1. Home
  2. Electronics Repair
  3. Identifying shorts in CRT socket spark gaps and repairing them

Identifying shorts in CRT socket spark gaps and repairing them

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

formatting link
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]
formatting link
Reply to
Wiebe Cazemier
Loading thread data ...

Wiebe Cazemier wrote in news:7a2a3$4819d907$d4cc82be$ snipped-for-privacy@cache2.tilbu.nb.home.nl:

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)

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

Wiebe Cazemier wrote in news:7a2a3$4819d907$d4cc82be$ snipped-for-privacy@cache2.tilbu.nb.home.nl:

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).

--
bz    	73 de N5BZ k

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

bz+ser@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap
Reply to
bz

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.

Reply to
Wiebe Cazemier

formatting link

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).

Reply to
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.

Reply to
Art

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

David

Reply to
David

This is the socket itself, the underside:

formatting link

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.

Reply to
Wiebe Cazemier

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.

Reply to
James Sweet

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

Reply to
Arfa Daily

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...

Reply to
Wiebe Cazemier

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.