XT clone weird keyboard issue

[hbsoftware]

Hi everyone
i recently accquired a nice turbo xt clone with a NEC D5126 20mb mfm drive
the computer boots fine after cleaning the mainboard , reseating all the ics and deoxit the sockets
the hard disk works and sounds healthy and i tested it completely on other pc too
but i am having a problem with the keyboard
the keyboard seems to work fine because when i press too much times any key the speaker beeps but i cannot type anything on DOS
the only key combination that seems to work is ctrl+break. i cannot even type the date and time, i have to press ctr break to skip that and then when i am at the c> prompt i cannot do anything other than making the speaker beep
i am using a good known keyboard from a 5160 xt but the weirdest part is that if i plug in an AT keyboard the result is the same, speaker beeps and ctrl break works , caps scroll and num lock leds light up but nothing else works, i am surprised that ctrl break works with an AT keyboard...??????

now another thing that seems inoperative are the dip switches...no matter how i set the memory or anything else it doesnt seem to change anything for example dip switch 1 when set to on should throw the computer on a booting loop and it doesnt do that...memory is always 640kb no matter how i set the dips for the memory...
i did a little digging and i know that U37 a D8255AC-5 chip controls the keyboard , the speaker and the dip switches... the speaker also makes a funny click at startup almost like it wanted to beep but stopped...it beeps fine when i press keys though

as far as test gear i am limited because i mostly work with analog electronics (i repair vacuum tube equipment mostly tvs) but i have the basics , multimeter , i can solder and desolder ics and the fastest scope i have is 20mhz (lol)

if i order a new d8255ac is it plug and play or it needs to be programmed like an eprom? sorry if it sounds like a dumb question

anyone has any idea what can i test or what is likely to be wrong here? any help would be massively appreciated
i am sorry for any spelling errors, i am not a native English speaker
thank you

 

[hbsoftware]

ok so after fighting this issue for quite some time , dessoldering some 74LS ics to look for broken traces underneath i found out that the problem was software related
i managed to write a dos 360k boot disk and after booting from it, the keyboard worked
strange because i booted the nec hardrive on a 386 mainboard and it booted fine and keyboard worked there
i then deleted some lines off of the config.sys including a mouse driver and ansi.sys and then after rebooting the keyboard seems to work just fine when i boot from the hard disk on the xt mainboard
what a trip
all seems to be fine now, i will be treating the case and inspecting the psu for leaky caps, i will post some pictures tomorrow
glad i did not waste anybodys time
i havent figured out why the dip switches dont affect anything but now that it works fine i think i will not mess anymore with the board

 

[modem7]

i then deleted some lines off of the config.sys including a mouse driver and ansi.sys and then after rebooting the keyboard seems to work just fine

How unusual. I have taken a note in case someone else reports a similar symptom.

i havent figured out why the dip switches dont affect anything ...

I think the first thing to do is to see if software can correctly read the switches in the switch block. There is a process at [here] that uses BASIC. Alternatively, if you have the ability to burn EPROM's, the Supersoft/Landmark Diagnostic ROM at [here] displays the switch settings ([screenshot]).

If the switches are being on/off read correctly, then I guess we have to assume that the BIOS/motherboard combination does not use the switches in the same way as is used in the IBM XT.
Examples:
* For switch 1, the BIOS author may have chosen not to implement a TEST CHAMBER mode like what the IBM XT does.
* Maybe on your motherboard, switches 3 and 4 do not selectively enable/disable RAM banks, and BIOS simply looks to see what RAM it can find.

 

[hbsoftware]

Hi modem7 thank you for the reply. i also found that symptom very unusual and couldnt find anyone reporting the same problem..... About the AT keyboard it was a btc 5349 so after some research i suspect it is an auto sensing keyboard and that explains why it also "worked"

One thing i also noticed was that the computer was taking a LOT of time to boot because i assume it was looking for a floppy drive (i was testing with just the mainboard, vga card and hdd controller) now that i have everything connected it boots "very" fast.

here are some pictures, (not so great quality) of the way i have things set up right now
i am currently painting the case so i will be posting more pictures at a later date
i will be setting aside the monochrome card and will be using a vga card for easily connecting a modern monitor when needed, i have already found a card that works on an 8 bit slot
i am also using a floppy controller wich also has cmos chip but i have removed the battery and cleaned the corrosion
i also posted a pic of corrosion repair on the motherboard wich i cleaned, fixed 2 traces, neutralized the alkaline and then applied nail polish to cover the bare copper.... there are still some remnants green gunk on 2 of the isa slots but thats not coming off no more than that doesnt matter how i try, even 2 hours with 9% white vinegar and then scrubbing..for now i sprayed them with some multi mpurpose lubricant to help stop the corrosion from growing and when i am more confortable with that i will swap those 2 slots. for now i have the cards fitted to other adjacent slots to avoid poor contacts and i am honestly so happy that all works that i dont want to touch anything on a hardware level not to risk introducing problems

i will definetely be trying out those methods to see if the switches are working or not, although i dont have an eeprom burner for now, but i can try the rest of them and report back. i might be buying an eeprom burner in the near future and if i do that i will read the contents of the bios and upload that, maybe you or other users could recommend a "cheap" device for that purpose that can be bought on ebay or other platform that ships worldwide

 

[hbsoftware]

And maybe a bit offtopic but maybe someone finds interesting, here are some pics of my workspace, the reason i dont have a lot of resources and tools for diagnosing pcs is beacuse i "work" mostly with old vacuum tube stuff mostly tvs, but i also have a passion for vintage pcs and especially for vintage mfm / rll harddrives

 

[modem7]

i might be buying an eeprom burner in the near future and if i do that i will read the contents of the bios and upload that, ...

When you do that, you may find that the BIOS is at [here].

... maybe you or other users could recommend a "cheap" device for that purpose that can be bought on ebay or other platform that ships worldwide

The information at [here] may assist you.