HP8563E DIY Cathode ray tube tester-How? - Page 1
Forum section: electronics / repair

author: djsb
author_rank: Super Contributor
timestamp: December 18, 2021, 10:36:43 am
content: I'd like to ask for help on this forum before I try the HP-Agilent-Keysight-equipment IO group.I want to test if the voltages are present on the pins of the CRT on my HP8563E spectrum analyser. Maybe small neon bulbs could be used to indicate if the EHT (up to 10KV) are present on the 14 pin CRT socket. I would need series resistors to drop the voltage for the neon bulbs (assuming they work at around 240v AC). I am not familiar with CRT sockets so would like to know if they are generally available or if this one is HP/Agilent specific (I will post a photo later-Schematic of CRT driver below). I need to know if the driver is supplying the pins properly or if I have a broken CRT (it does NOT have ANY sign of life at the moment). Likewise, some kind of indicator would help me diagnose if the A6A1 HV supply is faulty. I have recapped the main power supply, and I've designed a dummy load PCB which is on its way from Aisler. I also have a High voltage probe but can't get access to the pins on the CRT.I want to explore this before I spend money on a TFT replacement for the CRT. Hope someone can advise me. Thanks.

author: m3vuv
author_rank: Super Contributor
timestamp: December 18, 2021, 12:51:24 pm
content: if i remember neon bulbs trigger at about 100v and stay lit untill around 70v ish,hope this helps,do you just want to see if there is voltage on the crt pins,or test the current they are drawing?.

author: djsb
author_rank: Super Contributor
timestamp: December 18, 2021, 01:14:56 pm
content: I just want a basic GO-NO GO test initially. I can make a custom PCB with test points on it and a few wire links for testing current if needed.

author: m3vuv
author_rank: Super Contributor
timestamp: December 18, 2021, 02:37:12 pm
content: can you not solder some wires from where the crt socket cable joins the mainboard and measure from those?,im not familliar with this but assume the socket from the crt connects to a ribbon cable?

author: RoV
author_rank: Regular Contributor
timestamp: December 18, 2021, 03:23:25 pm
content: I didn't think TFT replacement were available for vector graphics models like that. Are they?

author: djsb
author_rank: Super Contributor
timestamp: December 18, 2021, 03:44:50 pm
content: Herehttps://www.simmconnlabs.com/andhttps://www.simmconnlabs.com/1401/2522.html

author: CaptDon
author_rank: Super Contributor
timestamp: December 18, 2021, 06:55:49 pm
content: If you can get to the socket to operate neon bulbs adapters you can surely get there to measure voltages with your meter. You are making the simple into a difficult project. A difference of voltage between cathode and grid one of just 20 volts could go from zero brightness to full brightness. How will your neon lamps tell you if the K to G1 voltage is correct to light the screen? You are still going to have to verify the approximate high voltage to the final anode and so forth. I am afraid you will probably 'impair' the unit rather than repair the unit if you get your resistor loads wrong. The focus dividers and so forth are known to fail and don't appreciate arc overs and undue stress. There should be some test points for the crt cathode voltage which would be may -1000 to -1500 below chassis ground.

author: floobydust
author_rank: Super Contributor
timestamp: December 18, 2021, 08:06:31 pm
content: I would just make a poor man's HV probe, that way you can actually measure the voltages. A neon lamp would still need a HV resistor, and if it's lit it doesn't say much.Low costOhmite Slim Moxsay 1-2GIG ohm at 20kV like SLIM-MOX10803. Put it in a plastic tube/pipe/pen etc., use a double-ground clip (two wires in case of a bad day) and I do math based upon my multimeter's input resistance as a voltage divider.I did not see the HP8563 HV power supply and multiplier schematic, it might actually already use a HV divider resistor for feedback/regulation of the HV.So you can just measure that voltage node to deduce CRT anode voltage.

author: djsb
author_rank: Super Contributor
timestamp: December 18, 2021, 09:11:17 pm
content: I might try some nixie tube socket pins soldered onto a PCB (using modelling clay + trial and error + vernier caliper to get the pin spacing correct) with tracks leading to pins on the outside edge of the board. I can insert this in-between the CRT tube and the plug and use my HV probe to measure the voltages on each of the 14 pins. At least it's something to try out. There are no accessible test points that I can see or that are safe to reach. Or maybe I am making things more difficult for myself and there is an obvious and simple way that I'm missing.PS I have some piercing probes but I don't want to damage any cable insulation as this will encourage possible voltage arching.

author: floobydust
author_rank: Super Contributor
timestamp: December 18, 2021, 10:03:16 pm
content: I'd keep it simple and leave the CRT and socket alone. You just have to measure for -2.5kV and +10kV presence. CRT's only need a handful of voltages to light.The entire cathode-end is floating at -2.5kV so once you realize that, it's easier to troubleshoot a scope and not get zapped.Another approach is to measure other (safe) voltages such as the 110VDC rail at TP405 will tell you if the inverter is working.The CRT filaments should glow if the 6VAC is present, and the 10kV will make a little crackle on power on/off.If the HV is low or missing, test the A6A1 HV flyback/multiplier module, on the bench injecting even 1VAC 30kHz sine-wave you can measure proportionately lower output voltages but find a shorted diode etc.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 19, 2021, 10:43:54 pm
content: To test the CRT you could find an old TV picture tube tester. Make sure you have the correct adapter or make one. They usually come with several adapers for different size and pin configuration.You already have the pin out of your tube.I just gave away a nice one and I have access to some other testers.

author: djsb
author_rank: Super Contributor
timestamp: December 20, 2021, 05:26:57 am
content: Which tester would you recommend? Thanks.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 21, 2021, 10:49:04 pm
content: Since you are in UK and I am only familiar with US produced testers, I guess I do not know. Any of the TV tube testers here like the Sencor are just OK. Important thing is to get one with a lot of adapters so you can have one that fits your tube, Then make sure the pinout is appropriate (Heater pin, etc...). Some folks have changed the pinout to adapt to even oscilloscope CRTThese things are cheap, very little use for them today.Wally

author: BrokenYugo
author_rank: Super Contributor
timestamp: December 22, 2021, 12:57:45 am
content: Hop on ebay or what have you and get a HV probe if you want to probe the HV supplies. For what you'll have into the parts to properly rig something up with neons or build your own probe you'll be at least halfway there anyway. There are a lot out there in the 30-40kV range left over from the color CRT TV days, some are even self contained with their own meter.