Disk drive reconnection and one issue

WIRED UP THE AC POWER CABLE TO THE DISK DRIVE

The AC power cable was reinstalled in the disk drive, with the ground wire connected to the AC box lug and the hot and neutral wires connected to their spot on terminal block TB4 inside the box. The cable runs back to an SMS power card that is plugged into the SMS power connectors that are used for the 1053 console printer, disk drive, 1134 paper tape reader, 1055 paper tape punch and 1627 plotter devices. 

HOOKED UP THE RUN SWITCH AND DISK UNLOCKED LAMP WIRING

When I tested the wires to determine which switch terminals each connected, I discovered that the switch was not working properly. It is a DPDT switch although only the Normally Open and Pole terminals are used. One of the two poles was not connecting to either the NO or the Normally Closed contacts.

I used Deoxit to spray inside the switch and exercise it until I restored a good low resistance connection when it is put in the ON position. The four wires from the switch were inserted into the terminal blocks on the front of the disk drive. A doubled set of wires from the Disk Unlock lamp on the main console was plugged into its spot on a terminal block. 

An end of a wire snapped off the pin connector that was plugged into a terminal block - but I soldered it back together easily. 

SMS POWER CARD SNAPPED OFF - SIGNS OF PRIOR DAMAGE AND BAD REPAIRS

I found that the card was snapped off at the fingers. One of the two finger sections showed signs of a prior break and a repair using some kind of liquid metal squeeze on material. It was also wrapped in black vinyl electrical tape, probably to keep the parts together.

This is the means of delivering 115VAC hot and neutral to the disk drive, as well as a good ground connection to the 1130 frame from the disk drive. I could directly wire this up, but that would not match the way that IBM connected the disk drive. 

DESIGNING NEW SMS POWER CARD TO BE FABRICATED

I fired up KiCad and began to design a compatible SMS power card. Once it is fabricated by JLCPCB I can use one to repair the disk drive connection and keep a few for other possible uses. I think the SSM museum could use one so I will send one to them. 

Assessing a location for the Virtual 2315 Cartridge Facility interface board

MOST COMPONENTS SOLDERED ON INTERFACE BOARD

I had a few hours in the workshop in between time spent with family visitors. I soldered on the connectors, installed the pins that allow me to hook up the cable connector from the 1130 controller logic, soldered on a cable that plugs into the disk drive, and a few other components. I still need to install the voltage regulator, resistors and capacitors. 

TESTED CABLE ROUTING AND MOUNTING POINT FOR BOARD

I had to find a potential location for the interface board where the cables from the disk drive, 1130 controller logic and emulator box can be routed simply and neatly. I did find a good spot, as you can see from the temporary mount with cable ties. 

I will drill and tap for the mounting screws along the left side of the interface board then work out a mount point for the right side. 

Parts arrived to build Virtual 2315 Cartridge Facility interface board

PCB ARRIVED ALONG WITH THE PARTS

This board is the interface between the IBM 1130 disk controller logic, the 2310 disk drive and the modified RK-05 Emulator that together form the Virtual 2315 Cartridge Facility. The cable from the CPU that normally would plug into the disk drive will plug into this new board. A cable attached to this new board will plug into the disk drive. A pair of ribbon cables connect this board to the RK-05, passing most of the signals between 1130 and disk while processing all the data related signals inside the emulator.

FINISHING UP THE FPGA AND C CODE TO BEGIN TESTING

In order to start testing with the 1130 and disk drive, my modifications to George Wiley's RK-05 Emulator must be installed. The 2310 disk drive differs from the DEC disk drives in quite a few ways. As well, my notion of a hybrid of real disk drive plus emulator is unique. 

I will do some final simulations of the FPGA logic before installing it on the FPGA chip in the emulator. The emulator FPGA works hand in hand with a Raspberry Pi Pico that manages the SD Card where the cartridge images are stored, thus there are some Pi side C code changes needed.

Still testing substitute 5806223 card to support 1627 plotter on the IBM 1130

AFTER ERROR OF MISSING PULLUP, STILL HAVE ERRONEOUS BEHAVIOR

The card was producing the 1.9 ms and 50 ms output pulses now. More importantly, the interrupt level 3 request (IL3) was not incorrectly high before commands were issued. I saw the busy status emitted when the XIO Sense Device was issued.

What was wrong was the behavior of both busy and IL3. I saw the flipflop turn on, emitting IL3, when I requested a Drum Up move. However, the line dropped after 100 ms when it should have been latched on until an XIO Sense Device with bit 15 was issued. 

This is incorrect on three levels. First, the flipflop should not turn off by itself. Second, the timing suggests that even though I was issuing one of the 1.9 ms actions, the other pair of timers produced two 50 ms actions; the Drum and Carriage movement commands should create two 1.9 ms intervals. Third, the intervals, whether 50 or 1.9, have no path that should reset the IL3 flipflop.

There might be a short between wires, since this was a very bodged prototype, or a bad gate, but in any case the behavior is incorrect. I will check this further when I get back from a family trip early next week. 

More testing of 5806223 replacement card and redesign to eliminate donor card requirement

CONVERTING THIS TO A DIRECT SLT CARD CONNECTOR ON THE PCB

I found some spring contact parts that would allow me to make a compatible end on my PCB that would slide into the card compartment and mate with the pins in the socket there. This did require some very careful measurement of IBM SLT cards to understand all the dimensions 

I implemented the pads onto which I will solder the contacts. The result will look very much like the original IBM end of an SLT card. I then need a 3D printed cover similar to IBM's black molded plastic part that protects the contacts and guides the card into the slot when it is inserted. 

The spacing of SLT pins in the card slot is .125" or 3.175mm. The connectors will fit easily in that spacing and are about the same width, length and height as the ones IBM uses. 

The plastic cover on the end of a card has grooves to slide over guides in the SLT board (backplane) at each card slot. It has notches to ensure the card can't be inserted rotated 180 degrees. It has .1"x.1" square openings that the SLT board pins slide into. 

I will need to design these covers and print them. I have time since the parts and PCBs will take a week or so to arrive. 

TESTING TO UNDERSTAND WHY INTERRUPT LEVEL 3 WAS ON INITIALLY

I did find that often the 1130 would power up with a level 3 request active. My design should initialize correctly and only drive the request after a plotter command has been executed. I took the card out and put it on the bench, reproducing the erratic IL3 behavior. 

The big breakthrough was while I was redesigning the card to feature an SLT connector. I spotted an error in part of the reset logic for the flipflop that drives the IL3 request. 

A gate will reset the flipflop either when the 1130 system reset signal is active or when an XIO Sense Device with bit 15 set is issued to area 5 (the plotter address). The signal for the latter case passes through an inverter. I realized that the inverter was a 74LS05, an open collector inverter, thus it should have had a pullup resistor on its output but it did not. 

I did a bodge change to the board on the bench and verified the correct functionality. I placed the card back into the 1130 and indeed the IL3 does not come on spuriously. I don't want to spend too much time working on the old design, when I will soon have the integrated SLT connector on the updated board. 

Disk drive bolted back inside IBM 1130 - without additional people

SPENT TIME MEASURING, VISUALIZING MOVEMENTS AND PLANNING STRATEGIES

The disk drive won't slide in from the front nor the back as the vertical height of the drive is larger than the vertical gap to the upper frame rails. Sliding from the side would require removal of CE transformer and usage meter boxes to open up the gap.

After I unbolted the transformer and meter boxes, I lowered them out of the path of the disk drive. I still had an issue because the height from the lowest to the highest part of the drive is too large, even tilting the drive as I slide it in to get over the frame stands that it has to bolt onto. To deal with this, I took the upper sheet metal off the drive to lower the height.

Transformer and meter box relocated

When I attempted to slide the drive in from the side, I found that a plastic bar that anchors the cartridge receiver tilt mechanism was about 3/4" too high to clear the left frame rail even with tilting. 

I had to admit to myself that the only way the drive would get inside the frame is to be lowered from above, exactly the situation that should force me to have a second person or some kind of a crane/lift. 

Inspiration struck. I have a board that is of appropriate size that I could use to sit the disk drive on top of the 1130 frame. If I slid the board backwards then it would pivot down and the drive would start to slide to the front but inside the 1130. Holding the front of the drive near its mounting spot, I could pull the rest of the board out and lower the rear of the drive to its mounting spots. 

BOARD METHOD IMPLEMENTED, DRIVE BOLTED DOWN

The method worked almost as well as I envisioned it. A bit more cumbersome to hold the drive from sliding too far forward while also pulling out a board and lowering the rear, but it did do the job. 

The bottom of the drive has four threaded studs that fit into holes on frame supports. I added the bolts and nuts to secure it down. To wrap up, I put the sheet metal parts back onto the drive. 

threaded stud with rubber donut on left side of picture

NEXT STEPS

When I get back into the shop, I will replace the CE transformer and usage meters to their proper positions and put the tops of the machine back on. 

• I have to connect the AC power, the Run switch and the Unlock lamp to the front of the drive. 
• The rear has a set of DC power connections to reattach for +3, -4, +6 and +48V. 
• A duct for cooling air entering the rear of the drive will be reattached to a frame member
• The run switch bracket must be attached
• The faceplate will be remounted in front of the drive opening
• Normally the signal cable from the CPU would be plugged into the drive's card cage

Since this will run with the Virtual 2315 Cartridge Facility emulator sitting between the 1130 and the disk drive, the connector going into the drive will come from the facility. I am still waiting for the PCB fab house and parts suppliers for what I need to make that drive connection. 

Another possibility for eliminating need for donor SLT cards when making substitute cards

SMT SPRING CONTACTS MIGHT ALLOW ME TO MAKE PCBS WITH INTEGRAL SOCKETS

I found some gold plated spring contacts that are .098" wide and solder onto a PCB pad. They can be set side by side to form the 12 connections on each side of an SLT connector. Their height above the PCB will create a .257" width between the two sides of the card. Since the SLT backplane (board) pins are spaced at .25", this should give a decent fit with adequate quality connection. 

I ordered some and will experiment to see how they work with real SLT boards. This is easier than having wires running from PCB pads to a standalone connector which must be anchored somehow to the PCB (see earlier post).