Philips CM8833-II video monitor repair - Page 1
Forum section: electronics / repair

author: steve30
author_rank: Frequent Contributor
timestamp: August 16, 2018, 02:37:23 pm
content: I was wondering if someone could advise me regarding some CRT video monitor issues.My Philips CM8833-II monitor's flyback transformer conked out a few years ago, so I replaced it with a new HR Diemen brand replacement. Fortunately the monitor worked after this replacement.The monitor seems to have a bit of an issue though. The whole picture dims a bit if you display a bright scene (e.g. a mostly white picture). This is noticeable if you try and display a dim dialog box on top of the bright picture, as the dialog box will become even dimmer still.This isn'ttoonoticeable, but I'm a bit of a perfectionist. Does anyone know what causes it? I can't remember if the monitor did it with the old flyback transformer or not.Thankssteve30.

author: johnkenyon
author_rank: Regular Contributor
timestamp: August 16, 2018, 03:28:27 pm
content: RGB or composite video input?

author: RobertPS
author_rank: Contributor
timestamp: August 16, 2018, 04:49:36 pm
content: Could be a problem with solder joints. These are getting old!Check and re-solder.This link is for a document in dutch with common faults and repair tips:http://www.bas-ditta.info/doc/Philips%20CM8833-2.pdf

author: stj
author_rank: Super Contributor
timestamp: August 16, 2018, 05:55:44 pm
content: replace the main capacitor on the B+ rail.it smooths the 100-ish v line that feeds the lopt and pretty much everything else.when it starts to fail the usual symptom is when you try to draw more current my for example, displaying a bright white screen, the image with shrink a bit or shake because of volt-drop.

author: steve30
author_rank: Frequent Contributor
timestamp: November 25, 2018, 08:28:09 pm
content: I eventually got round to looking at this again.The monitor has a 128V rail. There are two electrolytic caps smoothing this rail. I tested both and they were fine, both in terms of capacitance and ESR.The rail varies by 0.5V between a completely black screen and a completely white screen. I'm not sure how acceptable this would normally be, but it is enough to cause the picture to change slightly.

author: steve30
author_rank: Frequent Contributor
timestamp: November 26, 2018, 01:09:32 pm
content: Just wondering, would it be worth trying a bigger capacitor on the 128V rail?

author: stj
author_rank: Super Contributor
timestamp: November 26, 2018, 01:38:26 pm
content: look up the spec of the original, in this application the ripple current is key.

author: perieanuo
author_rank: Frequent Contributor
timestamp: November 27, 2018, 10:27:12 am
content: Quote from: steve30 on November 26, 2018, 01:09:32 pmA little more yes but not much.I woldn't increase more than 50%.remove the old one.and of course readjust the voltage, in theory with flyback disconnected.I was doing this only if I hadn't the original value in 'stock'.I remember when I was repairing tv's maybe your transformer wasn't correctly adjusted (focus bias and acceleration if I remember well, I was doing it based on eye impression on max luminosity)Of course dry capacitor can do same trouble but I doubt, you can see if it's diformed on his upper side in most cases.Regards,pierreEnvoyé de mon iPad en utilisant Tapatalk