Identifying shorts in CRT socket spark gaps and repairing them

[Wiebe Cazemier]

Hi,

I've been having troubles with an Eizo T766 19" CRT; the blue and red gun
occasionally turn fully on, most notably when tapping the neck board, with
visible verticle retrace for that color. At first I thought I narrowed the
problem down as being inside the CRT, because I desoldered the offending guns'
pins from the neck board, and the problem remained. However, it has come to my
attention that the problem could also very well be in the CRT socket, the
spark gaps to be precise. The "Notes on the Troubleshooting and Repair of
Television Sets" article on www.repairfaq.org says this about it:

Except for the high voltage to other places, the short may actually be

located in the CRT *socket* or even on the CRT neck board, probably in the
spark gap(s) for the problem pins. Remove the socket and test between the
suspect pins on the CRT itself. If the CRT itself is fine, the spark gaps
should be inspected and cleaned/repaired and/or components replaced.

I don't know a lot about CRT's, and their sockets, so I've got a question. What
are the spark gaps? Are those the holes next to the pin connectors? The socket
for my tube is shown in [1]. And how do I repair them (if they are what I
think they are, they are difficult to reach).

The short does not measure with the continuity tester on my DMM, and not even
with the 200 MOhm resistance tester (neither with the socket connected to the
CRT, or hanging loose, so it's difficult to test if the socket is actually the
cause. But if it were, would I measure a short between the pin connector and
ground?

[1] http://www.halfgaar.net/posts/2008-05/eizo-crt-socket

 

[Jim Yanik]

Hi,

I've been having troubles with an Eizo T766 19" CRT; the blue and red
gun occasionally turn fully on, most notably when tapping the neck
board, with visible verticle retrace for that color. At first I
thought I narrowed the problem down as being inside the CRT, because I
desoldered the offending guns' pins from the neck board, and the
problem remained. However, it has come to my attention that the
problem could also very well be in the CRT socket, the spark gaps to
be precise. The "Notes on the Troubleshooting and Repair of Television
Sets" article on www.repairfaq.org says this about it:

Except for the high voltage to other places, the short may actually
be

located in the CRT *socket* or even on the CRT neck board, probably in
the spark gap(s) for the problem pins. Remove the socket and test
between the suspect pins on the CRT itself. If the CRT itself is fine,
the spark gaps should be inspected and cleaned/repaired and/or
components replaced.

I don't know a lot about CRT's, and their sockets, so I've got a
question. What are the spark gaps? Are those the holes next to the pin
connectors? The socket for my tube is shown in [1]. And how do I
repair them (if they are what I think they are, they are difficult to
reach).

The short does not measure with the continuity tester on my DMM, and
not even with the 200 MOhm resistance tester (neither with the socket
connected to the CRT, or hanging loose, so it's difficult to test if
the socket is actually the cause. But if it were, would I measure a
short between the pin connector and ground?

[1] http://www.halfgaar.net/posts/2008-05/eizo-crt-socket

I believe the spark gaps look like disc capacitors with a slit in the
top edge.
I had a TV with bad solder joints on the CRT socket PCB,caused similar
problems.

the CRT socket could be loose for some pins.(the individual pin sockets
being spread open too much,not gripping the CRT pin tightly)

 

[bz]

Hi,

I've been having troubles with an Eizo T766 19" CRT; the blue and red
gun occasionally turn fully on, most notably when tapping the neck
board, with visible verticle retrace for that color. At first I thought
I narrowed the problem down as being inside the CRT, because I
desoldered the offending guns' pins from the neck board, and the problem
remained. However, it has come to my attention that the problem could
also very well be in the CRT socket, the spark gaps to be precise. The
"Notes on the Troubleshooting and Repair of Television Sets" article on
www.repairfaq.org says this about it:

Except for the high voltage to other places, the short may actually be

located in the CRT *socket* or even on the CRT neck board, probably in
the spark gap(s) for the problem pins. Remove the socket and test
between the suspect pins on the CRT itself. If the CRT itself is fine,
the spark gaps should be inspected and cleaned/repaired and/or
components replaced.

I don't know a lot about CRT's, and their sockets, so I've got a
question. What are the spark gaps? Are those the holes next to the pin
connectors? The socket for my tube is shown in [1]. And how do I repair
them (if they are what I think they are, they are difficult to reach).

Need to see the OTHER side of the board. Those sparkgaps I am familiar with
look like a small ceramic disk capacitor with a slit cut into the edge
perpendicular to the disk.

They might be INSIDE the body of the socket (white plastic thing on the
board you are holding).

The short does not measure with the continuity tester on my DMM, and not
even with the 200 MOhm resistance tester (neither with the socket
connected to the CRT, or hanging loose, so it's difficult to test if the
socket is actually the cause. But if it were, would I measure a short
between the pin connector and ground?

[1] http://www.halfgaar.net/posts/2008-05/eizo-crt-socket

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

 

[Wiebe Cazemier]

I believe the spark gaps look like disc capacitors with a slit in the
top edge.
I had a TV with bad solder joints on the CRT socket PCB,caused similar
problems.

the CRT socket could be loose for some pins.(the individual pin sockets
being spread open too much,not gripping the CRT pin tightly)

The article I mentioned talks of clean the spark gaps. If they are components
like you describe, how is that done? If they are components, the only ones
that could be them, is devices which look like diodes or resistors. Their
symbol is two arrows pointing towards eachother, and are connected between gun
and ground.

I had already tried running the tube with the red and blue pins of the socket
desoldered. If the spark gap is a component on the board, as opposed to
something internally in the socket (the white plastic thing in the photo),
then the problem is not the spark gap, because it wasn't connected.

 

[Wiebe Cazemier]

Need to see the OTHER side of the board. Those sparkgaps I am familiar with
look like a small ceramic disk capacitor with a slit cut into the edge
perpendicular to the disk.

They might be INSIDE the body of the socket (white plastic thing on the
board you are holding).

http://www.halfgaar.net/posts/2008-05/crt-socket-back

There are no parts except a few SMD capacitors, as far as I can see. And there
is nothing whatsoever in the white body (I desoldered it to have a look).

 

[David]

As posted, the spark gaps may be physically inside the crt
socket assembly itself. The odds of disassembly and proper
reassembly of most of these sockets is actually relatively
low. It may be done with proper tools and techniques.
What you may find is that due to arcing at the gaps or
external contaminates that the surfaces may have become
carbonized and pitted. At that point it may be best to
look for a new crt socket and just replace it.

What are the components SGH30,31,32? These are between the
cathodes and ground. These may be you spark gaps.

David

 

[Wiebe Cazemier]

As posted, the spark gaps may be physically inside the crt socket assembly
itself. The odds of disassembly and proper reassembly of most of these
sockets is actually relatively low. It may be done with proper tools and
techniques.
What you may find is that due to arcing at the gaps or external contaminates
that the surfaces may have become carbonized and pitted. At that point it
may be best to look for a new crt socket and just replace it.

This is the socket itself, the underside:

http://www.halfgaar.net/posts/2008-05/crt-socket-underside

I don't see anything that could be a spark gap. It just seems to be a piece of
plastic to connect the tube to the neck board.

A quote from David's post:

What are the components SGH30,31,32? These are between the
cathodes and ground. These may be you spark gaps.

Those are those resistor-like devices I mentioned, which' symbol is two arrows
pointing to eachother. I indeed suspected them as the spark gaps.
Unfortunately, this means that the short is really in the CRT, because the
problem persisted with the red and blue pins desoldered from the PCB. Unless
my tapping caused them to connect briefly, but I doubt that.

 

[James Sweet]

What are the components SGH30,31,32? These are between the cathodes and
ground. These may be you spark gaps.

David

They almost certainly are. I've seen the SG designation used for spark gaps
before. Some look like capacitors, some look like neon glow lamps, others
look like diodes or resistors, all function pretty much the same.

 

[Arfa Daily]

This is the socket itself, the underside:

http://www.halfgaar.net/posts/2008-05/crt-socket-underside

I don't see anything that could be a spark gap. It just seems to be a
piece of
plastic to connect the tube to the neck board.

A quote from David's post:


Those are those resistor-like devices I mentioned, which' symbol is two
arrows
pointing to eachother. I indeed suspected them as the spark gaps.
Unfortunately, this means that the short is really in the CRT, because the
problem persisted with the red and blue pins desoldered from the PCB.
Unless
my tapping caused them to connect briefly, but I doubt that.

A sharp rap or two to the neck of the CRT, using the butt end of a
screwdriver, and with the monitor / TV on its side or upside down (but NOT
on its face) can often be effective at dislodging material that has fallen
off the cathode surface into the g1-k gap. The 'resistor' looking devices
called "SG" are the spark gaps. The opposing arrows symbol is standard for
this type of device. Any slots - often with curved opposing faces - milled
in the PCB material, with copper up to the edge of the gap, are also spark
gaps. These can get dusty contamination across them. It is also not at all
uncommon to have a grounded wire ring running around the outside of all the
pins, inside the plastic base connector. However, from your description, it
certainly sounds as though the problem is internal to the CRT.

Arfa

 

[Wiebe Cazemier]

A sharp rap or two to the neck of the CRT, using the butt end of a
screwdriver, and with the monitor / TV on its side or upside down (but NOT
on its face) can often be effective at dislodging material that has fallen
off the cathode surface into the g1-k gap.

Is this also common for cathode-heater shorts? Because that is my problem.
Also, I've tried the tapping, but I don't dare tapping too hard. Your
description of "sharp rap" implies more force than I've applied thus far.

Should the rap be on the side of the tube, or on the rear side (back of the
neck board)?

I wonder how I am going to put it upside down BTW. There is nothing to support
the weight of the monitor at the back...