From Newsgroup: comp.sys.tandy

My Tandy 1000ex boots up great, outputs perfect video and audio, reads my 5.25'' floppies, and generally seems clean upon inspection, however, there seems to be some issue with the key input.
For example, in Boulder dash, the character is constantly moving left, and in other text fields, a constant shift leftward is present, as if the left arrow key is constantly being pressed. I disconnected the keyboard and the issue remained, meaning the Tandy thinks a key is always pressed, regardless of the presence of the keyboard.
I ordered a joystick adapter hoping to play without needing to worry about the arrow keys at all, but I'm now wondering if the input of the joystick totally overrides any previously present input (would the joystick cause the Tandy to disregard the constant left input?).
Regardless, If anyone has any information as to what problem my Tandy 1000ex is having or how to visually identify the problem on the motherboard it would be great to hear it.
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From Newsgroup: comp.sys.tandy

On Thursday, 7 October 2021 at 17:44:50 UTC-7, butter...@gmail.com wrote:

My Tandy 1000ex boots up great, outputs perfect video and audio, reads my 5.25'' floppies, and generally seems clean upon inspection, however, there seems to be some issue with the key input.

For example, in Boulder dash, the character is constantly moving left, and in other text fields, a constant shift leftward is present, as if the left arrow key is constantly being pressed. I disconnected the keyboard and the issue remained, meaning the Tandy thinks a key is always pressed, regardless of the presence of the keyboard.

I ordered a joystick adapter hoping to play without needing to worry about the arrow keys at all, but I'm now wondering if the input of the joystick totally overrides any previously present input (would the joystick cause the Tandy to disregard the constant left input?).

Regardless, If anyone has any information as to what problem my Tandy 1000ex is having or how to visually identify the problem on the motherboard it would be great to hear it.

You can find the technical reference manual for the EX here: ftp://ftp.oldskool.org/pub/tvdog/tandy1000/documents/extech.zip
Page 82 has the schematics for the keyboard controller. Check to see if anything on the motherboard might be corroded or shorting around the 8048 microcontroller (U6, should be right next to the keyboard headers).
If the rest of the keys work, then I don't find it likely that the microcontroller itself is hooped, but there's always the possibility.
On pages 134 & 135 are the keyboard mapping. Left arrow is B13 on the matrix, which corresponds to shorting pin 4 on J1 with pin 19 on J2. Problem is that these numbers correspond with the schematic for the mylar circuit in the keyboard, and the motherboard uses different numbers, so you'll have to figure out yourself which pins on the 8048 those correspond with.
Hope that can get you started. Front and back pictures of the motherboard may help. I've got an HX, but the layout of the motherboard is a bit different from the EX, so I'm just going off what's in the tech reference manual.
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From Newsgroup: comp.sys.tandy

So i need to dismantle the keyboard and follow the circuit from the left arrow key all the way through the ribbon cable header into the 8048 and look for a break?

Also, nothing appeared corroded on the keyboard in any way and the 8048 microcontroller looked visually fine.

Will be getting pictures soon.
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From Newsgroup: comp.sys.tandy

On Sun, 10 Oct 2021 15:12:04 -0700 (PDT), "Lt. Mark"
<butternubs92@gmail.com> declaimed the following:

So i need to dismantle the keyboard and follow the circuit from the left arrow key all the way through the ribbon cable header into the 8048 and look for a break?

Presuming a common matrix-scan keyboard, there are two wires connecting to each key (row/column) one wire (at a time, say, ROW) is driven by the keyboard processor, while the other (COL) wires are scanned to see which is active. The intersection of row<>col determines the key that is pressed.

Holding down three keys (in the proper configuration) will result in a phantom fourth key being registered.

I think I would be looking for a shorted line (row<>col), not a break. This might require a high-impedance oscilloscope these days -- though if
the system is 5V compatible (and it appears old enough to be 5V and slower clock speeds) an old fashioned logic probe might suffice (wow... still available as a kit under a different maker's name https://www.amazon.com/Elenco-Logic-Solder-SOLDERING-REQUIRED/dp/B0002EALLM/ref=sr_1_14?dchild=1&keywords=logic+probe&qid=1633969332&sr=8-14
mine goes back to the early 80, under the CSC brand as I recall)
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From Newsgroup: comp.sys.tandy

On Sunday, 10 October 2021 at 15:12:05 UTC-7, butter...@gmail.com wrote:

So i need to dismantle the keyboard and follow the circuit from the left arrow key all the way through the ribbon cable header into the 8048 and look for a break?

Also, nothing appeared corroded on the keyboard in any way and the 8048 microcontroller looked visually fine.

Will be getting pictures soon.

I don't think you'd find a break necessarily, but something that looks like it might be shorting or sticking. Perhaps something stuck under the keyboard before the mylar membrane that could be causing it to contact. I'm surprised it isn't beeping at you constantly from a sticky key. Also check to see that nothing is shorting beneath the motherboard around that 8048 and J3/J4 and J7.
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From Newsgroup: comp.sys.tandy

On Sunday, October 10, 2021 at 6:12:05 PM UTC-4, butter...@gmail.com wrote:

So i need to dismantle the keyboard and follow the circuit from the left arrow key all the way through the ribbon cable header into the 8048 and look for a break?

Also, nothing appeared corroded on the keyboard in any way and the 8048 microcontroller looked visually fine.

Will be getting pictures soon.

But he said that the problem is still there even if the keyboard is unplugged so how is cleaning the keyboard going to help?
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From Newsgroup: comp.sys.tandy

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From Newsgroup: comp.sys.tandy

How do i completely remove the motherboard? It seems attached to the metal sheet via the screws around the monitor port, and the screws look tack welded together. (on both sides of the part that says "BURNDY")
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From Newsgroup: comp.sys.tandy

On Wednesday, 13 October 2021 at 02:17:29 UTC-7, butter...@gmail.com wrote:

How do i completely remove the motherboard? It seems attached to the metal sheet via the screws around the monitor port, and the screws look tack welded together. (on both sides of the part that says "BURNDY")

You ought to be able to just unscrew the DB-9 connector retaining nuts that hold it to the metal shield, if they've got the usual hex-shape. The nuts on top of the DB-9 are to reinforce it to the motherboard. Be careful of the volume knob, it might snag.
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