Running IBM disk diagnostic 309 against the Virtual 2315 Cartridge Facility - part 9

ANNOYANCE - THE +6V REGULATOR TRIPS ITS CIRCUIT BREAKER WHEN WARM

There have been lingering problems where the circuit breaker on the voltage regulator module for the +6V supply will trip off as if it had overcurrent. This often happens when the machine has been running for a while, is shut off and then turned back on within a couple of minutes. 

I hooked wires to the load resistor inside the regulator which senses the full current flowing out of the regulator. It is nominally 0.072 ohms and the voltage drop across it should tell me the current being drawn out of the regulator. If it is 1.728V or less when the 1130 system is not drawing more than the 24A capacity of the regulator - that would indicate that the circuit breaker itself is weakened and needs replacement. If the sensed voltage is higher then I have to find the components drawing excess power and repair them. 

My voltmeter showed a consistent .607V drop across the resistor. I had verified that the resistor was just over 0.07 ohms using a sensitive ohmmeter, thus Ohms Law indicates the current being consumed by the 1130 system was fairly steady at just under 8.5 amperes. 

This tells me that the circuit breaker is very likely to be faulty. The regulator would need to be consuming more than 200W for the CB to be near its limit yet the system draw of 8.5A regulated to 6V is only a quarter of that. The regulator can't be that inefficient. The unregulated input power is a bit over 8V thus it should be in the 70% or higher efficiency range. 

I ordered a replacement - not an exact copy but should be able to fit it into the regulator in place of the original breaker. 

HALTED DIAGNOSTIC ON FIRST ERROR - DRIVE IS INDEED SEEKING TO 196

The diagnostic program begins by seeking backwards to the home cylinder, which is indicated by a microswitch on the drive that signals when the arm is at cylinder 0. It then issues a seek of xC7 - 199 cylinders forward. The seek ends with the arm stopped at cylinder 196 which is consistent with the data my V2315CF returns when a sector is read after the seek. This means we either have a controller unit logic defect in the 1130 or a diagnostic program error. 

DID A SINGLE XIO SEEK FROM HOME FOR 199 CYLINDERS

I then hand coded an XIO to seek 199 cylinders from the starting (home) position. In this case, the arm correctly stopped at 199, not 196. I have to validate that the diagnostic program is issuing the correct XIO seek command. I will load the program into core and then stick in a wait instruction right after it has prepared the IOCC for the seek and before the actual XIO is issued. 

I can examine what was generated and then let the program continue to issue the seek and evaluate the outcome. This should permit me to point the finger of blame at diagnostic or controller logic.