Tektronix TDS684A Display issues CRT replacement with LCD has anyone done this ? - Page 1
Forum section: electronics / repair

author: radioguy123
author_rank: Regular Contributor
timestamp: October 30, 2020, 03:42:26 pm
content: I have a Tektronix TDS684A with a very dim color screen. It started out where I could see nothing. And of course it had the curdled optical coupling gel between the crt and the shutter. So I cleaned out the gel and still the image is very dim but is there.Now I am debating whether I should screw around with the crt controls ?? Adjust the brightness ? I have heard horror stories where messing withthese controls could actually damage the video chips on the main boards ? I don't know.Of course there are the VERY EXPENSIVE lcd replacement kits. I don't want to put that much money into a very old and questionable oscilloscope.I guess what I want to know is are there people out there that have replaced the color crt with inexpensive Chinese lcd and controller boards from ebay ?I realize you would need a lcd that would fit the space. And a 4:3 aspect ration. Also the lcd would have to be able to display the 640x480 video signal available at the back of the scope. Unless you are very good with electronics and can create the circuits that the kits have and take the signal from the video chips. I have been trying to contact some of these chinese vendors and truthfully they really don't know what their selling.I have found some possible candidates on ebay and will list some links here. But those links probably won't be valid for very long.https://www.ebay.com/itm/LCD-Screen-7-800x600-A070SN02-work-with-VGA-LCD-Controller-Board-KYV-N2-V2/143460478498https://www.ebay.com/itm/7-CLAA070MA0ACW-TFT-LCD-Screen-HDMI-VGA-Driver-Controller-Board-800-600-Kit-US/114307076772Both of these boards should have a VGA input. Unfortunately the controller boards have keyboards that need a button pressed to turn them on.So I don't know if once turned on will turn on again with just power on. That could be a problem.And these boards will of course need a 12vdc source. That 12vdc is hard to come by on these oscilloscopes so a dc to dc converter will be needed.Once again communicating with the vendors they didn't provide any useful information.So just reaching out there for some useful information.thanks

author: CaptDon
author_rank: Super Contributor
timestamp: October 30, 2020, 06:18:32 pm
content: If the scope is in nice condition it may be worth buying the kit madespecifically to replace the CRT screen. There are also a lot of pulledout CRT/Shutter units on Ebay which would be plug and play. The CRT'screen' controls can be accessed through some small holes about 1/3of the way back on the left side after you remove the case. There is aCRT 'brightness' bias adjust there. The CRT is monochrome with a colorshutter. The scope in good condition is worth about $500 typically. Ifyou have never replaced the Dallas 'ramified timekeeper' and/or theNVRAM it is probably time to do that. Buy the kit from the Ebay guyfor around $100. He is top shelf and can most likely pre-program thechipset for you. I did my scopes with his kit and stand with him 100%.

author: james_s
author_rank: Super Contributor
timestamp: October 30, 2020, 06:23:39 pm
content: I love those NuColor displays, although they drive the tube hard to make up for the light lost to the shutter which is pretty substantial, the result being the tubes wear out much faster than a comparable monochrome display. If it's already unusable it's worth trying to turn up the screen control a bit, or even try a CRT rejuvenator although the result of those is spotty, especially with the thin-neck tubes these displays use. I think the cathode is so small that there is not a lot of extra material on it to begin with.

author: radioguy123
author_rank: Regular Contributor
timestamp: October 30, 2020, 07:48:31 pm
content: So none of the crt controls on the side there are going to endanger the other video chips on the main boardsDid anyone look at the ebay lcd's in my links ? Has anyone tried anything with these LCD's ?I agree about the NVRAM that should be replaced. But only if the scope is usable otherwise. As is it is NOT usable unless I attach an external monitor.Captdon I'm only seeing a couple crt's out on ebay right now. Being sold by kellyjo guy that also sells the nvram replacement. Are you seeing something that I'm not seeing ?? His crt's are selling for about $175. I'd almost rather go with the lcd's then pay that much.James didn't you make some nvrams designed by cuebus ? How did they turn out ? Is he going to sell them as kits ?

author: james_s
author_rank: Super Contributor
timestamp: October 31, 2020, 05:59:14 am
content: I didn't look at the LCDs, the CRT in my scope is in good shape. I'd gladly pay $175 for a good CRT vs LCD, I think the novel display getting color from a monochrome CRT with no shadow mask is one of the coolest aspects about these scopes. Your post is the first I've heard of a monitor being damaged by twiddling with the controls, YMMV but mine didn't blow up when I adjusted it.I built the NVRAM chips from scratch using his PCB files. I don't know if anyone sells kits of his layout although there is an ebay seller that is/was offering somilar parts. It was pretty easy to build them though, there are only a few parts on each one. The RTC is a Dallas IC that is not normally available so I had to buy that from a China seller but what they sent me is legit and works perfectly.

author: radioguy123
author_rank: Regular Contributor
timestamp: October 31, 2020, 01:39:04 pm
content: Hi JamesTekhobbycap mentions the possibility of damaging the video board if you adjust incorrectly in his video here:I have been watching the thread on making these nvram boards.

author: Rollin Hand
author_rank: Regular Contributor
timestamp: October 31, 2020, 02:31:07 pm
content: I dont thinl the 7" lcd will fit as replacement ,more the 6.5" lcd will work.The ability to read a wiring diagram and visualise it against what is in front of you is priceless, not many people "have it"

author: radioguy123
author_rank: Regular Contributor
timestamp: October 31, 2020, 10:03:37 pm
content: Rollin Hand that is a 7" diagonal lcd. Their actual display area is 5.60" x 4.18".