Rohde & Schwarz CMU200 LCD Backlight success - Page 1
Forum section: electronics / repair

author: CJay
author_rank: Super Contributor
timestamp: November 16, 2016, 04:40:30 pm
content: The backlight on my CMU200 was dim, dim enough that I need to lower the ambient lights to see it during the day so I've been using an external monitor which is workable but awkward as the softkey functions align with the screen, obviously.So, I figure the CCFLs for the backlight are worn out, it's an old piece of kit after all and has seen lots of hours use.I've been keeping an eye open for likely CCFL tubes (found an unused new HP slide scanner adapter which has two lovely CCFLs about the size I'd expect to need in it) and also weighing up the pros and cons of LED replacements.Today I finally got the time and courage to strip it down and remove the FMR5 module to see what could be done.After *lots* of non magnetic countersunk screws were removed I managed to prise the module out and strip it down to access the LCD, whereupon I realised all chances of using the CCFLs I have were zero, see the attached pic of the original CCFL removed from its plastic carrier.I could have ordered a flexible LED strip or reused one of the ones I've salvaged from smashed laptop displays, I realised that the main problem was the reflectors in the CCFL module had curled with age and were wrapped round the tube blocking almost all the light.Removing them and replacing with the reflectors from the slide scanner was a doddle and the Result was an LCD screen that's absolutely tons better and useable in bright lighting.I'll probably need to replace the tube at some future point but for now, it's all back together and working nicely.

author: Velund
author_rank: Regular Contributor
timestamp: November 28, 2016, 02:08:48 pm
content: By the way... Did you measured this ccfl? I do not see angled lamps offered for sale, so there is a chance that it will be necessary to make one from straight tube. Not sure that it is possible, though.My CMU will require serious repair anyway, before it can be used, but I do see reddish hue anyway - on a laptops it was indication of close ccfl backlight death.

author: RF_fanatic
author_rank: Regular Contributor
timestamp: December 04, 2016, 07:46:45 pm
content: Redish hue is caused by the glass with encapsulated shielding not by the electronics, its a known "bug" of many R&S screens.Replacing displays won't solve it, changing the glass does.

author: CJay
author_rank: Super Contributor
timestamp: December 05, 2016, 09:58:10 am
content: No, I didn't measure it as I figured it would be nigh on impossible to buy a replacement easily, I'd planned on using LED strip from eBay if I'd not worked out that the reflectors were causing the problem.The glass on mine has begun to change colour with a yellwish tinge around the edges giving the effect of a border but it's not affecting the readability of the screen.I believe the glass has some sort of RF shielding coating and it's that which is changing.

author: eb4eqa
author_rank: Regular Contributor
timestamp: December 27, 2016, 10:28:11 am
content: Hello,If you want to change the CCFL to LEDs, you may find this interesting:LCD LED Backlight Conversion ( Sharp LQ084V1DG21 )http://www.rbarrios.com/projects/LCD2LED/Agilent 8753ES LED Backlight Conversionhttp://www.rbarrios.com/projects/8753LED/Regards,Roberto

author: Velund
author_rank: Regular Contributor
timestamp: March 02, 2017, 09:41:28 pm
content: Quote from: CJay on December 05, 2016, 09:58:10 amFor now, I found a supplier, that offer L-shaped CCFLs of various sizes. But unable to disassemble my unit now to look for correct Sharp lamp size.http://www.iccfl.com/shaped-ccfl-tubes-c-25.htmlMaybe someone have that panel accessible and can measure original lamp?PS: Looks like it is 185 x 140mm x 2.6mm diameter, if information, provided on the following page is correct...http://www.ccflwarehouse.com/185x140x2lcc.htmlSo, iccfl.com does not have correct size...

author: Velund
author_rank: Regular Contributor
timestamp: July 09, 2017, 01:35:36 pm
content: Does anyone replaced EMI shielding glass in CMU200 recently? Is there suitable replacement that may be purchased more or less easily (maybe some industrial laptop LCD protection glass to be cut to size)?Mine is looking ugly as a scarecrow...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 09, 2017, 02:12:33 pm
content: There can be issues replacing CCFLs with LEDs on colour LCDs - sometimes the spectral peaks of the LEDs can be different to those on the RGB stripe filters.There's an article somewhere where a guy describes getting some specifically-tuned LEDs from Nichia - I think it was for a laptop, which had slightly unusual RGB filter wavelengths