CRT Input Question - Page 1
Forum section: electronics / projects

author: joel16
author_rank: Contributor
timestamp: May 23, 2025, 11:39:53 am
content: I have a CRT with controller board that I pulled from a Lecroy scope. The inputs are labeled HD, Video, and VD. HD and VD sound like horizontal and vertical deflection, but what would be expected on the video input? And I assume the brightness connections just go to a 100k pot?Now that I am thinking about it maybe HD and VD are outputs, and I need to spend some time reverse engineering the circuit.Thanks for the help.

author: moffy
author_rank: Super Contributor
timestamp: May 23, 2025, 11:58:17 am
content: I would assume that they are inputs with the video being the pixel values for each line as they are swept.

author: inse
author_rank: Super Contributor
timestamp: May 23, 2025, 12:01:01 pm
content: Can you show where the yokes are connected?

author: inse
author_rank: Super Contributor
timestamp: May 23, 2025, 12:05:31 pm
content: I guess HD and VD might be sync inputs as there is probably less logic on board.The question is what video standard this will accept NTSC, Hercules, CGA.How old is the board?

author: joel16
author_rank: Contributor
timestamp: May 23, 2025, 12:29:25 pm
content: I confirm where the yokes are connected later.I believe it is from late 1990's.

author: tggzzz
author_rank: Super Contributor
timestamp: May 23, 2025, 01:29:48 pm
content: Quote from: joel16 on May 23, 2025, 11:39:53 amWhich LeCroy scope? What can you see in the service manual? Was it working when you removed it?

author: Grandchuck
author_rank: Super Contributor
timestamp: May 23, 2025, 01:30:08 pm
content: Z axis modulation input?

author: joel16
author_rank: Contributor
timestamp: May 23, 2025, 01:57:22 pm
content: I do not remember which scope- the mobo had some bad corrosion and I scrapped all but the CRT stuff.I also do not know what model. I could only find minimal information about it, no user or service manual. It was four channel with an orange CRT and floppy.It looks like there may not be a straightforward answer, so I will have to reverse engineer the circuit for better understanding.

author: tggzzz
author_rank: Super Contributor
timestamp: May 23, 2025, 02:34:07 pm
content: Quote from: joel16 on May 23, 2025, 01:57:22 pmBest you can do is look at pictures to see if you can identify the scope range, then see if you can find a service manual for that range. I know the AM93xx had orange CRTs, since I had one before I sold it.Personally it I wasn't sure the remnants would work, I would find something else to do with my life. Debugging both the board and your understanding of the board is not trivial.

author: joel16
author_rank: Contributor
timestamp: May 23, 2025, 02:35:13 pm
content: Doing some googling it appears that the scope was an LS-140. I am able to find schematics, but they do not include the display section.

author: tggzzz
author_rank: Super Contributor
timestamp: May 23, 2025, 02:42:48 pm
content: Quote from: joel16 on May 23, 2025, 02:35:13 pmThere may be other hints in the manual, e.g. what's on the two connectors and what drives them.

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2025, 06:30:30 pm
content: Quote from: joel16 on May 23, 2025, 02:35:13 pmI doubt it. AFAIK, the LS-140 has an LCD display.

author: factory
author_rank: Super Contributor
timestamp: May 23, 2025, 07:15:57 pm
content: The edge connector seems to be similar or the same as that used on industrial open frame monitors, sometimes found used with old CNC machines, see post #2 here for the pinout;https://www.vintage-radio.net/forum/showthread.php?t=218350David

author: CaptDon
author_rank: Super Contributor
timestamp: May 23, 2025, 07:18:52 pm
content: INSE, look at the board, the yoke plugs in to the connector marked DY. The difference between Video connection and VD connection is that Video may be a pure analog signal and the VD could be digital data such as the 'on screen' vertical and horizontal sweep and gain settings of the front panel knobs.

author: m k
author_rank: Super Contributor
timestamp: May 23, 2025, 07:49:19 pm
content: Four pin Molex above flyback can be for the neck.F and G for focus and grid.Picture from under side would be revealing.What says the text near the right edge?

author: inse
author_rank: Super Contributor
timestamp: May 23, 2025, 08:39:20 pm
content: Quote from: CaptDon on May 23, 2025, 07:18:52 pmYou‘re right, I missed that

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2025, 09:33:37 pm
content: Why are yokes in the discussion here?It's a 'scope, so I'd expect plate deflection. Also, I miss circuitry on the board for a yoke deflection system.

author: factory
author_rank: Super Contributor
timestamp: May 23, 2025, 09:51:12 pm
content: It's more recent than that, a Lecroy digital storage scope of some kind, the monitor section is a bought in part, see the link in reply #12 for input connections, VD is vertical drive (aka vertical sync) and HD is horizontal drive (aka horizontal sync), both are TTL level inputs.David

author: jmelson
author_rank: Super Contributor
timestamp: May 23, 2025, 11:40:02 pm
content: The board says Eversonic, that is apparently who made the video monitor. Possibly that might get you to a schematic and spec sheet.Jon

author: CaptDon
author_rank: Super Contributor
timestamp: May 24, 2025, 01:35:45 pm
content: Benta, It's obviously for a raster scan C.R.T. system. Vertical is done with a single I.C. and horizontal is integrated into the flyback system. DY IS the Deflection Yoke connection. I am surprised the 'neck board' isn't hard wired to the board the O.P. has pictured. Some of the older HP digital scopes were raster scan with a P31 green screen. P31 is a very efficient green phosphor.

author: CaptDon
author_rank: Super Contributor
timestamp: May 24, 2025, 01:47:38 pm
content: V. Hold, V Size, and V Lin plus the I.C. with the copper heatsink right next to the vertical controls is a dead give-away of raster scan and a yoke. And VD for Vertical Drive is 100% correct assumption. The sweep rates could be proprietary, however I would first assume a standard NTSC or possibly PAL sweep frequency since those monitors are an off the shelf item made by about 20 different manufacturers.

author: joel16
author_rank: Contributor
timestamp: May 27, 2025, 11:58:15 am
content: This is very helpful, thanks everyone. Because I have easy access to an NTSC signal generator (DVD player), should I make a sync separator and see if that generates something usable?

author: inse
author_rank: Super Contributor
timestamp: May 27, 2025, 12:20:24 pm
content: I just wonder whether it will accept interlaced NTSC video or a progressive format for long persistence phosphor CRT.Maybe more something derived from computer graphics systems.What is your motivation to bring the tube back into operation?

author: joel16
author_rank: Contributor
timestamp: May 27, 2025, 01:36:15 pm
content: My motivation is a desire to learn. I do not have any practical use for this.

author: inse
author_rank: Super Contributor
timestamp: May 27, 2025, 04:18:03 pm
content: Then give it a try with the DVD player - LM1881 is your friend