Tested regulator under load; working on power sequencing issue

OUTLET INSTALLED IN WORKSHOP

The workshop had its 230V receptacle installed today, something that was necessary to continue restoration work on the VCF 1130 system's power system. I had wanted a 30A receptacle with four wires (ground, neutral and hot lines from different phases), so that I could pull 115 or 230 depending on the wiring of the plug I insert. 

What I had mentioned earlier to the landlord was an L6-30 receptacle, which is three wire, lacking the neutral. This is a 30A 230V only outlet. That is actually fine for the work I am doing now, so I was able to proceed with my testing. 

L6-30R outlet

REGULATOR UNDER 15A LOAD FOR FINAL TEST

Now that the 230V outlet is installed in my new workshop, I could power up the VCF 1130 system to test the +3V regulator. The resistor network is installed which will draw 15A at the nominal 3V output of the regulator. It could be split to start out at 6A draw, 9A or all 15A. 

The expectation is that the voltage setting under the various load levels will be essentially the same as with no load. This ensures that the regulator is working properly. 

I powered up the 1130, with only the +3V regulator switched on. Pin A of the SMS card that sequences power was disconnected - this pin is used to shut down the machine if all three primary voltages (+3, -3 and +6) are not present within a few seconds of power-up. Since I will only be working with +3, I had to pull this wire to leave the system switched on. 

The voltage with no load was set to 3.01V and then I connected the resistors set up for a 6A load. The voltage was still 3.01V at that current which was exactly at the starting point. 

Resistors producing 0.5 ohms for 6A draw

Regulator maintains voltage at 3.01V

I changed the wiring of the resistors to draw 9A and saw 3.01V measured. Once again, holding the voltage very accurately.

Three groups of resistors for 0.33 ohms, 9A draw

Still holding at 3.01V

Finally, with the resistors wired to load the regulator to 15A, I saw the output voltage sit at 3.01Vfor at least a minute. I can declare the power supply completely repaired and working as it should. 

Resistors set for 0.2 ohms, 15A of draw

Holding exactly 3.01V

Next up I connected the logic to the voltage regulator outputs, put pin A back on the sequencing card, and then brought up the system to adjust the voltages as seen at the base of the logic gates. The specifications are:

    -3 supply      between -2.88V and -3.12V
    +6 supply     between +5.76V and +6.24V
    +3 supply     between +2.88V and +3.12V

I set the voltages to 3.01V, -3.01V and 6.01V but did notice that the machine would drop power and lock out the power switch after five seconds even though all three regulators were online and putting out the correct voltage. 

ISSUE TO DEBUG IN THE POWER SEQUENCING LOGIC

The 1130 feeds the output of the three main power regulators to three relays on an SMS card. Then the three relays are all energized, the series circuit is completed to power on relay R1 in the main power sequence box. The purpose of R1 is to switch the +12V and +48V supplies into the logic circuitry. 

However, R1 has a second purpose. If R1 is not activated by the time the 5 second time delay at power-up has finished, then pin A of the card will latch in another relay which drops power to the machine while remaining energized to remember that there was a power rail issue. The main power switch does nothing while this new relay is energized. The CE has to flip a switch or remove building power in order to reset the relay and allow another power-up attempt. 

Power validation circuit to ensure +3, -3 and +6 are present

I had verified that all the voltage rails are present and at the proper levels, but the card is no activating R1. I did a quick test of the voltage on the card pins K, M and N relative to pin C which should show the +6, -3 and +3 levels respectively. The -3 pin was reading only -1.9V but the main regulator was continuing to produce -3.01V as it had been set. 

I did some testing of the SMS card to verify that the parts are okay. Using bench power supplies I confirmed that the three relays RR2, RR3 and RR4 would latch as their respective supplies were connected. Further, I verified that the series circuit worked through the relays which should have triggered relay R1. 

SMS card with RR1, RR2, RR3 and RR4

I had to leave the workshop before I could delve further into the issue. However, since we do have good power, resolving this should be easy. While I could pull pin A off the card so that it didn't drop machine power, without relay R1 being activated we don't get the +12V and +48V supplied to the logic. Since the mode switches and pushbuttons are powered by +12V, the machine can't really be debugged until I get this section fixed. 

I did see a good state reflected on the display panel, indicating that the machine was set up properly by the power on reset and was apparently ready to do more once it had +12V active.