Preface: I'm not sure if I should create a new thread for this or add it to an existing one. I can see there are a lot of different threads on the 576. I'll just keep this update here since I don't have a repair question about it... yet.
Well it arrived yesterday! I almost had a heart attack when I saw the package - the side of the box was torn open. But fortunately, they did pack it with plenty of bubble wrap. It arrived in the condition as advertised; better than I anticipated actually! Visually it looks in great shape. A few issues I noticed immediately:
-The max peak power/watts knob: plastic ring with power settings has separated from the knob. Will have to glue it back to it once I find the correct orientation.
-The HV protected cover is missing and the interlock switch was stuck in the pressed down position
-Springs on the Step Family and Rate gang switches are either stuck or do not stay depressed
But other than that, everything looks pretty good! CRT works! I started putting it through the 'First Time Operation' steps via the service manual. It seemed to be responding to the settings normally. I've never used one of these before so I'm kind of learning as I go. I began finding issues as I started learning more about the unit's function.
1) The HV safety interlock was engaged so I needed to find how to disable it without the protected cover. So I removed the standard test fixture to get a closer look. That's when I noticed a resistor on the terminal selector switch was literally snapped in half (I believe its R376, a 22ohm). So I replaced that.
2) I continued looking into how to bypass the HV interlock. The service manual I found provides a procedure for disabling it by soldering some jumpers to the J300 connector. But that is buried deep in the unit. So I decided to see if there was another way. I started looking at the actual HV interlock switch which for my unit is on a small PCB that is screwed to the underside of the test fixture (interestingly all the other PCBs on the unit state copyright 1968, but this little PCB says 1985. Maybe this test fixture is from a newer unit?). Anyway, the switch that is triggered by the protection cover is a Motorola MOC70W2 which I actually found a datasheet for. It is a U slotted photoelectric sensor. It has two infrared emitting diodes on one side and two phototransistors on the other. This MOC70W2 clearly was faulty - I tested it out-of-circuit and verified that. Plus, as I said, the switch was stuck in the depressed position and it still would not disable the HV interlock. The MOC70W2 is glued to an actuator that passes through the U slot - I had to remove it to get a better idea of how it worked. For my mod, I removed the MOC70W2 from the little PCB. I soldered in two red LEDs on the cathode/anode/cathode anode side (not sure if the LEDs are necessary
). And then two NPN transistors on the emitter/collector/emitter/collector side with their bases connected between the series connection of the LEDs (I suppose you could use diodes instead of transistors). Reassembled everything and it worked perfectly! Granted, I would like to find something to cover the test fixture during high voltage testing for safety purposes, but if anyone is looking for a simple bypass mod, this worked great! Also, the red LEDs look kinda cool shining thru the test fixture inputs
Next I tested a resistor and a diode - I observed the correct IV curves for both of them! So this thing is definitely showing signs of life! This is as far as I got, but I will keep troubleshooting/testing/repairing as I continue to investigate this gem! Photos attached below!