Working on the disk drive, breadboarding new loader, repairing SSM 1053 and other tasks

ADDITIONAL TREATMENT OF RUST ON MODE SWITCH PLATE AND DISK PARTS

As I mentioned in a prior post, a few parts still had signs of orange-brown rust even after the prior treatments so I coated them again. A cylindrical rod that holds the disk drive covers over the mechanism was very badly pitted, as was the spindle that grabs and rotates the bottom of the disk cartridge. As well, the rotary mode switch plate wasn't completely converted so it got another shot of the Naval Jelly. 

SETTING UP BREADBOARD OF NEW MEMORY LOADER

I began setting up the central logic of the new core memory loader, the one that will trigger the 1130 cycle steal (DMA) mechanism to load memory much faster than the previous loader program. The breadboard will contain the state machine and logic to respond to both 1130 and Arduino, but not the output circuits as these are directly driven by reaching certain states. This reduced the wiring to just eight ICs, only 114 pins, and will make use of my Cadet testing platform.

There are four slide switches that will represent the key input signals:

• Arduino request for a cycle steal
• -X6 cycle steal clock stage
• -CSLevel0 which indicates when cycle steal is active
• -Stop Latch which is used to be certain the 1130 is stopped before loading

A pushbutton will simulate the fourth 1130 input signal, power on reset of the machine, to be certain that the loader will enter a good initial condition. The states are displayed on LEDs on the CADET.  When it appears to operate properly with manual switching, I will set up some rapid triggering and put a scope on the state outputs to be certain it doesn't glitch or step too rapidly. 

The loader is quite simple to interface with - when the Arduino places a 15 bit address and 16 bit data value on output pins, it raises the Arduino Request signal. It then waits for my state machine to get to the end of the cycle steal where the loader raises a Request Done signal back to the Arduino. The Arduino drops the Arduino Request line to finish the cycle. It can then assert new address and data values and request the next cycle steal. 

TESTED BLOWER MOTOR - FOUND OPEN CIRCUIT IN WINDINGS

I wired up 115VAC to the disk drive to check the operation of the blower motor, since it seems to have very crusty and stiff bearings. I wanted to see if it would spin normally and recover from the trauma it has suffered. When I applied power, absolutely nothing happened. I could see that 115V was present on the wires leading to the motor, but no action. 

Based on this finding, I decided to pull the motor, check more carefully for continuity and then disassemble it to find the cause of the failure. 

Motor out and on the bench

no obvious damage on the windings

No trauma that suggests why it failed

Stator seems intact but bearings are very bad

The motor has five wires connected to it, one is a frame ground shield inside the cable but does not connect to the motor itself. A black lead is connected to the metal motor housing and tied to the frame ground back in the AC power box. Neutral is delivered over the yellow lead and the hot side of the AC is connected to one winding all the time (blue wire) and also to a second winding (red wire) when the contactor energizes. Apparently the second winding is added when the current is high (at startup) and then switches off when the motor reaches its normal speed. 

I also see a thermal protection link in the diagram of the motor, which could be blown but it does not appear to affect the coil between the yellow and red wires at all, only the winding between yellow and blue wires. However, the yellow wire is open circuit to all the other windings. 

I checked against the drive motor, which uses a very similar circuit, and confirmed that there should be connectivity from yellow. I don't see any signs of damage to the cable that would explain the open circuit, therefore it is very likely to be inside the motor. 

If I can find and repair the open circuit, I will still need to get the bearings working better. If I can clear them up with new lubrication then it is possible to salvage this motor once the break is repaired, otherwise we are going to need a replacement motor. 

DISASSEMBLING BLOWER TO CLEAN

The drive has a blower that pulls outside air through the electronics and pushes air through a HEPA grade filter to flow between the head and disk platter. The chamber for the HEPA filter and the blower itself was packed solidly with rodent nesting materials. I wanted to get the blower apart to fully clean the chamber. We don't want residual material blowing to the filter and perhaps onto the disk surface, so it should be as clean as possible. 

As you can see with the picture below, the blades of the blower have a lot of crud remaining even after I pulled out the nesting junk. I loosened the setscrew to pull the blower off the motor shaft but due to the rust formed by exposure to urine, it is extremely challenging to remove. 

I have not been successful today in removing the blower, but will keep at it since it is necessary both for the cleaning and in the eventuality a new motor has to be installed. 

SSM 1053 REPAIR WORK

I did receive the new rotate tape today, which I verified is the proper length and in excellent condition. You can see that it is smooth and unbent.

Compare that to the old tape that snapped, shown below. You can still see a bent section, although the tape snapped at a different and presumably worse deformation. 

I also checked the repair of the SMS paddle card that provides the power connection to the 1053. It appears to be holding adequately, but still needs me to bridge across the crack with wire so that the fingers deliver power up to the wire. 

Crack affected the fingers on the right side

The right side fingers are K and L together for frame ground, M for +12V, N is also +12V but only one of the fingers is needed to provide that voltage, P is unused and Q and R together are the +48V source. The crack only impacted KL, M, N and P fingers, QR is past the crack thus has continuity. Two wires, to bridge KL and M lines, will restore this paddle card to good condition.