Huge IBM 1800 find (and need some help)

Jon Elson elson at
Sat Mar 21 14:39:33 CDT 2015

On 03/21/2015 01:47 PM, Johannes Thelen wrote:
> Thanks Jon for tips!
> No, that is not option, I mean 2311 is have to get back to life ;)  I think use ultrasonic or carbon ice cleaning for 2311 and disk packs. Both are quire gentle cleaning methods.
You have to be very careful with anything that requires 
temperature extremes.  Can anybody verify the 2311 uses the 
hydraulic head positioner?  If the oxide coating of the 
packs has deteriorated, which I think is quite possible, 
then the disks will not be usable. Anybody else have 
experience with 14" disk packs from 40" years ago?

The other problem is this machine uses SLT.  That was never 
a super-reliable technology.  They start with 1/2" square 
ceramic substrates, and fire thin film resistors onto them, 
then print and fire thick film wiring.  Then they use 
bump-bonded discrete transistors and diodes, and solder 
these by bump bonds to the wiring, and add leads.  Then, 
because the transistors and diodes are not well-passivated, 
they smear silicone goop over it and epoxy on the die-drawn 
aluminum covers.  These are not totally hermetic, and oxygen 
gets inside and slowly deteriorates the semiconductor 
devices.  They also had some problems with the solder joints 
to them developing cracks.

So, the likelihood of the CPU actually working after FORTY 
years of storage is pretty small.  There are, of course, no 
replacements for SLT modules, as IBM stopped making them in 
the late 1960's!  It was a form of diode-transistor logic, 
and not terribly dense.  A single flip-flop would not fit in 
one SLT module, it took at least 2, and the usual scheme was 
to integrate some steering gates with it and ended up with 
about 4 modules to implement the typical register bit.  They 
didn't use what we think of today as a FF, they used D 
latches, as it was simpler to implement, but required 
several clock phases.  One clock phase to latch input data 
to the ALU, wait for the ALU to settle, then a pulse to 
latch the result out of the ALU.
>   I like to dump core and all disc packs for future uses ( = make original configuration).
I wouldn't worry about what is left in core, it would be 
interesting, but you might have to do a lot of testing and 
repair before enough of the machine is working to read it out.

Be very careful with the disk drives.  If you even get a 
scratch on the heads, you will not be able to replace them.  
Also, if anything at all happens to the heads, you will need 
an alignment pack to realign any replaced heads.  Do you 
have ANY experience with old-school mainframe equipment?  If 
you think you will just dust this thing off, mount the disk 
packs and fire it up, you are quite crazy!


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