Mystery IC: Allen Bradley 314B102

Paul Berger phb.hfx at
Thu Dec 17 07:08:02 CST 2015

On 2015-12-17 2:26 AM, Mike Ross wrote:
> On Wed, Dec 16, 2015 at 8:01 PM, Brent Hilpert <hilpert at> wrote:
>> On 2015-Dec-15, at 6:21 PM, Mike Ross wrote:
>>> On Wed, Dec 16, 2015 at 11:43 AM, Mike Stein <mhs.stein at> wrote:
>>> I have taken Brent up on that :-)
>>> I'll poke a bit more myself and see what we can work out together
>>> before I decide if the effort is worth it.
>> First crack can be picked up here:
>> There are a few areas and pins I couldn't discern from the photos.
>> Mostly around U1 & U6 as the lens angle and lighting is hiding some connections around those.
>> If you take another photo or check some of the connections marked in red I can update the schematic.
>> I've labeled the host interface connections as per the most likely scenario:
>>          D0-D6: in correspondence to the 'normal' PROM addressing, so D0 is likely the ASCII LSB.
>>          nSTB: this should be the print-strobe input, looks like active-low.
>>          BUSY/RDY: haven't examined the logic enough to say whether this active-high or -low for whichever way one chooses to interpret it - BUSY / READY / ACK.
> Amazing work Brent!
> I've wired the thing up in accordance with your schematics and here
> are the results:
> On power-up the line we believe is Strobe is high; all others are low
> - and I'm monitoring the printer side of the interface here.
> I cat > /dev/lp0
> The printer prints a character; Linux is waiting. The line we presume
> to be Busy/Ready flickers briefly high as it is printed.
> I toggle the local/com switch from com to local and back to com:
> another character is printed. Linux waits. I can sometimes continue
> this process one character at a time by toggling the local/com switch.
> At other times toggling the switch sends Linux straight back to the
> command prompt.
> The characters printed are pretty exclusively semicolons underscores and 8s.
> The carriage never advances; all characters are printed at the same spot.
> Further observations:
> - If I initiate the print with the Strobe line disconnected Linux
> returns to the command prompt instantly and nothing is printed.
> - If I disconnect the Strobe line after printing has started Linux
> returns to the command prompt instantly after the com/local switch is
> cycled
> - If I disconnect the Busy line prior to starting to print nothing is
> printed until I connect the Busy line
> - If I print a character by cycling the local/com switch with the Busy
> line disconnected a *second* character is printed when I reconnect it.
> - Busy flickers high every time a character is printed. The status of
> the Strobe line never visibly changes; it always appears high. Might
> put a scope on those...
> There's clearly something funky going on with signaling - timing or
> active high vs. active low. At no time does the printer *ever* print
> more than one character without some manual intervention.
> 'No greater love hath a man than he lay down his life for his brother.
> Not for millions, not for glory, not for fame.
> For one person, in the dark, where no one will ever know or see.'
1. If the carriage never advances that is a mechanical problem, the 
escapement is triggered by a cam on the filter shaft.  If the cords are 
off, these are white nylon cords attached to each side of the carrier, 
the carrier will not move.  It is also possible something is jamming the 

2. There must be more electronics in this than the one card.  There 
would need to be a 5V  power supply for the logic and 48V power supply 
for the solenoids (magnets).  There would also need to be drivers for 
the magnets, there is nothing on the board with the logic to drive the 
48V magnets.

3. It would be helpful to know where the signals inside the typer go.  
My guess would be the outputs from the PROMs would go to drivers for the 
selection and function magnets, and one of the others must go to pick 
the cycle clutch, but there would need to be some way to inhibit that 
for functions, and I don't see that on the schematic.  Some of the 
inputs on the extreme left of the diagram likely go to feedback 
contacts, but it would be helpful to know which ones.

4. It is possible the expected feedback from the typer is not happening 
due to a contaminated contact.  If the contacts are gold coloured, they 
are gold plated and you should not use anything abrasive to clean them.


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