, and a low
temperature
soldering iron. 60/40 solder builds, 67/37 flows like water. 67/37 is
about half again as strong as 60/40.



Chuck, did you mean "half again as strong", meaning 1.5 times as strong
or half as strong?

8-layer board, about 1050 parts - V470.jpg - V470snap.jpg
 

Lord Garth wrote:
"Chuck Harris" wrote in message
...
snip
Puzzling. The current in a CRT base is insignificant... microamps on
most of the pins, and 150ma on the filament pins. I have never
had one fail, but for a case where there was 1/32 inch of solder ring
around the pin. Once I bent the pin over and resoldered, it never failed
again... In fact, I have never had one of my solder joints fail at
anytime.
The reason for the big soft blobs is to limit corona on the various
CRT bits. It is done by using a good fat 60/40 solder, and a low
temperature
soldering iron. 60/40 solder builds, 67/37 flows like water. 67/37 is
about half again as strong as 60/40.



Chuck, did you mean "half again as strong", meaning 1.5 times as strong
or half as strong?

Yes, about 1.5 times as strong. I'm being very approximate here, as I don't
remember the exact numbers. Eutectic solder has the lowest soldering temperature,
and just about the highest strength of tin/lead alloys.

-Chuck

8-layer board, about 1050 parts - V470.jpg - V470snap.jpg
 

Chuck Harris wrote:

Yes, about 1.5 times as strong. I'm being very approximate here, as I
don't
remember the exact numbers. Eutectic solder has the lowest soldering
temperature,
and just about the highest strength of tin/lead alloys.

I found some numbers:
http://www.boulder.nist.gov/div853/l...ree/part1.html
Just past half way down, they compare various tin lead solders.

8-layer board, about 1050 parts - V470.jpg - V470snap.jpg
 

Chuck Harris wrote:

Robert Baer wrote:

Chuck Harris wrote:


The answer is simple all joints should be good mechanical joints. The
socket will last longer if you bend its pins outward so that they are
leaning
against the pad before you apply solder.

-Chuck

I do agree that good mechanical connections make for reliable
connections.
But.
On all of the monitors i have fixed so far, the CRT socket pins were
bent over and were touching / flat against the traces.
Furthermore, the original soldering was "blobbed" on; ie very thick
(and crappy looking).
All of that does tend to reduce and spread out the mechanical stresses.
My fixes are to remove all of the solder and replace it with a
"thin" workmanship-like hot soldering job. The fixes seem to last
about as long as the original.


Puzzling. The current in a CRT base is insignificant... microamps on
most of the pins, and 150ma on the filament pins. I have never
had one fail, but for a case where there was 1/32 inch of solder ring
around the pin. Once I bent the pin over and resoldered, it never failed
again... In fact, I have never had one of my solder joints fail at anytime.

The reason for the big soft blobs is to limit corona on the various
CRT bits. It is done by using a good fat 60/40 solder, and a low
temperature
soldering iron. 60/40 solder builds, 67/37 flows like water. 67/37 is
about half again as strong as 60/40.

-Chuck
TV sets seem to *never* have the problem, because they do not have
the stress from a sponge in the back, and monitors in storage also do
not have a problem until years after use.

I know the currents are small, but on monitors, it seems the cathode
connections are the first to go.