Broken Space Invaders switch?

pgru

07 Apr 2021, 21:16

Hi, don't known if it is a good place to post, but thanks in advance for reading and reply.
I have an Amiga 2000 keyboard that I think is the "space invaders/bear version" (according to sticker on front, no sticker on back, and Caps Lock, plus color of Amiga keys).

The main problem is as far as I remember with 'A' key - If pressed it prints on screen like asdsdffdfdf -similar for example, in fact it turn on Caps Lock and gives some letters, that are in line with other keys according to Amiga hardware manuals for programmers, not sure but it may be called ghosting or something like this.

First I was thinking that just a line on PCB is broken - but in that case shouldn't I just get nothing on screen?

Now I am thinking that just "space invaders/bear" keyswitch is broken causing "short circuit"(?) - according to what I found on the Internet(and thank You all for sharing Your knowledge) the golden plates(?) under the keycap are easy to broke(maybe even during not so usual usage, keyboard was used on knees, at these times I didn't had enough money for good computer desk), or maybe just some pins are not soldered correctly?

What do You think? Is the keyswitch repairable(how?) or I should find the replacement(where and how much?) and solder it?

User avatar
Muirium
µ

07 Apr 2021, 22:00

Pics would be good. Have you taken the cap off? They can be extra fiddly on space invader switches.

wiki/Hi-Tek_Series_725

How to take the caps off safely without springs flying everywhere:

viewtopic.php?f=2&t=19983

Rayndalf

07 Apr 2021, 23:23

The switch could be chattering, but it sounds a bit more complicated. If they are white linear space invaders I could send you one, but you could test by swapping the suspect switch with a lesser used key you know is good. If the problem continues then it might be a problem with the PCB.

I also have a Commodore PC-10(?) keyboard that uses the same switches, so I think Commodore was partnered with NMB/ HiTek for a while.

pgru

11 Apr 2021, 17:55

Thanks for fast reply
I have read, watch and finally used tool on letter A of my A2000 keyboard.
However - I removed the keycap with slider inside(so didn't watch in full legendary space invaders face :-( ), good that at least the spring don't "go into space", and remained on position. There was a lot of dust there - removed them with finger, and small wooden stick (just the same You use in kitchen...). Sadly I don't lubricated that - don't have krytox. Is the Vaseline(from pharmacy) good enough for this slider type? Should I use some grease/WD40 on spring? I found that also isopropyl alco. may help, but the same source says that it can damage plastic?

Sadly I didn't checked if it is working correctly after removing dust, have some problems with Amiga, and it would take some time to install drivers and use Catweasel (which have the ability of handling Amiga keyboards) on other computer.
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Rayndalf

12 Apr 2021, 00:50

Looks like the stem came off with the keycap. It'll be easier to reassemble if you remove the slider/stem from under the keycap and put that back on first, then reattach the keycap after.

Pretty sure those are linears though.

pgru

12 Apr 2021, 09:17

Thanks for reply, however I inserted the keycap with slider/stem in, and it looks like it working? Need to check it with Amiga or Catweasel...

User avatar
hellothere

Yesterday, 00:29

pgru wrote:
11 Apr 2021, 17:55
Is the Vaseline(from pharmacy) good enough for this slider type? Should I use some grease/WD40 on spring? I found that also isopropyl alco. may help, but the same source says that it can damage plastic?
No to all of this. Seriously. You can badly damage your keyboard using any of that. If you want a cheap lube, use this. You also need very, very, very little lube per switch. Make sure the switch is clean before lubing.

Dust can be removed with compressed air or a fine brush and a vacuum cleaner.

It is extremely easy to destroy the contacts on Hi-Tek 725 switches. It's a little unfortunate that you're using this as your first keyboard to try to lube. However, there are some really good videos on YouTube.

===========

> PCB is broken - but in that case shouldn't I just get nothing on screen?
Not necessarily. I've got a keyboard with a "broken" PCB where half the keyboard works fine. In my case, I just need to replace a diode.

> with 'A' key - If pressed it prints on screen like asdsdffdfdf -similar for example
Desoldering the 'A' key and soldering in a known-good switch is probably the easiest first step. If problems persist, you might have to get a multimeter to make sure there isn't a trace that's bad on the PCB (i.e. continuity check) -- or just unscrew the case and see if you have globs of rust all over the place.

Rayndalf

Yesterday, 01:14

I mean I've sprayed the silicone based version of WD40 directly into switches without any ill effects, but I knew I was living dangerously.
Isopropyl alcohol would work as a decent contact cleaner, but you might want to lubricate after you use it.

But this is coming from someone that cleans cases and keycaps with brasso and washes flux off of PCBs in a sink with a toothbrush.

4_404

Yesterday, 01:38

hellothere wrote:
Yesterday, 00:29
pgru wrote:
11 Apr 2021, 17:55
Is the Vaseline(from pharmacy) good enough for this slider type? Should I use some grease/WD40 on spring? I found that also isopropyl alco. may help, but the same source says that it can damage plastic?
No to all of this. Seriously. You can badly damage your keyboard using any of that. If you want a cheap lube, use this. You also need very, very, very little lube per switch. Make sure the switch is clean before lubing.

Dust can be removed with compressed air or a fine brush and a vacuum cleaner.

It is extremely easy to destroy the contacts on Hi-Tek 725 switches. It's a little unfortunate that you're using this as your first keyboard to try to lube. However, there are some really good videos on YouTube.
Lube is highly unlikely to fix a faulty switch, especially for the behavior described here. As such, I wouldn't bother with lube until you get the keyboard working. Also, there's little point in lubing a single switch - if you're going to lube a keyboard, you really need to do the whole board. That takes time, and if you're going to that sort of effort, it's not worth cheaping out, and you should get the right stuff - Tribosys, Krytox, superlube, or another well established keyboard lubricant. As above, certainly don't use vaseline/WD40. Lubing switches, especially space invaders, is a fair bit of work, so I would recommend doing it properly, or saving yourself the time.

Isopropyl alcohol should not harm most plastics, and I can confirm it's fine on these switches, but it's also not a lubricant - it's really just for cleaning oily/sticky/greasy substances like lubricant and for when you want to wash something but avoid the side effects (hard to dry, rusting, minerals/contaminants) of water.

These switches can be a bit fiddly to work on, but they're really not as bad as everyone says, as long as you are careful and don't just force them together. I wouldn't go opening them all up for no reason, but if you should not be discouraged if you want to improve/repair them. Just make sure that the two contact arms are pushed outwards/apart by the wedge on the slider, rather than crushing them downwards. If you do damage or bend the contact arms, it is usually possible to repair them - I find putting the top slider on, pushing it down all the way, then getting a small tool (e.g. small pliers or a toothpick) to bend the top of the damaged contacts back so that they touch when the switch is pushed down. I've pulled apart 3 or 4 boards worth of these switches and damaged a couple on my first time, but was able to repair them all using this method.

User avatar
hellothere

Yesterday, 17:15

4_404 wrote:
Yesterday, 01:38
Isopropyl alcohol should not harm most plastics
Depends greatly on the percentage. I've got some 99% over here. I haven't directly tried it on key switch parts, but it definitely discolors other plastics ... and skin.

4_404

Today, 02:04

hellothere wrote:
Yesterday, 17:15
4_404 wrote:
Yesterday, 01:38
Isopropyl alcohol should not harm most plastics
Depends greatly on the percentage. I've got some 99% over here. I haven't directly tried it on key switch parts, but it definitely discolors other plastics ... and skin.
Strange, I used to rinse all my Alps and space invaders (and heaps of other old computer parts) in 99% IPA by hand and never noticed any discolouration to parts (or hands). Maybe it wasn't really 99%...

Rayndalf

Today, 02:29

4_404 wrote:
Today, 02:04
Strange, I used to rinse all my Alps and space invaders (and heaps of other old computer parts) in 99% IPA by hand and never noticed any discolouration to parts (or hands). Maybe it wasn't really 99%...
If it's anything like hydrogen peroxide then it breaks down and loses potency after some time.
I haven't experienced any discoloration myself (but I haven't used 99% as far as I know).

pgru

Today, 13:06

I want to say BIG Thank You for all replies and sharing knowledge on Internet(films helped also a lot). I checked the keyboard on computer with Catweasel controller and "A" is working correctly, like most of the keyboard. Maybe just carefully cleaning from dust helped a lot.

Sadly some other keys are not working(no reaction) - about 5 as I remember, with some being letter, and digits not only from numeric.
I will try to also carefully clean them from dust. Just in case I remove keycap correctly - is removing a slider with other side of tool that I use(shown on photos) a good idea? As I watched videos there are just pliers, not the mechanical keyboard tool that I have?

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