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xave
March 13th, 2014, 10:41 AM
Hello everybody,

First of all, pardon my English, I am French (and not the opposite ;) )

I recently bought an IBM PC/XT with 256Kb of RAM on board and an extension board of 256Kb and a 10Mb hard-drive.
The first time I switch it on, it didn't boot. I rapidly realised that a capacitor on the hard-drive control-board was short-circuiting the PSU, so I change it.
After the fix, everything was working perfectly, the computer was able to boot. the POST was showing 512Kb and It was booting on DOS 2.0.
So I decided to buy the XT IDE from Lo-tech. But, when I plugged it on, only 64Kb was recognised in the POST and, without any error. Now even without the XT-IDE card only 64Kb is recognised.
I try to remove/put back all the chip on socket, but noting change...

Help! Help! What did I do wrong!

z80eu
March 15th, 2014, 06:15 AM
Hello everybody,

First of all, pardon my English, I am French (and not the opposite ;) )

I recently bought an IBM PC/XT with 256Kb of RAM on board and an extension board of 256Kb and a 10Mb hard-drive.
The first time I switch it on, it didn't boot. I rapidly realised that a capacitor on the hard-drive control-board was short-circuiting the PSU, so I change it.
After the fix, everything was working perfectly, the computer was able to boot. the POST was showing 512Kb and It was booting on DOS 2.0.
So I decided to buy the XT IDE from Lo-tech. But, when I plugged it on, only 64Kb was recognised in the POST and, without any error. Now even without the XT-IDE card only 64Kb is recognised.
I try to remove/put back all the chip on socket, but noting change...

Help! Help! What did I do wrong!

May be you didn't do anything wrong.
If you already checked all chips in sockets on board, first thing to do is to narrow down the problem.
Hopefully you did all changes without connected power etc. (yes, I know this is trivial but some are too hasty when trying things to change).
So try to remove all cards you don't really need (e.g. also the 256KB RAM extension board).

Do you have a Diagnostic Card like this one http://www.ebay.com/itm//360879135243 ?
Or do you have a second motherboard / computer to test/exchange the RAM chips ?
What do you mean with "only 64KB is recognized" - BIOS power on test ?

modem7
March 15th, 2014, 01:56 PM
Do you have a Diagnostic Card like this one http://www.ebay.com/itm//360879135243 ?
Unfortunately, the IBM 5160 (XT) does not output codes that can be read by such a card. See [here (http://www.minuszerodegrees.net/misc/post_cards.htm)].

modem7
March 15th, 2014, 02:02 PM
Welcome to these forums.


After the fix, everything was working perfectly, the computer was able to boot. the POST was showing 512Kb and It was booting on DOS 2.0.
So I decided to buy the XT IDE from Lo-tech. But, when I plugged it on, only 64Kb was recognised in the POST and, without any error. Now even without the XT-IDE card only 64Kb is recognised.
I try to remove/put back all the chip on socket, but noting change...
The symptom that you describe results from a design flaw in the IBM 5160 (and 5155). You can read about it [here (http://www.minuszerodegrees.net/5160/problems/5160_known_problems_issues.htm)].

So, in your 256K type motherboard, either a chip in bank 1 [diagram (http://www.minuszerodegrees.net/5150_5160/ram/5150_5160_ram_banks.jpg)] has failed, or a chip in bank 1 has developed poor contact with its socket.
You have reseated the chips, and so the cause must be chip failure.

xave
March 16th, 2014, 08:56 AM
I finally found the problem. It was a chip in bank 1 that was faulty. I first remove all the chips from bank 1 and switched them with bank 3. after that the POST was going to 192Kb. Then I used 4 chips from My RAM extension board and narrow the chips to finally find the bad one.
It's weird it happened when I installed the XT IDE card. It really freaks me out!
Now I have to buy a new chip. I found a very cheap shop here (http://www.aliexpress.com/item/Expanding-machine-for-echo-IC-M5K4164ANP-15-M5K4164AP-15/1606119021.html)
Thanks for your help and encouragement.

modem7
March 16th, 2014, 08:45 PM
It's weird it happened when I installed the XT IDE card. It really freaks me out!
I am very sure that is was purely coincidence.

I have added your faulty motherboard to the list at http://www.minuszerodegrees.net/vcf_motherboard_failure_history.htm