Display problem with Anritsu MS2665C spectrum analyzer - Page 1
Forum section: electronics / repair

author: jdomenech
author_rank: Newbie
timestamp: August 13, 2025, 10:03:06 pm
content: Hello everyone!My first post here. Please be gentleI bought anAnritsu MS2665Ca while ago (similar chassis to the MS2667C and MS2668C) with what initially seemed to be the classic screen problem for these devices. The analyzer works fine (I can use it through its Composite Video output) but its screen was completely blank. Getting a new screen and problem solved I thought...Current status of the repair:After putting some pieces together (see the History below) I have a screen that seems to work but it is barely visible. Playing a bit with the angle I can see a bit of the contents of the image but it is completely unusable. See image:Any idea of what of what can cause this?My theory is that it has something to do with the peculiar way this device controls the brightness of the screen. According thethe service manualit does "something" on the RGB signals themselves. See screenshot below:Something that reinforces this theory is that the instrument menus give you the option to select between 4 levels of brightness and when I do it, the intensity of the backlight does not change (observed by peeking at the back of the screen module).Interestinglythe data sheet of the NL3224AC35-01indicates that there is a dedicated facility: "Luminance control" to change the brightness talking directly to the inverter but it seems that Anritsu decided not to use it.History:- The original screen had the tube deadand I bought a couple of new tubes.- After replacing the tube I discovered that there is something broken with the electronics of the original screen (it displays some sort of random dark digital noise).- I boughta supposedly tested screenbut it came with also the tube dead.- I moved the working tube to the Aliexpress screen and I've got to the place you see on the picture: Its electronics and backlight work but it is very dark.So yeah I think that whatever is acting on the RGB analog signals to adjust the brightness is probably broken and I need to track it down...Any suggestion is welcome.Thanks!JuanEDIT: This is fixed now!Turns out that the dim display was also faulty.The issue was fixed by getting a working display in place.

author: jdomenech
author_rank: Newbie
timestamp: August 16, 2025, 09:43:49 pm
content: The more I look at it the more I think the service manual is misleading when it comes to place the RGB Brightness control at the A02 Front Board.This board definitely interfaces the NEC NL3224AC35-01 to the instrument backplane (see picture below) but it sounds weird that the brightness control comes all the way from the CPU board to executed at the Front Board. It makes more sense that all that happens at the CPU Board; which is the source of the video signal.Front BoardI think the best strategy if to find the RGB video path at theA03 CPU Boardand with a bit of luck understand how the RGB brightness works.The video seems to be created by anADV476KP35 Color Palette RAM-DACand from there it seems to go toCXA1645M RGB Encoder(image below). This is a bit of an assumption from my side because this is a multi-layer PCB difficult to track...The presence of this Composite Video encoder is interesting because the composite video output does not have any brightness issue therefore the problem has to be downstream from this component.The encoder bypasses the RGB signals via outputs pins 21,22,23and that could point to the next step of the video path.CPU Board video cornerOn the solder side of that corner things are not very clear... but it looks like C30,C31,C32 placed just under of the Encoder could have something to do with either the output of the input of the RGB signals (image below).Let's hope those capacitors have something to do with the output and I can track it...Thanks!Juan

author: jdomenech
author_rank: Newbie
timestamp: August 24, 2025, 03:14:30 pm
content: Scratch thatThe RGB level controls seem to happen in the A02 Front Boardas the manual suggests.I've traced the RGB source in the video corner of the CPU Board all the way to the backplane connector pins 14A,14B,14C (image below).Once at the Front Board, the RGB traces go through a group of capacitors and aNJM2283Video Switch. These switches (the IC has 3) seem to be controlled by a single pin coming from the main unit (image below).Things are confusing afterwards but in any case there is a clear exit of that area to the Molex connector (25,27,29) for the RGB signals on their way to the screen.I've been probing those pins and changing the brightness setting of the instrument at the same time. Long story short: I can see the voltages changing accordingly (example below).I'm not familiar with RGB analog levels butthe important bit is that they move up and down together with the settings adjustmentso perhaps the brightness control is fine and the issue with my screen is somewhere else. Back to square one...Thanks!Juan

author: jdomenech
author_rank: Newbie
timestamp: September 28, 2025, 09:03:56 pm
content: This is fixed now!Turns out that the screen that had a dim image was also faulty (nothing to do with the RGB control of the instrument).The solution was to buy another display (it also came with a broken backlight) and swapping the backlight.Well, this was fun and I've learned a couple of things like how hard is to find a working NEC NL3224AC35-01 displayThank you!Juan