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Old 12th Jan 2021, 11:00 am   #1
Courtney Louise
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Default Broken EHT lead. What can I do to fix this?

Hi all

This is an American Motorola Black and White TV from 1973.

It’s part of a Pong video game having the tuner disconnected and the audio/video fed direct.

The LOPT has a plug attached to the end of this wire but has become dislodged.

How can I fix this as the TV model number doesn’t come up with any google results for service information etc.

Kindest

C
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Old 12th Jan 2021, 12:38 pm   #2
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Default Re: Broken EHT lead. What can I do to fix this?

Quote:
Originally Posted by Courtney Louise View Post
Hi all

This is an American Motorola Black and White TV from 1973.

It’s part of a Pong video game having the tuner disconnected and the audio/video fed direct.

The LOPT has a plug attached to the end of this wire but has become dislodged.

How can I fix this as the TV model number doesn’t come up with any google results for service information etc.

Kindest

C
How long is the cable ?
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Old 12th Jan 2021, 12:40 pm   #3
G6ONEDave
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Default Re: Broken EHT lead. What can I do to fix this?

I can think of 2 possible fixes but ideally it would be best to replace the LOPT. Also don't try any of this unless you know what you are doing, as it could cause serious problems if not done correctly.

1. Remove the metal contact from inside the cap by pulling it out through the large hole. Next thoroughly clean the rubber cap to remove all the discolouration. Take a 75mm length of wire with insulation from the centre of a suitable coax cable and thread it through the small hole in the cap and grab the end and pull it out through the large hole in the cap. You should now have a cap with wire sticking out of both holes. Solder the end of this wire to the metal contact in same place as original was. Don't produce any spikes in the solder, it needs to be domed ideally. Now pull the wire back through the small hole of the cap until you get the metal contact back in place. Try not to break the solder joint during this operation, or you will have to start over. Cut the new wire to approx. twice the length of the wire leaving the LOPT and strip back the insulation on both wires by about 5mm. Slip a section of adhesive lined heatshrink over the wire from the cap. The heatshrink wants to be about two thirds the length of the wire leaving the cap. Now lay both bare wires side by side, or if you can twist them round each other even better. Solder them together and cut a 5mm long section of insulation from the coax middle. Slice the insulation length ways and cover the solder joint with it, then slide the heatshrink over it and shrink into place.

2. Clean both the rubber cap and the thicker insulation from the LOPT to remove all the discolouration. Cut about half of the small holed sleeve away from the cap. Now cut a hole in the cap top, so that the metal contact is visible at the point where the original wire conected. Place a length of adhesive lined heatshrink over the thick insulation of the LOPT. Now bare and tin 4 or 5mm at the wire end from the LOPT. Next feed the wire into the cap via the small hole and once visible over the metal contact, solder it in place. Push the heatshrink over the small holed sleeve of the cap and shrink into position. This leaves an exposed contact ot the top of the cap. This hole needs to be filled with silicon but not bathroom type. The silicon needs to to be acetate free, otherwise the acetate given off wilst curing may well cause corrosion to the soldered joint.

Neither method is ideal but given that a replacement LOPT is probably in the unobtanium category, is a way to get the set working again. BTW the cleaning is essential as the staining may contain conductive areas, which you don't want, especially with EHT insulation! Likewise smooth joints, as spikes can emit corona, which is something else that you don't want.
Dave
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Old 13th Jan 2021, 12:59 pm   #4
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Default Re: Broken EHT lead. What can I do to fix this?

Thought of this method this morning.

3. Again clean the cap thoroughly, then stand the cap on a work bench so that the caps large hole is facing up. With a sharp knife carefully cut down the side of the large hole towards the sleeve section. Then cut along the sleeve section, once done extract the metal contact and solder it to the wire coming from the LOPT. Now fit the metal contact and wire back into the cap. The cut opening can now be resealed with a suitable adhesive to rejoin across the newly cut slit. This is probably the best method of all 3 and would be less obvious that anything has been done. Just be very careful not to injure yourself. It should also go without saying but don't try any of this repair with the set powered.
Dave
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Old 14th Jan 2021, 8:42 pm   #5
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Default Re: Broken EHT lead. What can I do to fix this?

Just to borrow the thread is the old style wire cored ignition cable suitable for replacement of the cable ? Note I don’t mean the carbon coated glass fibre. The ignition wire and high voltage neon sign wire is still easier available.
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Old 15th Jan 2021, 10:54 am   #6
G6ONEDave
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Default Re: Broken EHT lead. What can I do to fix this?

Whilst ignition and neon sign wire might be easier to obtain for some, I would not have said that they were generally easier to obtain. For me coax cable is far easier to obtain and there is plenty of scrap coax around as well. I can't vouch for neon wire as I have never used it. Re vehicle ignition wire, this is generally not as flexible as the wires used in tv/monitor EHT circuits, also ignition wire is generally quite a bit larger in outside diameter, so there would probably be difficulties in getting it to fit inside the moulded sleeving of the EHT caps. Either way you need to be mindful of the insulation voltage rating, which if lucky will be printed on the outer insulation or specified at point of purchase. I use amy general rule that wiring coming out of a LOPT needs to be able to safely carry between 2Kv upto 10Kv and wiring to a final anode could be between 8Kv upto 30Kv. The actual voltages are down to the manufacturers design and component ratings and my rule is just a general guide, not a guarantee. There will always be an exception to my rule!
Dave
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Old 16th Jan 2021, 3:14 pm   #7
Welsh Anorak
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Default Re: Broken EHT lead. What can I do to fix this?

An old colour TV LOPT is a good source of cable good to 25kV and also often can yield those handy silicone rubber 'top hats'.
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Old 16th Jan 2021, 5:04 pm   #8
Alistair D
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Default Re: Broken EHT lead. What can I do to fix this?

Dave; I have a reel of Radiospares EHT cable here. It is double sleeved and 5mm diameter. If you want a length PM me your details. FOC+postage

Al
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Old 17th Jan 2021, 4:04 pm   #9
G6ONEDave
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Default Re: Broken EHT lead. What can I do to fix this?

Thanks for the kind offer Al. I currently don't require any EHT cable, as I do also have a few ex Philips final anode leads, as well as some screened types. I was just trying to offer some helpful suggestions for those who don't have access to such cables.

I wonder if Courtney has sorted out the LOPT connector problem yet.
Dave
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Old 17th Jan 2021, 4:43 pm   #10
Alistair D
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Default Re: Broken EHT lead. What can I do to fix this?

Another goof on my part. That should have been Courtney.

Al
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Old 23rd Jan 2021, 12:44 pm   #11
Danny
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Default Re: Broken EHT lead. What can I do to fix this?

Is this on the end of the rectifier stick. If yes I would just use a piece of wire and solder it to the end the secret is no spikes or strands a nice round blob . The insides of the connector can be priced out and put the end of you wire through the hole and solder it back . If there is no metal parts near the wire and you keep it short normal wire can be used any bear joints can be covered with non corrosive silicone. I have done this many times with no problems
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