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TM500 Latch Tab fix


NigelP
 

There have been a few threads on TM500 latch repairs. Depending on which specific problem you have, this idea might be of interest.

I needed to replace/repair the latch on a TR502. The latch was of the old-style grey plastic one-part jobbie and the external part had sheared off leaving the tab with a short bit of the grey plastic inside. I managed to find some other broken latch parts in my bits box, including a larger grey tab and a smaller off-white one as well as a complete grey latch.

I discovered, as some of you will already be aware, that the tab is held on via two claws on the external end of the latch which is retained by a plastic insert so that the jaws can't spring out of the tab when pulling on it. It happens that this plastic insert is 3/32" diameter (or about 2.4mm). The insert is hidden underneath the tab, so usually invisible.... you may need to look very carefully. If you carefully centre-punch or centrally dent the insert you can carefully drill it out, preferably with incremental drill sizes, until you "almost" reach the top side of the tab. With care you can successfully remove what is left of the insert. The remains of the latch can be dudiciously removed via the side-slots in the tab.

You'll be left with a 3/32" diameter hole which extends through the end of the latch. Now, once you've swapped the "new" and old bits around you're left with the job or replacing the insert; if you don't use an insert the tab will simply pull off again next time round (as I discovered). So, what to use? Initially I tried a very short self-tap screw; this worked but didn't look very nice even though it was on the underside of the tab. I thought of a M2.5 machine screw, which would have been a better choice but decided to investigate the sourcing of 3/32" plastic rod, only to find that unless you were a very keen modeller you would be buying 5' of plastic rod in order to only use only a few millimetres of it!

Suddenly one of those light-bulb moments happened...... in the UK (and I suppose the USA and elsewhere) you can buy Johnsons Baby Cotton Buds, and guess what.... they are made using a white plastic rod of exactly 3/32" diameter! I had initially thought they might have been some compressed paper product, but no, it's plastic.

My wife now has one less in her pot and I just cut off one end and then with a scalpel cut myself a 1/8"/3.5mm length and inserted it into the hole in the tab and latch with a pair of long-nose pliers, and hey presto it works. It's not grey but hey, who uses their TM500s upside down to see????

If you are a perfectionist (and what Tek geek isn't??) then you can carefully shave it back flush with the under-side of the tab with the scalpel.


Ed (SCSKITS)
 

Nigel:

Great way to recover those seemingly one piece latches.
I find that many of the plug ins for the scope frame had that style of latch. I have not seen too many on TM500 plug ins.
I remember on some later (or maybe earlier) plug ins, the pull tab was a separate piece held on with a metal pin.

ed