My Toshiba T1100 Repair

[T-Squared]

I'm having a similar problem with memory on my Compaq Portable III. (Plus a busted backplane connector that I haven't found a replacement for yet.)

Did you check the keyboard encoder chip?

 

[CedsRepairs]

I'm not really experienced in vintage repairs, and I think I started it with a complicated one
( or maybe they are all frustrating and complicated )

I have no schematic but it seems a 80C49 is used as kinda "keyboard controller". ( 8048 seems to have been standard back in the day for XT )

All the signals I can see are VCC, RESET and SS that are all high. Clock is at 4,77Mhz and seems to be external.

So the thing should do something I guess but it does nothing at all. No signal are moving on the keyboard connector (a flat cable) so i guess nothing is wrong on the keyboard. the thing doesn't even try to communicate with the keyboard as far as I can see.

Either something prevents the 80C49 from "booting" or it's just dead.
Any advice appreciated



The "keybaord" part seems alll the lower right corner. (logic + chip)
The black flatflex connector beeing the keybaord connector.
Chip in the lower/right beeing the 80c49 8bit microcontroller.

I've now a perfectly "working" T1100 ( the "no keyboard" error beeps, but doesn't prevent it from booting), now boots all the time, reads floppies, boot dos 2.11
But I cannot do anything as "no keyboard"

Hyper frustrating as I revived this from the dead, recap, re-battery, ultra-clean it, even repaired the "b" key, and I feel se close to have it 100% working.
And so far at the same time.

 

[modem7]

I posted an answer here a week ago, still waiting for approval

Quite a few posts have appeared.

I have no schematic but it seems a 80C49 is used as kinda "keyboard controller".

For readers, the T1100 maintenance manual indicates that the 80C49 is in fact being used as a keyboard controller.

... the "no keyboard" error beeps, but doesn't prevent it from booting ...

On my good T1100, I hear a single beep at the end of the power-on self test (POST), which seems to be a normal thing for POST's to do.

When I look in the T1100 maintenance manual at the activities that occur during the 'Power-On Diagnostics', one of the later tests is a 'Keyboard Attachment Test' (page 2-10). Unlike the early tests, there is no code sent to the printer port. Instead, the manual indicates that "N0 KEYBOARD" will appear on-screen, with no accompanying beep.

So the beep you are hearing must be the end-of-POST beep.

Now spits out a "NO KEYBOARD" error whatever I do.

On my good T1100, if I remove the keyboard's flat ribbon cable from the motherboard's keyboard connector, then power on the T1100, I still only hear a single beep at the end of the POST. There is no "NO KEYBOARD" error (or any error) on the screen, suggesting that the Keyboard Attachment Test is indeed probably interacting with the 80C49.

Not sure where it gets it's code from

On reading the simple description of the EA pin (pin 25), I expected that the EA pin of the 80C49 would be tied either to ground or Vcc, but my logic probe shows constant activity, suggesting that in the T1100, the 80C49 is reading code from ROM off the chip.

The thing gets a 4Mhz clock in its XTAL pins (around 33/34 iirc) - top left pins.

19 and 20. I only used a logic probe, but it too showed actvity (as expected).

Nothing seems to happen further than that.
Either this is the most silent microcontroller on earth, or it's dead.

In the datasheet, a description of the ALE pin (an output) is, "The signal occurs once during each cycle and is useful as a clock output."
Sure enough, on my functioning 80C49, my logic probe shows constant (never-ending) activity out of the ALE pin.

Yes, a circuit diagram would be good.

A bad input ?

My /PS pin (power saving)(pin 1) measures 0V but does not show as LOW on my logic probe. No continuity to ground. Unconnected?

Getting back to the EA pin, an input. You are not seeing what I am. Maybe work on that.

 

[CedsRepairs]

Thanks that is really helpful, as I can compare with my situation

It's likely this problem is somehow related to the bus controller as well; as this thing has been the only problem of my T1100 so far.

Some wrong info is either received or sent from the 80C49 that makes this NO KEYBOARD error (and the controller doing nothing).

If I can solve that, the thing would be as good as new again, but it's not easy to solve.

 

[CedsRepairs]

I have zero activity on the EA pin

I don't understand what could be wrong

Ray, just to confirm : you're saying that if you remove the flat cable from the motherboard, your T1100 does not say "NO KEYBOARD" ?

On mine, either that controller is dead and my T1100 is worthless, or something prevents it from starting (hopefully that's it)

When I switch power, I have zero activity on the controller, it receives a clock, /reset is high, it should be doing something but does nothing.

The fact that is a multi layered board does not help, as there are tarces I simply can't follow.

 

[modem7]

Ray, just to confirm : you're saying that if you remove the flat cable from the motherboard, your T1100 does not say "NO KEYBOARD" ?

Correct. "NO KEYBOARD" does not appear.
And I confirmed it again, today.

The fact that is a multi layered board does not help, as there are traces I simply can't follow.

What I do is put my multimeter into continuity mode (i.e. beep at low ohms), put one probe on the reference pin, then run the second probe over the pins of all components (i.e. not only the chips), listening out for a beep from the multimeter. In continuity mode, my multimeter beeps at anything under 100 ohms, and so when I hear the beep, I check to see that the ohms shown is zero or up to a few ohms.

I don't understand what could be wrong

If a similar problem existed on my T1100's system board, then I would be 'in the same boat'. Because without the faulty bit being visually faulty, I would need the T1100's circuit diagrams, source code, and a good understanding of how it all 'works in concert'.

Many hours would be required to create a circuit diagram of the T1100's system board. And some disassembly of the system board's BIOS to see what triggers the POST to display "NO KEYBOARD".

On mine, either that controller is dead and my T1100 is worthless, or something prevents it from starting (hopefully that's it)

Wanting to see the KEYBOARD ERROR message for myself, I tried some experiments.

With the keyboard connected, I held down the H key whilst powering up the T1100. Odd was that the RAM test only went as far as 80 KB (well, on-screen anyway). But no KEYBOARD ERROR message. Multiple H keys appeared to have been registered because the 'Place system disk in drive. Press any key when ready.' sequence ran for quite a few iterations.

Okay, so I will 'disable' the 80C49. I tied the 80C49's /RESET pin (22) to ground. No KEYBOARD ERROR message during POST !!!

Confirmed that the 80C49's VSS pin is connected to the ground running about the system board. And VCC is tied to +5V. So it wasn't a case of incorrect ground being used.

- Instead, short circuited the 80C49's two XTAL pins. No KEYBOARD ERROR message during POST.
- Instead, tied the 80C49's EA pin to ground. No KEYBOARD ERROR message during POST.
- Instead, tied the 80C49's EA pin to +5V. No KEYBOARD ERROR message during POST.

The above suggests that the keyboard test in the POST is not communicating with the 80C49 !!!

I went back to tying the 80C49's /RESET pin to ground. I then powered on the T1100. Again, no KEYBOARD ERROR message. And pressing a key on the keyboard works (specifically, at the 'Place system disk in drive. Press any key when ready.' message, pressing a key triggers another attempted read of the diskette drive).

So, with Toshiba indicating that the 80C49 is a keyboard controller in the T1100, how is it that disabling the 80C49 still allows the keyboard to work ?

Are Toshiba lying to us by indicating that the 80C49 is a keyboard controller in the T1100 ?

 

[CedsRepairs]

Well there are direct connections (thru inverse logic gates just left/up of it) from the keybaord flat cable to that chip
So it is for sure the keyboard controller

However it is clearly not starting up for some unknown reason in my board...

 

[CedsRepairs]

The strange chip marked "DL1E" right to the CGROM seems to be involved in this "no keyboard" error message

It's in direct contact with the pc speaker itself (very long trace), what's even weirder is that it seems to produce the beeping sound (together with "NO KEYBOARD") itself

From what I can see (trace), basically only the CPU AND this myserious chip can make sounds on the pc speaker.

I wasn't able to find any data sheet on that thing. No surrounding passives apart from a resistor - so this must be mostly a logic/comparator thing, that's as much as I can tell. maybe a partially unused opamp.

 

[rimmeruk]

My bet is the keyboard ribbon cable damaged or the keyboard is faulty. That part of the board looks very clean and undamaged
from the photo so unless you have accendently shorted something out whilst repairing the keyboard I can't see any of the IC's
being faulty. Only way to find out is to try another cable and keyboard. You can buy those flat ribbon cables in many sizes off ebay.

 

[CedsRepairs]

Just to post an update on this

In other not to spend my last years on earth fixing a T1100 I've bought another one, and will keep the "no keyboard" one for spare parts. My diagnostic (or lack of) so far is that either the 80C49 is dead, or some inner copper trace linking it to the bus controller has been corroded by nicd leak (I can't fix that without a schematic)

The new one I got is functionnal, and had the ram extension and the original power brick.
By the way, someone posted here that the manual of the T1100 states that the power brick is 20V (which is true : it is indeed written in the manual)
But I can confirm the T1100 powerbrick is 18V, not 20V, photo available if that is necessary.

All in all I've got a T1100 with many add-ons, as I've now combined :
- The rare modem/RS232 expansion card (the only picture of that thing on the whole internet is mine )
- The 512K RAM extension ( Modem7 has one too )
- The original powerbrick ( I don't think these are common )
- The orignal case
- And my own "remade" NiCD battery
+ another T1100 for spares in case anything dies ( floppy, screen, etc)

In a whole package.

 

[modem7]

The new one I got is functional, ...

Congratulations.

By the way, someone posted here that the manual of the T1100 states that the power brick is 20V (which is true : it is indeed written in the manual)
But I can confirm the T1100 powerbrick is 18V, not 20V, photo available if that is necessary.

Photo not needed. There is a photo already (in a link) at [here].

 

[Kangurudy]

Well, a bit late as you already decided to stop with the repair and bought another T1100, but maybe some background information on this, that could be worthful for others (or in future for you too...)

The 80C49 is an improved version of the 8048/49 microcontroller, which was used in the IBM-AT and following generations of PC compatible computers.
As the T1100 is a XT-Class computer, it is a bit surprising to find that solution inside.

But to be compatible to IBM Toshiba had to follow IBM at least at the boundaries (interfaces) of each unit. So you can be almost sure, that the 80C49 is programmed in a way that is compatible at the register-level to IBM. As IBM had NO intelligent keyboard-Controller on the PC and XT generation, the interface is rather simple. Details e.g. here: http://minuszerodegrees.net/5160/keyboard/5160_keyboard_interface.png

As in contrast to normal desktop computer keyboard is integrated inside T1100, the 80C49 makes basically the job of the controller INSIDE the separate keyboard of normal computers! The output is a serial stream which is clocked into a latch and then read in parallel form by the PCs processor. (using 8255 PIO in XT class).

So i would compare the output of a XT-class keyboard (there are simple converters on the market (and also for DIY) to connect even PS/2 style AT-Keyboards to XT machines) with the behaviour of the "unknown" Pins of the 80C49 ( all pins used for scanning the key matrix are easy to find out and are out of race for this part...), starting with the pins which are used inside the Keyboards (find an elder one and you will find 8049 or similiar inside too!) One line is simply some kind of clock, which starts after a signalisation from the keyboard, that new data is available, the other pin is serial data. (the starting signal is part of Data which normally is high-active but is tied to GND if new keypress-data is available) Clock is generated by the T1100, not the 80C49!

Then cut through the traces from the 80C49 (or even unsolder the 80C49) and connect a XT Keyboard-Connector instead. Finished!

With this infos you can at least connect an external XT type keyboard already. To use the internal one, you would have to programm a 80C49 (to be able to solder it in without any change of Pins...) or at least any small controller like PIC18F or ATMEGA to scan the keymatrix and send the matching keycodes to the T1100 using a serial slave register, available as "SPI" in almost any controller today. The table of Scancodes is found again in IBM documentation for XT (IBM 5160).

There is a small chance (as AT was already out at the time Toshiba introduced the T1100), that T1100 even has the improved AT-Interface (which you would find out while watching the signaling on the working one as it is slightly different from XT), but that would make it even more simple: there are thousands of different Computers outside, that have such 80C4x as an AT-Keyboard-controller onboard, some notebooks (like Sanyo NB17/18 -also sold as Commodore LT286/LT386sx) even had the same smd version there... *) So you can use these chips to connect an external AT Keyboard at least. If you want to use the internal one, you can -like above- program your own code (IBMs Code for AT Keyboard-controller is available on the internet as a template) or reuse the chip found inside any external keyboard and adopt the keyswitch-matrix to match the Toshiba one...

Sounds like big work, but is rather uncomplicated, especially now that you own a working one making it easy to find out the function of every pin. IBMs hardware manuals for XT and AT will be a great help for that too...

*) these notebooks had TWO Keyboardcontrollers on board: the one which normally sits inside the external keyboard and the one which always sits as part of the chipset on the mainboard of any PC-AT or later computer. This was made to be 100% compatible and also this allows for an easy connection of external keyboards alternatively to the internal one. (but this feature was not used in these models for whatever reason...)

Good Luck!

Rudy ;-)

 

[ajacocks]

Kangurudy thanks for the detailed write-up, and welcome to the forum!

- Alex