Goldstar MSX keyboard issue

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By MichelM

Expert (80)

MichelM's picture

27-05-2016, 18:06

My Goldstar FC 200 has one single key that isn't working (the "L" key). All other keys work just fine.
I opened it up, to see if it might be dirty or corroded, but it looks good to me (but I don't have very much electro technical skills).

Besides cleaning it, or blowing air through it, which didn't resolve the issue, I don't know how to proceed. I might try out some contact spray.

What else can I do to make this key work again?

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By Lord_Zett

Paladin (807)

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27-05-2016, 18:32

soldeer

By MichelM

Expert (80)

MichelM's picture

27-05-2016, 18:45

Hmmm. Yes. I was afraid of that. No soldering experience here, so definitely not something I want to perform myself.

By Wild_Penguin

Hero (638)

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27-05-2016, 21:15

I find it a bit weird that people just tell to solder... if the soldering has come undone, it should be easy to spot (sometimes with the help of a magnifying glass) - look for a crack around the pin(s), or solderings with obviously too litlle solder (or cold solderings etc, which might have worked until now, but start giving symptoms only when the device is old). In my experience, the issue can be at least as likely in the mechanism iself as in the solder. For example, on my HX-10 there were around 9 keys that didn't work, and none of them had a bad soldering. That being said, the soldering can come undone over time, since in some keyboard models the repeated pressurre of pressing the keys will put some, or all of the mechanical pressure, on the sodlering joint itself. This is more likely especially if some of them have been badly soldered at the factory.

But the bottom line is: bad solderings can be seen (or alternatively, measured with a multimeter). There is no reason to solder them blindly.

Also, I haven't dismantled a FC-200 keyboard, but have you opened the mechanisms of individual keys itself? I.e., seen the contact points (that will short when a key is pressed)? Without that, you can not clean them properly.

By MichelM

Expert (80)

MichelM's picture

27-05-2016, 21:32

So, just out of curiosity, what was the issue with those 9 keys on your HX-10? How did you end up making them work again?

By Wild_Penguin

Hero (638)

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27-05-2016, 21:44

Probably some oxidization on the contact points. I opened up the affected keys, and cleaned the contact points with 96% ethanol and cotton swabs (contact spray would have probably worked, too, but I had some alcohol handy and I was sure it will not leave any residue). I have actually documented this quite well, see this thread and some pictures! :)

FWIW, I also checked the solderings but didn't touch them (save for one key to learn to open the mechanism). Bad /undone soldering is certainly a possibility, but not the only possibility...

By tvalenca

Paladin (747)

tvalenca's picture

27-05-2016, 22:14

Most MSX keyboards don't use individual switches, so one can not just tell that when a key don't work you have a bad solder joint. My HX-22 has indeed individual switches (opened it yesterday and saw the solder joints from the switches on the keyboard board) and I strongly believe that HX-10 keyboard have similar construction. However, most computers don't: the Philips VG8020/00 (which is a well designed and constructed MSX in oposition to the VG8020/20 which have poor and cheap single layer "made of cardboard" PCB and PSU) has a simple twin-plastic membrane keyboard which is the cheapest and "worst" type of keyboard ever made.

Other keyboard designs have a plastic membrane and a PCB construction (lines on membrane and columns on PCB or vice-versa) or rubber conductive membrane (or even individual pads) over PCB (all keyboard traces are on PCB, the conductive rubber just make the connection between each line/column). The latter has a better feel, as the rubber membrane/pads have some tactile feedback (it has - like the individual tactile switches - almost the same feel from a clicky switch, but does not click thou).

That said (yes, I saw every keyboard type I mentioned on MSX) you most likely have a dirty (EDIT: with dust, grease from sweat and/or oxidization) or bad membrane (EDIT: oxidized or scratched conductive paint)/conductive rubber (EDIT: dirty from previous possible causes) instead of a bad switch (EDIT: which could also have dirty contacts) or a broken solder joint.

EDIT: about cleaning contacts with alcohol, just make sure you use isopropanol/isopropyl alcohol, as regular cleaning alcohol contains a small amount of other chemicals that isn't suitable for electrical contacts.

About contact cleaner, if you have a proper contact cleaner you're good to go. But some people thinks that "spraying-type" lubrificant oil and similar formulas (like the well-know WD-40) are suitable for contact cleaning. (this is common belief here in Brazil, I don't know if it is common where you live). Well, let me say this: DON'T DO THAT OR YOU MAY RUIN YOUR COMPUTER FOR GOOD! Or, at least, you could end with a oily contact that will work for a few days and then will stop working again because dust will stick to the oil and the contact will be dirty again in no time.

By Wild_Penguin

Hero (638)

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27-05-2016, 22:26

What valenca says about contact cleaners is true (and rest of the post, too!). I have heard that there are some contact cleaners that are not meant for more delicate electronics, and some for larger machinery - so make sure you got the right type. I'm not a mechanic (or anything of the sort), but I believe the wrong type has sume lubricants (while still being called "contact spray"!), and is meant for large sliding electric contacts /switches you may find in automotives and other large machinery... the contact spray I have, does not leave any residue after it dries away (in 30-120 seconds depending on how much I've sprayed). If your spray does leave any visible /tangible residue, I wouldn't use it on any kind of PCBs.

If / when you open the keyboard, take pictures! That way we all can see what kind of keyboard does the FC-200 have Smile

By MichelM

Expert (80)

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28-05-2016, 00:23

I pulled out the keys - It's the "L" key in the middle. I do believe the keys are somewhat different than the HX10. As you can see in the pictures there is something on the board (black) which appears to be glued on there, but there's nothing under the keys itself - the keys are directly attached to the board. I looked underneath, but the solder looks okay to me. I do believe I have the correct contact spray, so I'll give that a try.

By Wild_Penguin

Hero (638)

Wild_Penguin's picture

28-05-2016, 10:02

So you have individual mechanical switches on your FC-200. We can say for certain, that it is absolutely of no use to blow canned air or contact spray on the switches without opening them up (save for dislodging some breadcrumbs / dust / etc. that could be stuck between the key keycap and PCB; but that should come quite easily off by just turning the keyboard upside down and shaking it).

I am not familiar with that particular switch type, but from these pictures is looks like you need to desolder a mechanism before you have any chance of opening one up, since (it looks like) the metal lid is directly connected to the soldering leads/legs/whateveryoucallem (I can not say for certain from these angles). If you are going to do that, be careful when opening - you need to do some guesswork (unless you can find someone who has opened this mechanism before or an exploded view or something), and (I suppose) it is always possible you are going to break something beyond repair while opening the mechanism! But, if it is already broken, there is not much to loose...

As said before, checking the solderings should be quite easy, and if they are faulty, they should be fixed before dismantling a key.

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