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My Toshiba T1100 Repair

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    #16
    I posted an answer here a week ago, still waiting for approval ? Seriously ?

    Comment


      #17
      Refer to the information at [here], which provides some detail into the (initial) startup sequence of an IBM PC. Of course, the T1100 will be different in some respects (e.g. how RESET is generated, etc.), but in essence, the T1100 will be doing similar.

      The oscilloscope screen capture at [here] shows that on my good T1100, the approximate delay between apparent +5V stability (top trace) and the CPU's RESET pin being taken low, is about 150 ms. Several measurements done; 150 ms approximate is consistent.

      The oscilloscope screen capture at [here] shows that on my good T1100, activity on the BIOS ROM's /CE pin (pin 20) (bottom trace) starts about 2 us after RESET on the CPU is taken low.

      Comment


        #18
        Hey Modem7,

        Well I've made some progress in some areas, and went back in others
        Summary

        - Now boot reliably (!)
        - Now spits out a "NO KEYBOARD" error whatever I do. Yes, I'm close to toss it thru the window.

        In details (mostly if it helps someone in the future than for me)

        I've recapped the entire screen. The old caps where within specs, but as I had a transient speak of current that only appeared when plugging in the screen, I thought, hey why not.

        Original caps



        New caps (panasonic)




        I've also recapped the entire powerstage (electrolytics) + a few tantalums

        Original ;


        New caps (smaller, technology advanced in 34 years)



        All of this was... Quite useless
        I've tested everything I desoldered and they were all within specs. Those Nippon Chemi-Con are just immortal.
        I've tested the power supply after recap and it displays marginally better ripple.

        Again I was pretty sure from my measurements caps where not the issue, but well I wanted to try anyway.

        Comment


          #19
          What seemed to be the root cause of my boot issue was, as I suspected, the bus controller.

          It probably suffered more thna I thought from nicd battery spills. These were very small, but here's what I learned
          - The liquid that spills it actually NaOH so highly corrosive.
          - If you neutralize it with vinager, which I did, you end up with sticky salts residues that conduct electricity even more than the original spills

          SO clearly I wouldn't recommend at all to neutralize with vinegar on a motherboard, as the resulting salts made it even worse.

          I've got back my booting after washing the entire motherboard under the shower with soap + rinse with 99% IPA. Half a dozen of times, with little brushes.

          Now i'm with

          NO KEYBOARD

          Whatever I do.

          Comment


            #20
            I've probed a bit with the oscilloscope on the keyboard controller
            (or what appears to be a 8 Bit microcontroller used, probably, as a keyboard controller ; a 80c49AF-6) - lower right of the board

            The thing gets a 4Mhz clock in its XTAL pins (around 33/34 iirc) - top left pins.
            Gets a proper RESET (high). top left pins as well

            Nothing seems to happen further than that.
            Either this is the most silent microcontroller on earth, or it's dead.
            Not sure where it gets it's code from. Not sure what could make it not work ( broken trace, broken pin ? )

            But I'm a bit lost with my "no keyboard" error ( of course the flat cable is connected )
            I checked the keyboard board and it seems fine. Switches are fine. Flat cable is fine and tested a dozen of times. Solder joint on flat cable & keybaord board are fine.

            I believe either the 80c49 fails to start for some reason, or it's just broken.
            WIthout a schematic it's really not easy.
            I need a real hobby

            Comment


              #21
              I'm having a similar problem with memory on my Compaq Portable III. :P (Plus a busted backplane connector that I haven't found a replacement for yet.)

              Did you check the keyboard encoder chip?

              Comment


                #22
                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.
                Last edited by CedsRepair; November 20, 2020, 07:43 AM.

                Comment


                  #23
                  Originally posted by CedsRepair View Post
                  I posted an answer here a week ago, still waiting for approval
                  Quite a few posts have appeared.

                  Originally posted by CedsRepair View Post
                  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.

                  Originally posted by CedsRepair View Post
                  ... 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.

                  Originally posted by CedsRepair View Post
                  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.

                  Originally posted by CedsRepair View Post
                  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.

                  Originally posted by CedsRepair View Post
                  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).

                  Originally posted by CedsRepair View Post
                  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.

                  Comment


                    #24
                    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.
                    Last edited by CedsRepair; November 23, 2020, 02:17 AM.

                    Comment


                      #25
                      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.

                      Comment


                        #26
                        Originally posted by CedsRepair View Post
                        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.

                        Originally posted by CedsRepair View Post
                        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.

                        Originally posted by CedsRepair View Post
                        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".

                        Originally posted by CedsRepair View Post
                        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 ?

                        Comment


                          #27
                          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...

                          Comment


                            #28
                            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.
                            Last edited by CedsRepair; December 5, 2020, 04:55 AM.

                            Comment


                              #29
                              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.
                              "If it ain't broke, fix it until it is"

                              Comment


                                #30
                                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.

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