Document Title: [CinematronicsVBeamRepair.html (html file)]
This should be of interest to anyone who has a Cinematronics B/W X-Y monitor (Vectorbeam) that has either died or is dying due to it's Hi-Voltage supply. The supply MUST be the 'off-board' type such as the Keltron HP160124A, this can't be done (at least not easily) with the Hi-V supply that is part of the big monitor pc board. I've also seen another supply used that does not look like the Keltron, but it's hook-ups were the same, so all this applies to it also.
The supply has three outputs: 16kV, 400VDC (FOCUS) and 90VDC (CATHODE). On several supplies that I have the 90V output will fail and drop down to about 45V. If all the normal intensity lines on your screen dissappear leaving only the high intensity lines, there's a good chance your 90V output is dying. The 90V is used in the brightness circuit which drives the Pix tube's cathode, controlling the amount of beam current, hence, picture intensity.
The failure, at least in my supplies, is due to a component within the voltage quadrupler circuit; the potted and plastic encased section of the Keltron. I haven't tried to repair one yet, it may not be possible. For now, assume it's not.
The manufacturer of these supplies, Keltron Corp. of Waltham MA, wants nothing to do with them anymore, can't blame them. The only option is to replace it. That is, if you can find one.
Another option is to replace it with a similar power supply. Not that many to choose from. What I've found is that the Electrohome G05's Hi-Voltage supply can be used as a replacement. This MUST be the older version Assy #02-160007-01 with the PC Assy #02-160008-01 Issue 5. The newer version, Assy #05-160006-01, with the PC Assy #02-160016-01 (02-160027-01 ?) will not work. The former is rated for up to 16KV where the latter is rated for 12kV (different design). The Wells-Gardner version of this supply [38A5583-000 using PCB300] is rated for 14.5KV. I've got one ready to go but I haven't tried it yet.
Connecting the Electrohome supply to the Vectorbeam it trivial. The drawback is that new mounting holes will need to be drilled in the monitor's metal side panel. The new cable needed is simple enough to show below. The only caution here is that the wire for the 400V connection MUST have an insulation rated for 600 Volts or greater.
Cinematronics Electrohome deflection bd Power Supply PCB connector Connector P900 +90V 1 <-------------------------<5 2 > +400V 3 >-------------------------<1 +25V 4 >-------------------------<8 GND 5 >-------------------------<7 6 > Chassis --------------------
Before connecting the new supply, check the voltage level of the +25V supply. The Electrohome EHT supply was designed to operate over an input voltage range of +23VDC to +38VDC but it's better to be sure. When you do power up the Hi-V supply you will probably need to adjust the anode voltage. The FOCUS voltage will also need to be adjusted to +400VDC. It's adjustable limits are -140V to +400V so definitely check it.
RESULTS: The CATHODE output voltage (and the FIXED 400V, P900-3) track the adjustment potentiometer so when you adjust the anode voltage the 90V & 400V also change. This is why I chose to use the variable FOCUS output. I have my supply set so that I get 116V, 400V and 15.4kV. If the anode voltage is set lower than 15kV the picture expands past the edges of the tube due to the slower electrons being deflected for a longer time than they should. The 116V is almost 30% higher than what the intensity circuit normally expects but the 2N5550 XSTRs which do the level switching can handle this without any problems.
I have my supply running at it's maximum output but according to it's specs it should be able to handle it. So far, I've only had the machine running for a few hours and it seems fine. Only time will tell whether this replacement will hold up.
I will assume no liability or responsibility for any damage done to any person or property if the suggestion above is followed. You had better have a good understanding of the possible hazards in doing this (hazardous voltages, pix tube implosion, etc.)