Re: 465M: No trace, No +5V, No +95V

Harvey White

Generally, you look at the inputs to the regulator inputs first, that's the bulk supplies.

Problems there can likely be a bad capacitor or open diodes in the rectifier (this assumes a non-switching style of supply).

Then you look at each of the regulator outputs and work back.  If possible, disconnect the rest of the scope from the power supply (this works if the supplies are linear, as they are likely to be), and then test.

Typically, the most obvious fault is a shorted tantalum capacitor (which are prone to shorting).  This pulls down a supply and causes trouble.

One possibility is to disconnect the high voltage (there may be a fuse to remove), and if the 95 volts is being loaded by the high voltage supply, this will let the +95 come back up.  Check across the current limiting sense resistors for excessive voltage to see if the supply is current limiting due to a short on the output.

On the neon lamps, they are there as protective devices, to limit the voltage across a circuit to the lamp's firing voltage.  I have not seen them normally on, but they can flash on power on startup and turnoff as voltages at that times can vary a lot.

Others will have more focused advice, this is general.


On 8/8/2020 9:07 AM, @HHSIII wrote:
Am using an Air Force Service Manual (Operation and Maintenance) that I found on line as my reference. When powered up the +5V TP reads -.742 (basically zero) and the +95 TP reads +5.71V. I thought I had an issue with transistor Q742 ((Figure FO-10, PS and Interface board) and zener diode CR582 (Figure FO-9 CRT and Z Axis). Replaced both of them with no positive results. Still struggling to figure out where to go from here. Any guidance, advice or suggestion will be most appreciated.
Second question; In the power supply area (Figure FO-9 CRT and Z Axis) there are two Glow Lamps DS563 and DX564. What is the purpose of these lamps? They seem to be across pins 4 & 9 of the HV Multiplier. Do they function like a fuse? If so can they be tested like a fuse? Thank you.

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