More this and that, while waiting

BUILDING BRACKETS AND COATING THE 1130 MRAM BOARD FOR INSTALLATION

The gates in a Solid Logic Technology (SLT) generation mainframe have multiple compartments, each hosting as many as 96 SLT printed circuit cards which plug into a printed circuit board that interconnects those 96 card slots plus some top and bottom signal cables. One side of the compartment has the large board with about 2,500 wire-wrap pins that form the 104 sockets for SLT cards or cable connectors. 

The other side of the compartment is a metal cover behind which the SLT cards are inserted. These cards are oriented so that air flows in the 'aisles' between the cards, from bottom to top, to remove heat. Fans sit on the bottom of the compartment and pull air through filters to blow it up over the SLT cards. The top of the compartment is a grill through which the warmed air exits.

Compartment C1 in gate B housed the original core memory for this IBM 1130. It has a three dimensional core memory stack installed on the big board in place of about half the card slots. The remaining card slots have SLT cards which provide the addressing, driving and sensing circuitry for the core memory. 

Since the core memory stack has irreversible corrosion that is eating internal traces, it is no longer feasible to use it on the 1130. I developed a printed circuit board to replace all of the functionality of that card compartment. The three cables which connect this compartment to the rest of the 1130 circuitry are plugged into my PCB instead of the big board in the compartment. All power connections to that compartment are removed, thus nothing is operating in the compartment; my PCB serves as the core storage for the system. 

My PCB is mounted inside the compartment, just below the top grill where the hot air would escape. The three cables originally plugged into the compartment backplane in the top connector slots T1, T3 and T4. My board has those cables fitted and is suspended at an angle inside the gate just below the grill so that it is cooled by the airflow from the fans below. 

SLT backplane/compartment

mounting method

I cut some brass to form the brackets that will hold the PCB at a diagonal under the grill, permitting the existing SLT cards that are inactive to remain in place. The PCB and its brackets were given conformal coating to keep the electrical components insulated from any contact with the compartment walls or grill. The coating should be fully dry by Wednesday when I intend to bolt the memory PCB in place and close up the 1130 system. 

STILL FIGHTING WITH THE HEAD CLAMPS OF THE DIABLO 31 DRIVE

The Diablo model 31 disk drive mounts two read/write heads on the arm, one each for the upper and lower side of the disk platter that is inside the 2315 disk cartridge. These are held in place by three clamps - one each for the upper and lower head holders and a third that holds both head holders in place.

These had been loosened too much and could not be tightened into their proper position. The upper and lower head holder clamps have a tang at the bottom that nestles into a groove on the drive, keeping the clamp upright so that the bolt simply loosens or tightens it. The bolts had been turned too many times and now the tang was not in place, allowing the clamp to spin around. 

Access to the area where the clamps sit is exceedingly restricted and hard to even see into. I finally pulled out a fiber optic camera on a cable that I could push into the area and try to get enough visibility to work. Below is a view from the camera of one of the two head holder clamps, rotated out of position but at least with the bolt still threaded into the end. 

View through the fiber optic camera - not great

I was able to finally work the lower head holder clamp into position so that it tightened up, held from rotation by the tang. That took quite a bit of fussing and work until I finally got the clamp in place.

I then began working on the upper head holder clamp, but that seems jammed against the lower clamp or perhaps against the third (common) clamp. I need to get this one sorted out before I can move on to the third clamp which should be easier to orient once I slide one of the head holders into place. I ran out of steam; this will be waiting for me when I get back into the shop.

CREATING THE BUILD AND INSTALLATION MANUAL FOR THE V2315CF PROJECT

I am now at a point where I will be finalizing the debugging of the Virtual 2315 Cartridge Facility (V2315CF), an ambitious feature that works with the internal disk drive of the IBM 1130 to allow access to a wide range of cartridge images either archived from real disk cartridges or created on IBM simulators. These can be mounted and accessed as if they were real physical disk cartridges, with the internal drive spinning and the arms moving in and out. 

However, the heads do not actually load down onto the one physical cartridge that is inside the drive, thus eliminating the risk of crashes that could destroy the rare disk heads or the disk cartridges. The data for a virtual 2315 cartridge is held on a microSD card inside a little 2" replica of a cartridge which is plugged into the V2315CF main box. The data that is ready by the 1130 comes from the virtual disk image, rather than the heads in the drive. Any data written or changed by the 1130 will be stored on the virtual cartridge's microSD card. 

Virtual cartridge images can be transferred to and from the IBM 1130 simulators that run on modern computers. As well, the collection of physical 2315 cartridges that I have collected will be archived by the other current project, the Diablo Archiver, so that they can be used on the V2315CF. 

The only issue that was outstanding when I had to walk away from the debugging (due to the core memory of the 1130 failing) was the coordination of seeks (disk arm movement between the 203 cylinders of a 2315 cartridge) between the internal disk drive, IBM 1130 and the V2315CF. I am optimistic that this will shortly be resolved, after which I can finalize the installation of the V2315CF in the IBM 1130 that belongs to the Vintage Computer Federation and which I am restoring. 

This is a complicated system that involves modifications to the internal disk drive, several printed circuit boards, a complex power system with battery backup, and the main box of the V2315CF. The main box is an extensively modified derivative of George Wiley's RK-05 Emulator which he built to emulate the DEC disk drive which is a derivative of the internal disk drive from the IBM 1130. There are also the virtual cartridges, software to transfer the disk images and changes to the RK-05 Emulator kit. Finally, a plexiglass case mounts the main box and some of the other components inside the top cover of the IBM 1130, right atop the internal disk drive. 

I began writing a manual which details all the modifications, construction details and other tips necessary for someone to build and install a V2315CF for use with their own IBM 1130. The project is shared on Github along with PCB design files, Verilog and C code and other essential files, but the manual covers the essentials for putting it all together. This manual will be at least 50 pages long and may grow substantially beyond that as I validate that a reader will have all the information they need to successfully implement the project.

WAITING TO PROCEED ON OTHER TASKS

I have no response yet from Lattice about the license file I need to synthesize the FPGA logic for the V2315CF - those changes are what I must test to finish debugging the seek behavior of the project.  

I am waiting for filter and gasket materials to get the Diablo model 31 disk drive in good working order for the Diablo Archiver project to begin reading and saving the contents of the 2315 cartridges from my collection. 

I will also be tied up all day Wednesday providing a tour of Cape Canaveral Space Force Station and its historical facilities to 200 undergrad and graduate college interns, a Brigadier General and other brass in support of the Air Force Civilian Services organization. It is likely that my progress is mostly stalled until Thursday when the awaited items may be on hand and when I can get time to go back into the workshop.