Testing my new seek logic for the Virtual 2315 Cartridge Facility - part 13

ASSEMBLED NEW VERSION OF 2310 INTERFACE BOARD

The Virtual 2315 Cartridge Facility (V2315CF) has a component that is a board that interconnects the cables from the IBM 1130 disk controller logic, the internal disk drive, and the main V2315CF unit, as well as a few other functions. I adjusted the design to include electronic switches that connected the signals between the internal disk and the disk controller logic when the V2315CF is in real mode, the norm. The alternate virtual mode does not use the internal disk thus all signals flow only between the disk controller logic and the V2315CF. 

ADJUSTING THE DISK DRIVE SEEK SETTINGS

I sat down with the maintenance manual, a scope, a voltmeter and tools in order to make all the adjustments to the internal disk drive. Simply unplugging the cable from the V2315CF from the disk drive electronics put it in Customer Engineer (CE) mode where I could operate it without using software on the 1130. There are CE switches to move the arm in and out, in both 10 mil (1 cylinder) and 20 mil (2 cylinder) steps, either once per switch press or continually while the switch is held on. 

The first step is to perform a dynamic balance of the tachometer amplifier output, setting it so that there is zero output voltage while the arm is not moving. The next adjustment is for the voltage at which the mechanism stops accelerating the arm and turns off the go latch. This drops the +Access Ready signal, flips the voice coil polarity to begin slowing the arm and starts to engage the appropriate odd or even detent to lock the arm in at the target cylinder position. 

There are different target voltages for 10 mil and 20 mil, since the arm has to move farther for a 2 cylinder step and that requires a faster speed. The target voltage is compared to the voltage on a capacitor which is (dis)charged by the tachometer output, e.g. by the speed. 

A third adjustment sets the dead band, the level below which the servo does not attempt to move the arm. This is done to avoid oscillation while still providing enough oomph to properly accelerate and decelerate the arm. 

The last of the electrical adjustments is for the timer which keeps the +Access Ready signal low from when the trigger voltage stops arm acceleration until the detent should be fully engaged and the arm not moving. The target is 10 milliseconds. 

STARTED TO CHECK DISK DRIVE SETTINGS AND DISCOVERED VOLTAGE ISSUE

When I began to adjust some of the potentiometers in the disk drive I saw weird behavior. The balance was always zero, no setting of the pot would produce anything else. The oscillations never occurred when changing the dead band. These settings are all on the Amplifier card at slot F2 and F3 of the disk drive card cage. The manual suggested voltage checks at certain pins, one of which should be 8V but came up at only 6.2V. 

A QUICK CHECK OF THE INCOMING POWER RAILS TO THE DISK DRIVE FOUND ISSUE

The 1130 generates the DC voltages for the disk drive, the three main power rails as well as 48VDC. The power rails for Solid Logic Technology (SLT) are +3V, -3V and +6V. The 6V rail was only generating 5V, which is way too low for good operation. I checked back at the main logic gates of the 1130 and found that the voltage was low at that point as well. This is a definite problem for the entire system.

ADJUSTED LINEAR VOLTAGE REGULATOR TO RESTORE RAIL TO +6V

I adjusted the potentiometer on the regulator to restore the voltage to the correct level. I have no idea how this got so far out of spec. It might explain some of the odd results or intermittent issues I observed in the past month or so. 

The 1130 has a circuit that verifies the presence of all three primary voltage rails, shutting down the machine or blocking power-up if they aren't good. However, it isn't highly precise, since 5V was high enough to pass the check while still being far too low for proper operation. It is intended more to detect the lack of one of the rails, not that they are correct.