Vertical shadow ghost lines on a CRT display - Page 1
Forum section: electronics / repair

author: tohtorizorro
author_rank: Contributor
timestamp: April 22, 2025, 11:13:17 am
content: Hi,A friend of mine bought a Samsung SyncMaster 735 17’’ CRT monitor that looks like it could’ve just come out of the box — but the screen has an issue. Vertical sharp contrast edges and lines cast faint “shadow” lines to their right. For example, if you display thin enough black lines on a white background, those shadows even seem to “echo” onwards, as if a signal was ringing.He suspected a capacitor issue and asked me to recap the electrolytics, which I did, but the problem remained unchanged.The monitor’s menu has a decent number of picture adjustment options, but none of them affected the ghost lines — except when changing the input voltage setting to the higher of the two available values (can’t recall the exact voltages). When set to the higher input voltage — meaning the monitor expects a higher voltage signal — the screen gets dimmer, and the ghosting becomes slightly less noticeable. Lowering brightness also reduces the ghosting a bit, but even after compensating with brightness, the higher input voltage setting seems to make the artifacts slightly less pronounced overall.There’s a fairly comprehensive service manual available online, which I’ve added as an attachment and here's a short youtube video where I try to demonstrate the issue — it's hard to capture on camera, but if you look at the vertical lines around the middle of the screen, you can see faint ghosting lines to the right which multiply when the test grid is zoomed out:One cap on the main board — a 2.2μF/50V — was listed as 4.7μF/50V in the service manual. I tried replacing it with both values but no change.I’d appreciate any thoughts on locating the cause? If it’s going to involve a lot of probing inside a live CRT-monitor I might just pass this one on though 🙂

author: CaptDon
author_rank: Super Contributor
timestamp: April 22, 2025, 09:55:44 pm
content: It truly does look like cable ringing. Funny how every amateur hack goes straight to the capacitors as the problem? Looks like an impedance mis-match causing reflections in the video cable. I wonder if the monitor includes a way to turn the termination resistors on or off? The monitor should show the correct load impedance which I think is 75 ohms in this case. You may be able to test this by proving that the monitor itself shows a 75 ohm load on each of the video signal inputs. Some monitors used a 'peaking' circuit to boost high frequency video response and those circuits do indeed show ringing artifacts. Seen as a shadow to the right hand side of a sharp transistion which indeed proves overshoot a.k.a. ringing.

author: Haenk
author_rank: Super Contributor
timestamp: April 23, 2025, 04:55:24 am
content: cr*ap cable was my first idea, however it seems like this monitor uses a fixed cabling, so there is no easy way to replace it...And one should not forget: This was very common for analog (VGA) displays, especially on budget devices like this Samsung one. There was a reason for using 13W3 or BNC on professional displays...Likely most people don't know or remember, how bad a standard CRT was, compared to modern digitally driven displays. I even remember fiddling around for an hour on our first LCD (Nokia), which came with VGA - impossible to adjust to a halfway sharp picture, even worse on our second LCD (ESCOM? 17" - amazingly cheap at that time).

author: darkspr1te
author_rank: Frequent Contributor
timestamp: April 23, 2025, 07:21:40 am
content: Have a look on the flyback transformer for a focus and voltage (brightness ) controls , many newer ones did not have them but worth a check. be carefull and turn slow, turning voltage up too high can burn the screen permanently.In the service manual it mentions trouble shooting section , have you gone through it ?I cant see from your video but it sounds like a voltage issue, which is controlled via IC101 and IC102 and the associated caps tied to the RGB and deflection side.just my 2 centsdarkspr1te

author: Rafiki
author_rank: Contributor
timestamp: April 23, 2025, 01:34:38 pm
content: Basic question, which resolution (timings) did you use for your tests? It seems you should drive with 1024x768 @ 85Hz refresh rate. Often such CRTs are adjusted for one operating point. If done for 85Hz don't expect perfect picture with 75Hz or 90Hz.Other pitfall which comes to mind - modern graphic cards/motherboards are for sure not trimmed for best analog (VGA) picture quality. Do you test with an old trusted card like Matrox Millenium or such?

author: tohtorizorro
author_rank: Contributor
timestamp: April 23, 2025, 09:26:52 pm
content: Hey, thanks for all the input. The cable was mentioned in other similar threads also but as Haenk pointed out, on this model it is fixed and a bit laborious to replace since it branches to two connectors and would require ordering parts and crimping tools. Another thing that I forgot to mention is that I did try adjusting the focus pots in the flyback transformer (I believe it has a pot for X and Y each) but it dind't seem to affect the ghosting lines.I have glanced through the troubleshooting section through but my understanding on CRTs is so frail that even the titles of the symptoms seem gibberish. "Visible retrace" sounded potentially relevant at first but then again so might have "H_Deflection failure", "S_Correction failure" or "Micom failure" if I knew what they meant.There is a plastic adjustment panel that has 5 phillips head knobs with cryptic markings (Yv, G/D, YH, YHc, Yv-s) that I believe to be for (dynamic?) convergence adjustment. Haven't touched them yet since I thought they were just mechanical screws adjusting some magnets etc. but it seems there might be a small PCB inside. Could adjusting these help the ghosting problem even in theory?I'm kind of ready to let this one go but feel bad for the owner who's spent money on parts alone without any sort of improvement. He's a nice guy and I'd gladly give him some good news.

author: tohtorizorro
author_rank: Contributor
timestamp: April 23, 2025, 10:16:54 pm
content: Quote from: Rafiki on April 23, 2025, 01:34:38 pmI've only connected the display to my laptop (from around 2015, still has a VGA connector) and just accepted the refresh rate Windows had to offer but can't remember what it was right now. 1024x768 sounds about right but I have to check this too. The owner on the other hand has tried the display with several computers (same issue with all) including some sort of retro build which probably has a compatible video card since this was to be the main display of such setup. He likely has tried different referesh rates but still, I need to look more into this. Thanks!

author: darkspr1te
author_rank: Frequent Contributor
timestamp: April 24, 2025, 07:06:11 am
content: those plastic dials are convergence adjustments (over and above the electronic options) , make sure you use a plastic tool to adjust as metal can cause interference.https://www.reddit.com/r/crtgaming/comments/ijoj5k/vga_monitor_what_does_yvs_yhc_yh_yv_mean_on_this/darkspr1te