Telequipment mains lead replacement ideas?

[MrBungle]

I've recently got hold of a D755 which appears to be working. However the mains plug has disintegrated and is held together with tape. It needs replacing. Does anyone have any ideas on suitable methods of replacing these. I can't find a replacement connector that will fit in the hole. I did consider a captive lead but there's not much space on the rear panel to mount something securely. Only option I can see is drilling a hole to the left of the fuse holder and adding a cable gland.

Ideas welcome!

Picture attached. Connector is at the bottom.



(loose wires are because I've got the PSU board out to replace the caps)

[Pinörkel]

On my D755, the previous owner has, unfortunately, gone with the solution of drilling a hole in that spot. I have a 3D printed replacement for the TQ connector in the making using a PLA or ABS enclosure with inserted brass quick disconnect male crimp terminals. The prototypes fit quite well into the connector. However, before I can consider this to be safe, I need to measure the insulation resistance of the enclosure material. For 3D printed materials, there are usually no official electrical specification available. Alternatively I could try to insert some isolated female crimp terminals. If it works, I can make my 3D files available for free.

An alternative could be, to 3D-print a mold for insertion of a PCB with brass plates, and then injection mold rubber into it to get the final connector.

If the connector does not need to be functional and nice looking one could just take some isolated female crimp connectors of appropriate size, similar to the ones shown here and put them on the pins in the connector. However, this solution would not be secure against pulling and has no polarity protection.

[ChristianFletcher]

If your interested I made high voltage connectors using PLA for my Hipot tester they were good to over 40kv. I’m not sure if the performance would degrade with time as PLA does absorb water. You can of course print using ABS the electrical characteristics of which are well known. I have printed several connector for use on test gear and radios and they are still in regular use 5 years later. I have found the modern modified PLA to be almost as good as ABS in most applications but every manufacturer has its secret source.

I think I would be drilling a hole and fitting a cable. You could always install a female IEC connector to a short cable. I often print a cable gland that fits the shape of the old connector. My choice is normally the IEC connector route as I hate special cable or long leads trailing from equipment.

[MrBungle]

Thanks both. I want to avoid 3dp for this one as I quite frankly can’t be bothered to sit there in F360 for hours

I came up with a third option last night. If I take the old connector (both halves) and drill out the pins then use the entire assembly as merely an entry point to the scope that may work as well. I’d glue (epoxy) the whole connector assembly both plug and socket into one piece and just bring the three internal conductors for the cable into the unit and terminate inside. Thoughts?

Result will be a captive lead but no extra holes to drill and it will be right angled unlike a cable grommet.

[GrimJosef]

How much current does the D755 draw ? Would an IEC type C5/C6 combination fit - they're rated up to 2.5A ?

As far as electrical compliance of other materials goes, one of the requirements concerns their behaviour in the event of continuous local sparking. This can be a tough thing to test for with a homebrew design.

EDIT: I see there's a 1A/240V fuse specified. If that's the mains fuse then C5/C6 should be adequate. The panel plug might have to be mounted on a plate, of course.

Cheers,

GJ

[turretslug]

I'd wondered about an IEC C5/C6 option here but I'm sure I came across this situation with a TQ 'scope a decade or so ago and decided that even that was going to be nigh-impossible. There was a modern three-pins-in-line connector with mechanical polarisation that used to feature on many Dell laptop PSUs (imagine a flattened C5/C6) that would be ideal here but I've never been able to track it down as a separately available component.

It's a shame that that voltage selector occupies so much real estate- were it mine, removing it and hard-wiring for UK mains would be on my list of options, giving plenty of room for an IEC C13/C14 fitment. I dislike both captive mains leads and voltage selectors, so tend to remove/avoid them but I appreciate that not everyone thinks that way.

[G6ONEDave]

If you are concerned about insulation of a 3D printed plastic body, you could always test across the terminals with a Meggar device. This could be done with just the connector sat on the bench for testing. If it shows infinity on a 1Kv test voltage it will be OK at mains voltage. 10Megohm resistance is generally accepted as the safe minimum requirement for 240v ac mains leakage. Unless the filament plastic contains carbon or some other conductive material I would expect any leakage resistance to be very high.

Dave

[Pinörkel]

Originally Posted by G6ONEDave

If you are concerned about insulation of a 3D printed plastic body, you could always test across the terminals with a Meggar device. This could be done with just the connector sat on the bench for testing. If it shows infinity on a 1Kv test voltage it will be OK at mains voltage. 10Megohm resistance is generally accepted as the safe minimum requirement for 240v ac mains leakage. Unless the filament plastic contains carbon or some other conductive material I would expect any leakage resistance to be very high.

Dave

That is approximately, what I had in mind for testing. Unfortunately, I do not own a 5kV insulation resistance tester. The Chinese ones do not look too trustworthy and known brand ones often cost 500+ €. Too much money for what I could use such a device for.

As far as I see it, the issues with 3d printed materials are that it could absorb water and that material properties can differ significantly from raw material properties after extrusion with a 3D printer. In addition to that, PLA and ABS are very sensitive to heat. They slowly deform starting with temperatures as low as 60° C and they become liquid at ~200° C. At the moment, I can not see how temperatures like this could occur in a connector with sufficiently sized contacts and contact areas, especially with a main fuse rated this low, but better safe than sorry.

I have attached a few pictures of my current prototype. The case can be opened for cable installation via a sliding mechanism. My initial plan was, to insert copper strips with sufficient cross sections as the contacts and crimp the wires of the power cord onto them. Maybe I can directly use some existing 2.9 mm quick connect male crimp terminals for that.

[MotorBikeLes]

You are referring to the LEAD as faulty, not the scope socket? The leads have been unavailable for more than 30 years, but I have a few of the socket parts.
I have replaced quite a few of these. There used to be a TEK part that fitted perfectly, with a cable restraint, so you just fitted a new lead permanently in the scope. I may have one somewhere, and likely the part number. However, in most instances I have cut out a suitable piece of tufnol just larger than the hole, drilled fixing holes, and then a central hole to take a cable restraint. It has always worked for me.
Les.

[MrBungle]

I've managed to sort it in the end. I tried gluing the entire assembly solid with the cable installed in it but it turns out the adhesive I have (devcon 5 minute) was not good to hold it together. So I have installed a hefty cable gland next to the fuse holder. This appears to have worked.

Including pictures of refurbished power supply at the same time. The main filter capacitors had leaked badly.







All working now, surprisingly! Wonder what will snuff it next. Hopefully not the HT.

[Julesomega]

I'd certainly like a printed body to replace mine, which was inexplicably cut short (maybe the cable had been fed through the back of a shelf unit or something). This was not the only non-standard mains connector that Telequipment used - why did they have to do that?

[MotorBikeLes]

I have never seen that first one on a TQ scope. Earlier units all had an attached cable. Only later did they introduce the "flat" one. I think it was made by Bulgin, though I never saw it on anything else.
Les.

[factory]

Originally Posted by Julesomega

I'd certainly like a printed body to replace mine, which was inexplicably cut short (maybe the cable had been fed through the back of a shelf unit or something). This was not the only non-standard mains connector that Telequipment used - why did they have to do that?

That other connector is a German Wieland Electric connector, see number 25 here; https://www.plugsocketmuseum.nl/PowerCord1.html
Could it possibly be a replacement?

They seem to be used for lighting, RS have mains leads with them, not sure which socket would be suitable though.
https://uk.rs-online.com/web/p/light...ctors/1576479/

David

[dglcomp]

Just had a brainwave, what about the mains connector for a sewing machine, slimline and enough contacts for earthing if needed.

[G6Tanuki]

Those "Wieland" connectors are often used in the power-distribution strips fitted to upper-class-office/finance-house-dealer-room desks and workstations: could be worth seeing if there's a local office-refurbishment business who may have a few of them as junk.

[Pinörkel]

Here are some pictures of my probably final prototype. It consists of two 3D printed parts (tested with PLA and ABS), three blade receptacle vibration-proof crimp connectors (width: 2.8 mm, thickness: 0.8 mm, souce) and a power cable of choice. The 3D printed parts have easily removable support materials and brims, although with ABS it can be a bit tricky to make it stuck on the build platform. As can be seen in the second image, the crimp connectors need some post processing with a pair of pliers (left two connectors are modified). The front two thirds of the insert have to be straightened. As a first step, a three stranded power cable has to be fed through the upper part of the connector. It is designed to be a very tight fit, so cable with matching thickness has to be selected. Then the connectors can be crimped to the cable strands. It is important to let all three strands have different length to fit into the rectangular holes in the lower part of the connector, as can be seen in picture four. The yellow/green protective earth wire has to be the longest one. The rectangular holes in the lower part have an end stop for each strand to match the connector rods of the scope connector in a way so that the protective earth connector connects first and disconnects last. In this position there is an indentation in the geometry into which the hook of the crimp connector engages. So, once it is in, it will not come out again. After inserting the cable like shown in picture four, the upper part of the connector can be slid over the lower part and the connector is complete.

The plug is quite robust and has no parts that can break easily. Even when the top is not closed, it is impossible to accidentally touch the conductors with your hand. I added some riffles like on the original for better grip. The prototype connector makes a firm and very high quality connection. The resistance between the mains plug and the solder points inside the scope is smaller than 0.1 Ohms, which is way smaller than the resistances of the crappy cable through a drilled hole in the back panel of my D755 installed by the previous owners. Unfortunately, I have not yet had the opportunity to test the insulation resistance of the connector with a certified high voltage tester. The material should only be an issue, if heated above 60° and put under mechanical stress simultaneously. At least in my use case, the probability for this to occur should be way lower than anything else in the scope blowing up.

[Pinörkel]

A picture of the whole cable and a silly little animation of the connector components. I can make the 3D-files for the connector available upon individual request via PM, but only under the condition that they may only be used on the users own responsibility. I do not guarantee this to be safe in any way and deny any responsibility or liability for potential safety risks of the connector.