Resumed testing of M1000 card reader, reassembly of P390's x235 server

 QUICK ADJUSTMENT OF MAGNETIC PICKUP POSITION USING CARD

Since a punched card is approximately .007", the specified distance from the pole of the magnetic pickup to the highest point of the teeth on the timing wheel, I used a card to set the pickup position. With that done, I powered up the reader and testbed to verify that the pulses are arriving properly. I made use of my card extender to easily get to the comparator output on the clock card that emits the timing pulses.

Pulses produced by magnetic pickup through comparator

The pulses look great. Nice and regular, cleanly shaped, definitely good for driving the card reader sync logic. That shows it is time to fire up the logic analyzer and record a card going through the machine. 

LOGIC ANALYZER TRACE OF THE BACKPLANE SIGNALS DURING A READ

The analyzer was set to trigger on the appearance of OneDark, representing the moment that the card edge first occludes any of the LEDs shining into phototransistors for the 12 card rows. I triggered a card and saw that we had a good capture. Further, the machine went into Stop mode and shut down the vacuum/blower motor, which it should do when an error condition arises. In this case the error condition is Hopper Empty Check, which is in fact the expected result since there was only one card in the hopper. 

I went through the trace and found most signals appearing exactly as I would expect. The only one that wasn't in my trace was STOB, but there could be one of three causes. It may not appear in the interval from OneDark through the end of the analyzer buffer, it might be an actual defect in generation of the signal, or it might be yet another bad wire between the backplane and the analyzer. 

I did see the logic signals that cause IM to be emitted on the external interface, but didn't put a scope on the actual IM wire to verify it is present. The buffer is too shallow to hold the full set of clock cycles from OneDark to the completion of reading a card. The duration of a read at full speed is about 60 milliseconds, so perhaps 45 ms is the required capture. With the clock operating at 480KHz, that would require a buffer depth of more than 20K or almost 8 times the capacity of my analyzer. 

The solution to checking the signals at the 80th column through the end of the pick cycle is to trigger on the signal 80CR, so that doesn't really pose an issue. When I next go to the workshop I will watch IM on the external interface as well as doing a column 80 capture. Another capture I will set up for is watching some of the row data signals on the interface to see that they make sense. 

CONTINUING ASSEMBLY OF THE x235 SERVER FOR THE P390

I was able to force the rod through the blue plastic holders to get the PCI card area in shape. It took quite a bit of persuading but I was triumphant.

Plastic card holders in position and ready to hold cards

I then began reattaching and reinstalling various parts of the machine. I have to be careful to ensure that all the proper cables are in their respective connectors and not misplaced, but the mechanical parts are pretty obvious

Slowly putting the server back together