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Need Troubleshooting Advice - Stuck on Press any key screen


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I recently bought a TI-99/4a on Ebay. It was a single owner machine with all of the original manuals, packaging, and cables. It is all in beautiful condition. It looks like it is brand new. I have always wanted one since my cousin showed me his back in 1981 or so. I had a TRS-80 Model 1 at the time. He showed me the sprite capabilities and the voice synthesizer. I was envious!

 

The problem is that my TI-99/4a doesn't work. It powers up and shows the press any key screen, but when I press any key it doesn't do anything.

 

I have a Master's degree in Computer Science and 30 years of experience. I am a device programmer. I mostly program, but I do some module level hookups and electrical work. I don't do a lot of board level work, but I have used a multimeter, oscilloscope, and soldering iron. I found a technical manual on the Internet that included a schematic.

 

I am looking for any advice before I crack the case. Has anyone seen this symptom before? What is the most probably cause? Is it possible to get replacement parts? Is there anything I can reseat? Could something have just come loose in shipping. That kind of thing. Any advice would be better than what I have now. I would really love to have a working unit so I could play around with Basic programming and show my daughter what a real beginners computer should look like.

 

Thanks!

Sean Lane Fuller

 

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I would check the keyboard first. Pop the cap off of one of the keys. If you have a plus-shaped post under there, you have a Mitsumi membrane keyboard. These often do what you are describing (only some of the the beige keyboards have the membranes--and none of the black ones). If you have the square pit with a pair of gold fingers in it--this is good. These keyboards can be carefully cleaned with an alcohol swab. If you have the Mitsumi keyboard, the best thing to do is to replace it with one of the other types (they all work here). It is only a single connector between keyboard and motherboard--and very easy to remove, as it was designed to be replaceable. The keyboards show up on eBay pretty regularly--for reasonable to outrageous prices. If you are having this problem with one of the non-Mitsumi types, you may have one or more broken wires in the connector. The connector and the pins are readily available on eBay too, so you can rebuild one to get it to work. Anything else would be a problem on the motherboard--but I'd start with the keyboard. . .

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+1 on a bad keyboard as prime suspect. If you have a joystick, the Fire button may act like an F or J key. You'd still be dead in the water, but able to get past the Press any key screen.

 

If you have the case opened, pretty easy to jumper some of the keyboard pins to check for the motherboard accepting anything. Trace out which pins are for the 1 or 2 key to get you to Basic or whatever module is installed.

 

-Ed

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If you have a plus-shaped post under there, you have a Mitsumi membrane keyboard. These often do what you are describing (only some of the the beige keyboards have the membranes--and none of the black ones).

 

You mean like the black/silver one of mine? :)

 

Too bad I'm getting this contact issues right now, after I built this USB interface. It also seems to me as if the membrane get worse now that I continue typing on it.

 

(Yes, ugly dirty keys ... I should try to pop them off, but it was already difficult to get one off, and I'm afraid to break one of those posts.)

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Guessing it's a beige model? The Mitsumi keyboards suck. They just suck. There are beige keyboards that are not mitsumi (and therefore do not suck). You can tell them in the ebay auctions by the green circuit board for the keyboard, visible through the air slots on the bottom. Brown circuitboard=suck; green circuitboard=good.

 

Darryl

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(see also Facebook TI99ers, with pictures).

Greg McGrill has helped me out to explain it and I exchanged it, all works fine!

 

In short -- if you see a brown (= Mitsumi, backplate of the keyboard) that is called "mylar" material

(I call it a "my liar" keyboard as "lies" and it does not work, especially after years in storage!

(but it actually worked good 20+ years ago, what you also can try it keep pressing the keys,

suddenly keystrokes start to work I noticed. If you have a 3.5 year old kid, he can help you with this

pressing the keys 100 times :-)

 

 

replace it with a green backplate one (switched typed of keyboard).

 

You can find keyboards at Ebay (make sure that is has the green backplate) and not brown/mylar

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^^Agreed with schmitzi. My #1 console has this keyboard.

 

That one you have, michael, is unlike any of my consoles.... I have one membrane, the rest are the green board.

 

But for some reason, there seems to be variation even amongst the green ones... I am no expert, but several of my keyboards do not feel the same... Even the newer TIs seem to feel different in key pop.

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Ralf, if you have that many consoles as you told me, could you possibly check whether there is a correlation between the key labels (notably the "1" key) and the technical implementation. That is, maybe we have differences between consoles manufactured at the various sites.

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Mizapf - you have one of the good ones. In my experience there are at least two types of keys with distinct switches - the one with the two contacts others are mentioning, and the ones with sealed buttons like yours. The fact that you see individual switches coming down to the PCB is the giveaway.

 

The crappy ones we're talking about are similar to the TI joysticks - they simply have printed contacts on two layers of film under the keys. It seems over time the contacts have oxidized or degraded, I'm not sure which, and the keys tend not to respond well, or at all.

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Ah, OK. The problem why I brought up that version is that some of the keys almost don't work anymore. The O key, for instance, only reacts when I exert hard pressure on it, with some sideway moving. The Enter key has the same problem, but seems to have recovered. So I thought this is a low-quality switch type.

 

Thus we have at least three versions of keyboards, as it seems.

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just to figure out again, I think that the keyboards where you can see the golden "clamps"/contacts, in this square-box, are the very best.

(like the one I have as spare) they are very comfortable and responsive, and have a nice "click"-experience

 

I made some pics now, hope that is what you wanted

 

 

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(just for fun)

Now the other question is, did TI release any "Azerty" type of keyboards? (probably not, because of the internals? mapping of the keyboard?)

 

 

The TI-99/4F has a "clavier Azerty": http://www.ti99.com/ti994f.htm

(Azerty: these are typically used as Keyboard in Belgium and France ... I run against it last April again visiting family in Belgium, fixing their PC, every time pressing the "wrong" keys

 

AZERTY:

https://www.google.com/search?q=azerty&tbm=isch&tbo=u&source=univ&sa=X&ei=v3liVaWIBciiuQTI54HYBw&ved=0CEMQsAQ&biw=1366&bih=633

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Ah, OK. The problem why I brought up that version is that some of the keys almost don't work anymore. The O key, for instance, only reacts when I exert hard pressure on it, with some sideway moving. The Enter key has the same problem, but seems to have recovered. So I thought this is a low-quality switch type.

 

Thus we have at least three versions of keyboards, as it seems.

 

yeah. In my experience, that keyboard will come back with use, banging the key for a while will move the dirt aside (with corresponding increase in wear, but that's what I did as a kid ;) ). The suggests that tuner cleaner (maybe WD40?) would help, too, if you could get it inside the key alongside the stem -- but I haven't tried that. Kind of experimental at this point, but that keyboard has real metal contacts and will be cleanable. :)

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The only localized keyboards done for the TI were used in Argentina. They added the N with a Tilde on top on some of their keyboards (I have one, but not the motherboard that it needs to recognize the change). Eventually I'll have one of those too. . .

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