Reassembly of the 1132 printer - part 9

REED RELAY REPLACEMENT PCB ASSEMBLED AND ATTACHED

A complex reed relay (RR1) was discovered to have an open coil. This relay has four reed switches - two are normally closed and two are normally open. Three of the four switches are used by the PCB that contained this relay. It had a 48V coil. 

The RR1 relay activates when the printer controller logic in the 1130 has activated the Carriage Magnet to move the paper down one line or to skip until a hole is detected in some channel of the carriage control tape. 

Three relays RR1, RR2 and RR3 are used in order to have the Silicon Controlled Rectifiers energized from the time the Carriage Magnet is activated until the printer carriage reaches the next line position where the Carriage CB switch closes.  

I was not able to find a similar reed relay but worked out a solution using a pair of SPDT reed relays to substitute for the three reed switches that were used in RR1. The relays were not 48V, thus I also had to drop the voltage to the 5-6V range of the parts I bought. A small PCB I designed mounted the two reed relays and the dropping resistor. 

I installed the two replacement reed relays, which were in 8 DIP form, plus a 2W resistor onto my new PCB. I added wires between this small PCB and the main IBM PCB which had contained the failed RR1 relay. 

CARRIAGE CONTROL TAPE PCB REINSTALLED

The IBM PCB mounts on the side of the frame at the right rear of the machine, with three connectors that plug into it from two sides. With that in place, I mounted the small new PCB with my relay substitute just above it. 

FORMS TRACTOR AND PAPER FEED GUIDES INSTALLED

The printer uses continuous forms with pin feed holes on the two edges of the paper. A tractor mechanism holds the paper with pins through the feed holes and advances it when the platen turns. This was inserted on top of the carriage mechanism.

A guide attaches to the top rear of the carriage to guide the new paper up into the forms tractor and to guide the printed pages as they come out of the machine. Often the operator would have a box of blank forms up against the rear of the printer with the paper fed up through the tractor and then an empty box behind the blank paper box to catch the output as it comes down from the paper guide.