Results of DSKY power supply testing and power-up

TEST SETUP

The equipment I set up on the bench for the test of the power supply was:

• Signal generator set to produce 5V 800 Hz square waves
• Oscilloscope to observe and measure the outputs of power supply and signal generator
• My AGC interface board
• Dual bench power supply delivering +14 and +28 to the DSKY power supply
• VOM as a voltage level test

The interface board I build contains converter circuits between the Apollo Guidance Computer I/O levels and TTL/LVCMOS for use with modern technology. In particular, I had a circuit designed to hook to the AGC's D type inputs which was an open collector inverter gate with a pull-up to spacecraft signal levels (+28V). By leaving the 28V disconnected, it was a simple open collector that could be hooked to the DSKY power supply and accept a TTL square wave input.

BUILDING HOOKUP LEADS

In order to fit onto the Malco Mini-Wasp blade connectors on the power supply, I needed to create some wires with push-on connectors that almost fit. These don't grip really firmly but wedge on enough to make electrical connectivity. I had to crimp the connectors to many individual wires, then put heat shrink over the end to prevent shorting as the connectors can tilt and wobble.

Male Malco Mini-Wasp connectors, rectangular ended

Pin with a suitable rectangular shape to press over the Malco blade

Building jumpers between Malco pins, prior to heat shrink application

WIRING OF THE SETUP

I hooked the bench supply of +14 and +28 to the pins of the DSKY power supply. The signal generator output was wired to my interface board, whose output was hooked to the DSKY power supply input for 800Hz pulses. A put a 10K resistor across the DSKY power supply contacts for the dimmer to represent a pot set to max brightness. The DSKY supply output pins were wired to my oscilloscope where I could measure the output being produced.

As a safety precaution, I made sure that my oscilloscope ground lead wouldn't damage either the DSKY power supply or my scope. This is a quick test with a VOM from the ground lead of the scope to the planned ground attachment point in the circuit under test.

VERIFYING THE 800 HZ INPUT TO THE POWER SUPPLY

First I looked at the waveform coming from the signal generator. All was good.

Output of my signal generator

Driving this 5V signal through my interface circuit with a temporary pull up to 14V gave me a clean output signal, ensuring that I had a proper input for the DSKY power supply.

Amplified to 14V swing by my AGC interface circuit

Next I checked the output with it hooked to the DSKY power supply with +14V applied to it.  This too looked good.

VERIFYING THE OUTPUT OF THE POWER SUPPLY

I then switched on the +28V and +14V levels, watching the output signal on the VOM and oscilloscope. My scope maxes out at 50V per division, which isn't enough to show a full 275V AC signal. Still, I could set it to measure the peak to peak and other values.  I was happy to see it developing a peak to peak well over 450 volts.

Output of the power supply at full brightness on dimmer control

LIGHTING A SEGMENT OR TWO ON THE EL PANEL

I wired up the two ground pins of the Electroluminescent Panel to one side of the AC from the DSKY power supply and then applied the other side to the fixed lines and the Comp Acty pins. Nothing showed. Since I had an unexpected non-zero resistance between the two ground pins 155 and 156, I may have enough problems with the panel that it will be difficult to light it up.

Worse, the funky pins I am using are very difficult to keep connected to just the nine pins on the power supply, such that I kept losing the high voltage because one of the supply voltages, ground or the input pulses went bad.

It is time to rethink how I make the connections before I continue testing.