IBM 5100 Restoration in progress

Santo Nucifora santo.nucifora at
Wed Mar 18 05:58:10 CDT 2015

Hi Christian,
Thank you for the reply.  I think I mentioned the machine halts or my
keyboard doesn't work or it's not far enough in the Bring Up test to allow
the Diagnostics to come up with the special key sequence.  This is new
territory for me so I'm not sure if input is accepted at that point.

Where did you find the code for the Bring Up tests?  I would love to have a
look.  The 5100 Maintenance manual is not very specific and certainly
doesn't have code in it (unless I missed it).

My registers looks like this:

You'll notice that the first two characters in second line is not right.
Sadly, it's gotten a little worse after taking this picture so lines 5 and
6 have some garbling of the dots. Since I was seeing text, I didn't suspect
the display card right away (again, not knowing the machine) but it may be
bad RAM on the display card.

I'll refer to your  IBMparts.txt file and see what is on that card.  If you
do see anything else in the registers, I'd be very happy to hear your

Thank you!  I now have renewed hope.

On Wed, Mar 18, 2015 at 6:27 AM, Christian Corti <
cc at> wrote:

> On Tue, 17 Mar 2015, Santo Nucifora wrote:
>> Update:  Unfortunately, I think I'm at a dead end.  After cleaning
>> everything up, I am still at the "A" in the "Bring Up" program that isn't
>> very far but it's better than garbage.  I removed both memory cards and
>> get
>> garbage so the memory cards might be working (I have two and tried both
>> individually).  I think my problem is in the "Basic I/O" card as indicated
>> in the Maintenance manual.  I am also not able to get into the Diagnostics
>> screen because it must be failing too early.  Either that or my keyboard
>> isn't working.  It's hard to tell.
> What you don't say is whether the machine just halts, or stops with a
> machine check.
> Here's the relevant part of the Bring Up test 'A' from the 5110. Since I
> still haven't got a 5100 I can't verify what the 5100 does, but I suspect
> that it must be quite similar at this point.
> [...]
>                         ; --- Test A ---
>                         ; Bus In bit test
> 0078    251E            MOVE R5, $3C
> 007A    81C1            LBI R1, #'A'
> 007C    7150            MOVB (R5)+, R1
> 007E    8FFF            LBI R15, #$FF
> 0080    00FE            GETB R15, $0
> 0082    CF04            SS R15
> 0084    0000            HALT
> [...]
> So essentially, the routine reads the byte from I/O device 0 (the
> processor or display adapter card) and halts if it isn't $FF.
> You should be able to check what R15 contains after the halt by switching
> to the register display.
> According to the 5100 MIM, the 'A' routine is described as "Test bus in
> for the ability to turn all bits on". So apparently you have a stuck bit.
> Are you shure that you don't have any external devices attached to the
> machine? And check the top connectors and all the jumpers.
> Then you might find the stuck bus in bit with a scope/logic probe by
> probing the external connector A2.
>  I'd be happy to try to replace some of the logic chips but IBM uses their
>> own numbering scheme.  Does anyone know of a way to read them?  I assume
>> they are normal logic chips but with IBM numbering in most cases?
> The normal "black" TTL ICs, yes, they are standard ICs. For a (incomplete)
> list, have a look at our FTP server at /pub/cm/ibm/ibmparts.txt
>  You can find new pictures here:
> One note: the terminator box is only needed when you use the 5106 drive
> *without* the 5103 printer, because the printer has a terminator built in
> and thus must be the last device in the chain.
> Christian

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