Need help repairing a small flat CRT. - Page 1
Forum section: electronics / repair

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: July 27, 2020, 02:36:42 pm
content: Greetings,Recently I came across one of those camera doorbell thingies. It's a SAMSUNG SAV-410Y to be exact. They have a really neat monochrome flat CRT inside that is usually 12V and require only a PAL or NTSC input to work. So I decided to do a retro like project with that. I created the video signal with a STM32F1 and everything was working as intended.At some point all of a sudden the screen decided to move down by about a third of the way. I suspected some kind of DC voltage leaking into the deflection coils so I checked for bad capacitors. I saw two tantalum ones and since I've heard that those can go bad, I replaced them with anything I had available of the same values.And that fixed it... but only for a few days...Today I got a different problem. The screen was all shaky on the vertical axis and horizontal lines would appear. And to add insult to injury, the vertical screen shift from above joined the party as well...I swapped capacitors again but that didn't do it. The problem must be somewhere else. I gave the board a cleaning with some 99.5% IPA and the problem momentarily got fixed.After that, I sprayed some contact cleaner on the on-board pots and that seemed like it did something. But in the long run it didn't.https://youtu.be/hUgDQ6k_xHsAlso, If I touch a specific capacitor the screen does some funky business. Maybe this is a clue?https://youtu.be/aSEJU8x5mDwThere are a few test points on the PCB but without a schematic and some reference graphs I would just be wasting time.Also I noticed that the power transistors get hot fast! I know this screen is meant to be used for short periods of time but DAMN! Maybe they are the cause? But they were getting hot even when the display was running just fine. And the current draw isn't that bad. About 400-500mA at 12V. I know the cover says 16V but I'm afraid to push the screen any higher than 12V. It starts making sounds it shouldn't.I'd really like someone's help here. I have no idea the complex signals and voltages that those screen use so I don't think I can make it on my own.And I really want to use this gorgeous piece of art of a retro style project.Thank you all in advance,E.P.

author: fzabkar
author_rank: Super Contributor
timestamp: July 27, 2020, 07:36:31 pm
content: Start by identifying U101 and the 3 large 3-pin semis and the smaller 3-pin semi. The application circuit for U101 will probably reflect the bulk of the circuit.I always reflow the solder joints at the inductors and transformers, as well as any components which are subject to heating. I also go over all the electros with an ESR meter.I wonder if any of the trimmers are dirty.Edit:Here is a circuit diagram:https://elektrotanya.com/samsung_sav-410y_kaputelefon_sch.jpg/download.html#dl

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: July 29, 2020, 02:00:08 pm
content: Quote from: fzabkar on July 27, 2020, 07:36:31 pmOk so I took a look at the U101 data sheet but I couldn't get any help from that, It does have some input type signals but they differ in real life and the schematic does too :/I reflowed some suspicious solder joints but that didn't do anything. Cleaned all the trimmers, nothing. I even replaced the power transistors and mounted them on a heat sink.I didn't have the time to check all the caps. I only have one of those cheap component testers and I doubt that I can use that directly on the PCB without desoldering the caps..