LCD shuttered CRT (Tektronix TFP2A fibermaster otdr) - Page 1
Forum section: electronics / repair

author: veedub565
author_rank: Frequent Contributor
timestamp: October 16, 2015, 07:31:08 pm
content: Hi,Does anybody have experience of LCD shuttered CRT's ? specifically the type as may be used in some old color Tektronix equipment ? just wondering if there is any common problems.I have one which I suspect may be duff, it sometimes works, but then lines start appearing across the screen and then the screen sort of freezes (but the equipment is working ok)Other times the equipment boots up normally (as far as I can tell) but the screen stays a solid red color.Haven't really delved into it yet but guessing it could be some sort of control issue or a failed LCD/CRT (the LCD is bonded on isn't it)

author: tautech
author_rank: Super Contributor
timestamp: October 16, 2015, 07:43:11 pm
content: Can you edit your thread title to include the Tek model #, you might be better noticed then.IIRC nctnico has played in this field.

author: veedub565
author_rank: Frequent Contributor
timestamp: October 16, 2015, 07:57:13 pm
content: Done, from what I've read I think this type of screen is used on quite a few Tek products though, and probably other manufacturers too so just looking for a bit of general info really.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 16, 2015, 08:17:21 pm
content: ISTR someone makes a LCD retrofit kit for these

author: MadTux
author_rank: Frequent Contributor
timestamp: October 17, 2015, 01:49:31 am
content: Quote from: mikeselectricstuff on October 16, 2015, 08:17:21 pmSame guys that make LCD retrofits for HP 8566/8568. But if the Tek scope ones cost the same as those for 8566/8568, you probably don't want to buy them.http://www.simmconnlabs.com/2001/9001.htmlI also have a Tek 784 with damaged LCD in storage somewhere. IMO, the LCD/CRT combo really sucks. Drawbacks of both technologies combined. A LCD that is prone to mechanical damage combined with size, weight, HV, cathode degradation, phosphor burning and all those troubles you sometimes get with old CRTs.BTW, you don't want to try to change that LCD. There is some slimy gel in the back of the LCD (used for opticical diffraction matching). Once you try to remove the LCD, it will draw air between LCD and CRT which you will never be able to remove completely again => silly air bubbles between LCD and CRT which will annoy you even more than an occasional bad line on LCD.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 17, 2015, 04:45:20 am
content: Quote from: MadTux on October 17, 2015, 01:49:31 amIt can be done,& the LCD/CRT setup operates OK without the gel.Jose,who sometimes posts on this forum has a write-up,here:-http://jvgavila.com/tds524a.htm

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 17, 2015, 08:53:30 am
content: Quote from: MadTux on October 17, 2015, 01:49:31 amhttp://simmconnlabscom.ipage.com/store/page5.html$250/$350 mono/colour - seems pretty reasonable.

author: nctnico
author_rank: Super Contributor
timestamp: October 17, 2015, 09:54:44 am
content: Quote from: veedub565 on October 16, 2015, 07:31:08 pmWhat do you mean by solid red? Does the display still show all the text and are the controls working? You still see text/lines changing when you turn knobs/press buttons on the instrument?

author: veedub565
author_rank: Frequent Contributor
timestamp: October 17, 2015, 04:07:24 pm
content: Yeah I saw those conversion kits, look like a good option if indeed it is the CRT/LCD shutter that has gone faulty.When I say it solid Red I mean the display is totally solid Red, there is no text or anything displayed. The rest of the equipment seems to be working, just not displaying anything (apart from a (dark) Red screen) This only happens sometimes though, other times it does display normally for a while and then odd lines start appearing and when you switch to a different menu the old menu is still left displayed underneath the old one and the display becomes unreadable.So it could also be a processor/display driver/memory issue I guess rather than an actually fault with the shuttered display. I'm not sure what a failed shuttered display would look like though, I've never come accross one before.

author: nctnico
author_rank: Super Contributor
timestamp: October 17, 2015, 05:40:38 pm
content: I think the display + shutter is OK if you can get different colors. If what you see is garbled video the problem is most likely in the CPU board. Check with an external monitor to make sure. On the older models the video system works in an obfustigated way but I think your scope also works this way.First the image is composed from 2 sources: the acquisition hardware and the CPU which results in 60fps video in VGA format (640x480). The output for the external VGA monitor comes from a RAMDAC which is fed from this source. Next the color image for the screen is made by upsampling the video data to 180fps (3x60) where the red, green and blue 'components' are seperated into 3 consequtive frames making 60 Hz again.Again: first check with an external monitor first to see if the video data is right in the first stage.

author: veedub565
author_rank: Frequent Contributor
timestamp: October 19, 2015, 08:48:54 am
content: Thanks for the info, interesting to find how it works. Unfortunately there is no external video out on this piece of kit.Had a bit more of a delve into this today, voltages on the CRT look ok except for G2 which is too high effectively turning the tube off (or brightness right down whichever you prefer) So I'm going to try exploring that avenue.Shining a torch on the front shows the LCD shutter is doing stuff, so looks like a CRT control issue. Will keep you posted