Working on the 3174 EIA wrap test plug until the diagnostic runs clean, controller tests out good

 WIRING UP THE WRAP TEST PLUG

I used the diagrams from the 3174 maintenance manual to build an EIA Wrap Test Plug. I had noted that the diagram is ambiguous as to whether the wire between pins 14 and 16, representing an encoded plug type, should also be wired to signal ground (pin 7). I left that off in my first attempt since the wording of note 4 of the diagram is "Pins 14 and 16 are wired together in the wrap plug." but doesn't mention the connection 7 to 14 that existed in the regular cable. 

Wired as EIA wrap test plug

FIRST TEST FAILED IN ERROR - VALID CONNECTOR NOT PRESENT

I ran the diagnostic to check out the communications adapter interface using the wrap test. This is selecting by choosing the hardware group 11 (type 1 comm adapter), then selecting test 02 (interface wrap test).  

Results of wrap test

The cryptic codes are read using the IBM 3174 Status Codes manual. The code 3030 tells us that a communications adapter test failed, running test 02 on hardware group 11. Specifically it says that there is not a valid communications cable or wrap test plug connected. The final two parts point to the field replaceable unit that contains the failing circuitry - the motherboard in this case because the communications adapter is integrated onto the planar board. 

ADJUSTING PLUG WIRING AND SECOND TEST

I added the wire from signal ground (pin 7) to the two ID pins (14 and 16), as the alternative interpretation of the incomplete description from my wiring diagrams. I then re-ran the test to see if this time it finds the wrap test plug and completes the test successfully.

Cable identification issue

I received a quite different error, after the diagnostic ran a number of tests on various signal lines - toggling the outbound pins while observing the inbound pins where they were wrapped. The error message states "EIA 232D/CCITT V.35 wrap plug failure or X.21 interface cable installed on an EIA 232D/ CCITT V.35 adapter card or a Concurrent Communication Adapter (CCA) is installed in an invalid location." and that points to a wiring issue with my wrap plug. 

I don't have a CCA so the issue is either that the wrap plug is missing a loopback signal or the processor believes that this is an X.21 interface cable. I can see that the X.21 cable has both pins 14 and 16 tied to signal ground pin 7, which is how I changed my wrap plug wiring. I am therefore working on the assumption that I am mis-identifying as an X.21 cable. 

ALTERNATIVE USE OF STANDARD EIA CABLE WITH TEST SWITCH ACTIVATED

The cables sold by IBM have a switch on them, labeled Oper/Test, which provides wrap back of signals. The only differences from the wrap plug are the removal of the wire from pin 18 to pin 22 and the removal of the wire from pin 14.

This was an easy modification so I rewired and performed another test. This way I am following exactly the wiring of the EIA cable with the switch set to TEST. The outcome was quite a bit better. This tells me that the wiring to identify the EIA wrap plug was neither of the two choices I tried. 

Successful completion of interface wrap test

I did some other testing, such as port wrap tests on the terminal connections (hardware group 26) which all came back clean. The only error I was receiving now was that floppy drive was not ready (since I didn't have a USB stick inserted.

REGULAR IML WITH THE EIA CABLE/TEST SWITCH PLUG IN PLACE

I decided to switch over to the Control diskette image and attempt a regular Initial Microprogram Load of the device It chugged along, passing the spot where it through up past errors complaining that no communications cable was installed. Eventually it got to the end, displaying 3174 on the operator status panel as evidence that it was fully loaded and operational!

I then requested the online tests by holding down ALT and hitting the TEST keycap. The terminal switched into TEST mode and allowed me to display the main test menu. 

Online test menu displayed

I worked my way through a number of these, such as displaying the event log, erasing the log, testing my terminal and displaying various configuration and vital system information. As an example, it listed the hardware detected on my system, which gave me a pleasant surprise. Although the written markings inside the controller suggested it was the first generation 9021 board with only 512K of RAM, the test system confirmed that I had a later 9025 planar with 1MB of memory configured. 

Hardware configuration displayed

The vital data for the system shows all the versions, patches, maintenance releases and the controller serial number. 

Vital data display

I did extensive testing and everything appears totally operable and ready for my use once I get this connected to my P390 and/or Hercules systems. After a while the controller realized that it wasn't really communicating with a host system and put up error 0532 on the operator status panel with subcode 1011 warning me the BSC line was idle with no polls coming from the mainframe. 

This is absolutely to be expected. As well, the status line on the display showed the communications error 532. 

Communications error 532 - host not polling the controller