The SPERRY UNIVAC UTS 40 system + 8406 double-sided diskette subsystem : Restoration

Dominique Carlier dce at
Mon Oct 2 11:13:04 CDT 2017

Hi everybody,

Here is the next episode of the restoration of my UTS 40.

During the previous “season”, I was talking about buying a wreck of an 
UTS 40 from the USA.

  I had taken the risk to buy it, after the conclusion of the sale, the 
seller had retracted, I had argued with him, I finally put a bad note on 
Ebay. However, surprise! The guy still sends me the machine. This one 
remains blocked during a full month at the Belgian custom house. I 
finally receive it, and now, if you like horror movies, you will be happy.

Here is the state in which I received the machine:

I never - never! - received a package in this condition !! The reason 
maybe was the hideous and ridiculously “protective” packaging ? Possible 
... or in the plane they 400kg over my UTS ? Possible ... but we still 
have the impression that someone hammered the machine, even the very 
solid plastic pieces have also shattered.

As I am an optimistic guy, I think "the plastic ... not important, 
fortunately the chassis and the electronics of this machine is build 
like a tank".

I analyze the boards, as expected, some architectural differences but 
not so much. Here is the CPU board:

Unsurprisingly, the battery has sunk and there are damages:

With courage I clean the board, I replace some resistors, one capacitor, ...

and I replace the battery (2,4V ? A doubt persist)

And comes the time of the first test and it boot!

The POC test at startup is not successfull but from the outset, this 
allows me to analyze and diagnose some elements of my own UTS 40, here 
is what I notice:

- The program cartridge of my UTS 40 is functional
- The power supply to my UTS 40 is OK
- The video circuit of my UTS is OK
- The keyboard of my UTS requires a restoration (aluminum discs, foam 
cylinder, classic issue of old keytronic keyboard)

- The absence of the backup battery is not a problem, the machine can 
boot, without this it can successfully passing the POC test and the 
encoding of the parameters in the setup page is possible.

I discover other interesting things about the relationship between the 
cartridge program and the hardware configuration.

- These program cartridge are made for a specific hardware 
configuration, for example the RAM repartitions at the level of hardware 
has an impact on the result of the startup test. The number of kilobytes 
checked, the memory extension considered as PASSED or FAILED. Even the 
installed memory is working and assignable, with a configuration that 
differs from the hardware intended to run with a specific Program 
Cartridge, the POC test could show that a memory is missing, simply 
because the RAM is not physically in the slot or socket according to the 
program specification in the cartridge.
I drew this conclusion because the CPU board form USA has 64Kb installed 
on it, and 27 empty sockets, I filled them with RAM and now with the 
program cartridge form Ebay, 4X  64KB are detected and flagged with a 
However with my program cartridge, it detects a second memory extension 
as PASSED, but considers the first extension FAILED, I think that on the 
original CPU board, there was only 32kb, even 16kb and non-extensible on 
that board (hence the presence of two memory expansion boards in my 
original configuration). Briefly, according to the inserted program 
cartridge, the tests are sometimes but not always dynamically adaptable 
to a given configuration.

- A cartridge program can be programmed to operate only with a specific 
model of PERIPHERAL I/O board. The program cartridge form Ebay does not 
work with my PERIPHERAL I/O board, however my program cartridge seems to 
detect the PERIPHERAL I/O board of the US.

- I recreated the breakdown of my machine with the hardware of the other 
UTS. I'm talking about the situation of a long BEEP + blank screen, this 
happens if I remove the unique memory expansion board in the original 
configuration of the UTS from Ebay, this could mean that my own CPU 
board is maybe OK and that this could be one of two memory extensions of 
my machine that has a problem (Hypothesis).

But now, without documentations, without diagrams and schematics, 
without info, I'm blocked on a problem, at the beginning it was 
intermittent, now it's constant, and even aggravated, the explanation:

Here is the best result I could get with the following configuration: 
CPU board form US + my PERIPHERAL I / O board + memory extension from US

The POC test is successful, it loads the default settings in non 
volatile RAM:

And I can access the setup page:

Everything would be perfectly fine if most of the time I did not have at 
startup an error at line 9. of the POC test:


This error blocks the machine, it does not load the default settings, I 
no longer have access to the setup page.

I continued to clean the board, looked for damage related to corrosion 
of the CPU board because of the battery, but today it is not better, it 
stops at line 8 of the POC TEST:

However, it could be inferred that this is because the machine can no 
longer determine whether the status of the SERIAL I / O CHANNEL B is 

Last thing, the few times I was able to go into the setup page, I rushed 
to try to encode (with the dead keyboard) the information to declare the 
subsystem and finally return to the CP/M mode. And I had twice the fig 
case where busy to enter the data, without warning hop! Blank screen, 

We have here some interesting information about the intermittent nature 
of the failure, could this give information about the type of component 
in default?

So I have not yet been able to return to the CP/M mode.

My questions are:

- What exactly is "SERIAL I/O CHANNEL B" in this machine?
- What components are used by this SERIAL I/O CHANNEL B?
- Is there really no way to find the schematics of that CPU board? Or 
better, the complete machine, including the PSU?

I think that if I can fix that problem, I could go back to the setup 
page and restart the machine in CP/M mode, in fact it is the last 
obstacle, if I solve this problem my machine is fixed.

Thanks in advance for your help !


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