I wired diodes across the relay contacts in my box in order to absorb any induced back EMF from the opening of the coils. Electrically it would be more ideal to install these at or close to the punch solenoids in the 029, but we are trying to keep the keypunch modifications to a minimum. However, the small gauge wire connecting to the interface box will have to absorb the current spike flowing through the diodes.
|Diodes added across relay contacts in order to quench back EMF from keypunch coils|
I made up the dummy plug and verified that the keypunch works properly with the interface disconnected. Therefore, there is no damaged component in the keypunch. I hooked up the punch cable to my box, leaving all other cables including power disconnected. The keypunch worked properly one time with cards but after a clear cycle, it was again failing to recognize when the next card was registered.
|Dummy plug for punch cable when box not attached to keypunch|
I tested every wire going into the box from the punch cable and they were all infinite resistance to each other, except for the pair for multipunch pole 2 which are normally closed. I ran the keypunch with the dummy plug for a while, then plugged in the punch cable but otherwise had nothing connected to the interface box. This worked well for about five or six cycles of registering, spacing and clearing cards.
I then plugged in the power brick connector (but no AC was hooked to the brick), which locked up the keypunch on the second cycle. Very odd. At this point I have to suspect that a connection is intermittently shorting somewhere in the SMS block, so that small movements of the cables introduce the error.
CHI SAC INTERFACE, DISK CONTROLLER AND DIABLO DISK DRIVE
I powered up the CHI interface electronics and they came up cleanly. Looking over the cards, I came to the conclusion that it appeared likely to be working properly. As I result, I will cable this to the SAC interface and give it a try later tonight or tomorrow.
|CHI interface looking good, decided to begin testing it|
|Superficially clean drive, but some marking on a cartridge where the heads flew|
SAC INTERFACE FOR ADDING PERIPHERALS TO THE 1130
I picked up the solder this morning and rewired the demo receiver circuit, which is hooked through a transmission line (I twisted wires together from the driver output and from the receiver input, then connected those twisted pairs temporarily). This is intended to verify that TTL input signals to the driver will be properly reflected as TTL outputs from the receiver, as well as my verification that the voltages are at appropriate levels in both states.
The circuit worked perfectly. I varied resistances to ground on the TTL input to the driver to see at what voltage it would switch between on and off. It will recognize a logic level 1 down to .1V but is off somewhere above .066V, well within the specifications for the logic I will use to drive signals towards the 1131.
|Driver circuit on top and receiver circuit at bottom - working perfectly|
I lieu of testing this, I powered up the CHI interface and disk drive (see above). I may do some XIO tests to determine how the CHI interface is responding (and to what addresses), but the important testing will be with my circuits once I move on to try them with the SAC.
I went ahead and ordered the transistors, diodes and resistors I need to implement the full interface which will give me TTL logic on my side and for the other side it will deal with the 1131 SLT transmission lines coming out of the SAC interface. I expect to have all the parts by the end of tomorrow, thus doing the assembly on Thursday and Friday.