Author Topic: TI-83+ Repair. Powers to black screen?  (Read 373 times)

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Offline SirAlucard

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TI-83+ Repair. Powers to black screen?
« on: March 03, 2018, 06:26:52 am »
Hey guys, so I'm in the process of trying to figure out what is wrong with my TI-83+, my brother ended up giving it back to me a long time ago broken and in this state, and just now I'm getting around to trying to fix it. I do have an identical board to compare to it however I'm having trouble finding a datasheet for the CPU. Which is a Inventec 6SI837, I'm trying to figure out what a pin is suppose to be doing, and where it leads. As I'm noticing that on my DEL button, (at least this is the one I've been watching) it tends to climb in voltage, up to .5mv then releases the voltage. Now it shouldn't be doing this, as with my working chip there is no voltage on that point. The other part of the pad reads 3.3v no problem. So it has to be stuck somewhere. I've gotten the calculator to boot shortly once, but I'm not really sure what I did as it's not repeatable.

Any suggestions and help would be fantastic!

EDIT: I forgot to mention, that I did indeed check to make sure that it's not the contrast setting. I also checked the wiring for the LCD to make sure that everything was connected, as these are known to get crimps in them then suddenly not work. I had to bodge some wires to fix a few points, but it is all connected and the LCD does indeed work fine.
« Last Edit: March 03, 2018, 06:38:45 am by SirAlucard »
 

Offline 0xdeadbeef

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Re: TI-83+ Repair. Powers to black screen?
« Reply #1 on: March 03, 2018, 06:34:25 am »
Dunno if it's the same for the TI-83+, but I recently tried to reactivate my good old Ti-85. When I tried to power it up, it just showed a blank screen so I assumed it was dead.
Well, after some fiddling around I faintly remember that there was a contrast setting and the display tended to use the lowest contrast after battery change.
So indeed, by pressing Shift+Up quite a few times to increase the contrast, the display came back in its full low-contrast-early-90s glory.
Trying is the first step towards failure - Homer J. Simpson
 

Offline SirAlucard

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Re: TI-83+ Repair. Powers to black screen?
« Reply #2 on: March 03, 2018, 06:36:59 am »
Dunno if it's the same for the TI-83+, but I recently tried to reactivate my good old Ti-85. When I tried to power it up, it just showed a blank screen so I assumed it was dead.
Well, after some fiddling around I faintly remember that there was a contrast setting and the display tended to use the lowest contrast after battery change.
So indeed, by pressing Shift+Up quite a few times to increase the contrast, the display came back in its full low-contrast-early-90s glory.

Thanks for the reply, I actually forgot to put that into my original post, yea I've already made sure it wasn't the contrast setting. It's funny when I was writing the post I was saying to myself to make sure to put that in cause for sure someone will point that out immediately. Go figure I ended up forgetting it. :)
 

Offline SirAlucard

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Re: TI-83+ Repair. Powers to black screen?
« Reply #3 on: March 05, 2018, 03:48:37 am »
After some more probing around, I found area of the board that has a significant voltage difference. The majority of the board on the working unit is 3.5v, while the non working board is 3.29, I figured it was just 3.3v. However one area I found on the non working board is around 1.7v when the working board is 3.5v, so there definitely has to be something going on there. Strangely enough too, I was probing the button traces and one area of the board specifically the up/down/left/right area, which I imagine is all attached, changes voltage much more rapidly than the rest of the traces. I don't really know what that means, but I thought it was interesting.

Is there really no datasheet for these boards/chips? I get TI wants to protect their overpriced calculators but come on. Seriously tho there's no reason why a ti-83+ should still be nearly $100, when their newest calculators are around the same price.
 


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