HP 54542C LCD display problem - Page 1
Forum section: electronics / repair

author: adilmalik
author_rank: Contributor
timestamp: April 19, 2017, 12:35:40 pm
content: HiI got my hands on an old but well looked after HP 54542C 500MHz 4 Channel Scope. Its amazing, even by today's standards!The only problem is that the screen seems to have this intermittent problem where strange lines appear across it. This usually goes away after 15 minutes and sometimes reappears etc. Does anyone have any ideas?Thanks!Link to documents:http://www.keysight.com/en/pd-1000001426%3Aepsg%3Apro-pn-54542C/4-channel-2-gsa-s-color-digitizing-oscilloscope?pm=PL&nid=-32417.536881118&cc=US&lc=eng

author: Daxxin
author_rank: Regular Contributor
timestamp: April 19, 2017, 05:54:42 pm
content: look like thermal problem loosing contact

author: adilmalik
author_rank: Contributor
timestamp: April 19, 2017, 07:09:32 pm
content: thanks for the reply. You mean with the LCDs contacts?

author: james_s
author_rank: Super Contributor
timestamp: April 19, 2017, 07:14:09 pm
content: That looks like somebody has removed the CRT and stuffed a small LCD in its place. Was this the stock display in these models? The enclosure looks identical to the HP CRT based DSOs of the era but that particular model may have been LCD to start with.Is that moire distortion in the photo or is that what the display actually looks like?

author: adilmalik
author_rank: Contributor
timestamp: April 19, 2017, 07:45:58 pm
content: This was the stock LCD from HP. I believe it was identical to the CRT series apart from the LCD. Yes the picture shows way more distortion, in reality it just has this line of pixels running along the whole LCD and poor contrast. every now and then it just goes away, usually after 15 mins.

author: james_s
author_rank: Super Contributor
timestamp: April 19, 2017, 08:06:32 pm
content: Strange, looks like somebody's home made hack, HP didn't even bother to make a new bezel for the LCD.Do the lines go all the way across? Looks to me like they don't, which implies that the problem may be in the system that creates the image rather than the display itself. Do these scopes have a VGA output on the back you could try with an external monitor? For intermittent faults like that one of my favorite techniques is to gently poke, prod and tap parts with an insulated stick and see if I can find something that reacts to my touch.

author: adilmalik
author_rank: Contributor
timestamp: April 19, 2017, 08:16:25 pm
content: Yes the lines go all the way across and are perfectly/evenly distributed. I was quite surprised to see the LCD too! At first I too thought its a DIY job. Apparently this was HPs first high end LCD scope (?)I am tempted to order a new LCD from china, although it costs £100. So I really want to be sure before I do. I measured the voltages for the LCD, they should be 12 and 5, both are present and stable.

author: james_s
author_rank: Super Contributor
timestamp: April 19, 2017, 08:21:16 pm
content: Sometimes faults like this can be repaired. I don't know what this display uses but some are connected to the driver via flexible rubber strips, and others have film ribbon cables bonded to the glass. The former can be removed, cleaned and reinstalled. The latter are a bit more tricky but I did repair several Game Boy handheld systems with a similar fault by rubbing the back of the ribbon with a soldering iron set to about 160C to re-set the conductive adhesive. A bit risky but you have little to lose in this case.I still advise trying an external monitor if that is supported, just to be completely certain that the fault is in the display. You will be upset with yourself if you damage the display trying to fix it only to realize the problem is elsewhere.

author: adilmalik
author_rank: Contributor
timestamp: April 19, 2017, 08:38:07 pm
content: Apologies,I forgot to reply to that earlier. This only has a RS232 , a parallel port and GPIB port. Not VGA

author: adilmalik
author_rank: Contributor
timestamp: April 20, 2017, 12:09:30 pm
content: Ok found the culprit, this has to be it?Finally took apart the LCD assembly and found some gunk spilled all over it! How on earth did it even get there, doesnt seem like a leaky cap, its everywhere..Any ideas on how to proceed cleaning it? Alcohol and toothbrush?

author: carl_lab
author_rank: Frequent Contributor
timestamp: April 20, 2017, 01:17:16 pm
content: Nice!The "C" model has a color LCD, the other models have monochrome CRT.Quotehttp://www.keysight.com/main/redirector.jspx?action=ref&cname=EDITORIAL&ckey=1000071138%3Aepsg%3Adow&lc=ger&cc=DE&nfr=-32417.536881118.00