Note: This is a post I made at stargazerslounge.com in 2012, pasted here for my own blog.
Finally, I think I’ve cracked it. I’d always had some dicky power connection problems with my 8SE mount, and even after replacing the plug on the end of my SkyTron power cable with one that I believed was a better fit, it still showed problems. I ordered matching plug and socket from Maplins, but even then it was all too easy to lose power from just the slightest tug on the cable.
While I had the mount apart (the power socket and switch are on a convenient panel which unscrews – it is not necessary to dismantle the whole mount to remove this panel, it is just a couple of screws) I had a closer look at the socket.. no wonder it is so easily disrupted, the main center pin is fine, it’s the pathetic small outer contact that is the problem; it doesn’t connect to the main metal part of the socket chassis as I expected, but is a small contact right at the bottom of the socket, meaning that the slightest movement could break the contact. This may be fine for most applications of this socket type but where there is a chance that the cable may be snagged it is a terrible choice in my opinion.
I had read somewhere about replacing it with a BNC connection, or saw another scope that used one, something like that, so that is exactly what I have done.
One order of matching BNC socket and plug from Maplin’s later…
(despite the picture on the Maplin website, it is silver in colour and not gold)
I needed to make my own hole in the plastic panel but this was easy enough to do with a small drill bit and some needle files to finish it off; I was careful to trim the hole so that it has a flat edge for the BNC socket, otherwise it would be possible to rotate the BNC socket which would make using it more difficult.
One trick I missed but got lucky with was marking which wire goes to the center pin (positive), I had to take a guess at their relative positions as I had removed the old socket. If I were to do it again, I would mark the wire with a red marker pen or such as they are fairly nondescript grey ribbon cable wires that disappear into the mechanism.
I made sure that I applied heat shrink to all of the connections to prevent any dew droplets from causing a short.
A quick test and it all works, the connection is rock solid and I believe should never break under normal conditions. The wire would probably get pulled out of the BNC plug before it broke due to the BNC losing connection! Perhaps that is a slight loss of a ‘safety feature’, but in my experience if the cable is wrapped around it will be pulling sideways and would not pull the plug out of the socket, if I snag my foot on the cable, well that would be my hard cheese.
It should be noted that I am fairly competent with a soldering iron, but if you can solder small wires together neatly then that should be all the skills required.
I’ll probably plug the hole with something. I’m optimistic that this should be the end of the power problem, only time will tell, the real test will be at 12am on a cold January morning.
And further posts that I made on the thread…
It should be noted that after some experimentation it turns out that the BNC plug from Maplin is not as good as it could be… I originally tested the BNC socket using a different BNC plug, but the one from Maplin is a slightly different design (not as good, in my opinion). The metal flanges that surround the center pin need to be pushed outwards slightly, as it is these that contact the outer metal of the socket chassis (on the inside of the shaft). Difficult to explain if you don’t have a BNC socket handy for reference. The one I tested with had a white plastic collar inside that kept these flanges out – see pic below:
Whereas the BNC plug from Maplin was like this:
For the sake of a fraction of a penny’s worth of white nylon it is suddenly not as good. Those metal flanges need to be kept pushed slightly outwards to make good contact, otherwise when the plug or cable are moved or pulled it can break the contact and result in the mount / handset resetting. I verified this by trying it with the flanges pushed in and then pushed out, out being very solid. Not sure how long it will keep functioning well, but I should at least know what the problem likely is if it shows any signs of intermittent power.
I’m not sure where one buys BNC plugs with the white collar, this one came from an existing cable that I picked up from a car boot sale (sealed unit, I won’t be taking it apart).
A further update regarding the BNC plug…
I picked up a couple of right-angle BNC plugs from an electronics shop in town, they have the white collar (I asked about the collar, the guy said he’d never heard of a BNC plug without one and gave me a bit of a quizzical look). Here it is on the end of a Skytron cable:
Fits well, works like a charm, and as a bonus doesn’t stick out as much so shouldn’t snag. Requires no soldering too which is handy.
And then finally an idea for a safety release cable:
I realise there is another trick here to help with the snagging cable potential problem. The BNC connection is fine, but an added safety feature could be an in-line plug and socket that will pull apart should the cable be snagged suddenly. I have already used such a pairing in a custom power lead configuration for my CG-4 dual axis set up (I wired up a regular 4xAA battery pack instead of the bulky 4xD cell battery pack). If this was installed a foot along the cable from the BNC socket it would be easy to reach and find, I don’t foresee any intermittent contact problems with this method because the plug and socket pair I purchased are rock solid and fit tightly together, in fact the original SkyTron cable would probably fit this socket.
Here’s a photo showing the 4 x AA battery pack with short fly lead to a connector, and the two connector types, which I use to drive my CG-4 mount. Also the BNC right-angle connector just because it was to hand (used with the 8SE, not CG-4). These two connectors are a very firm fit, think I bought them from eBay – bought about ten of each (male and female) in case I wanted some for future projects, they were so cheap it only came to a few quid.
I have since sold my 8SE Goto mount as I was no longer using it for anything and needed the space.