Mini teardown: 5" HD 800x480px Car LCD Monitor Screen

[kwallen]

This is one of those weird Chinese products that has no model number or official name, but is ubiquitous in almost all online stores in under one description or another. It's a small, 5" 16:9 display that takes two composite inputs and claims to run on 12v (the silkscreen mentions 24v as well though). The screen is a little washed out and the video quality isn't particularly stellar, though the blue tint is an artifact of my camera and not visible in person. The cost for the screen was $14 USD including shipping. It draws an observed maximum of 0.15A @ 12v (1.8W) which seems pretty reasonable.

Stock image:



Teardown:















I was worried that the panel might be glued in, but it is just held in place with four screws and washers. The panel itself is extremely thin, so is perfect for integrating anywhere the composite video (or S-Video with a a hopefully small mod, the processor supports it but it's not broken out on the board) might be tolerated.

AMT630 - Clone of a MST703 "Small Size LCD TV Processor"
25X20BLNIG - SPI Flash
A5269 - 2A, 28V, 340KHz Synchronous Rectified Step-Down Converter
LPS F3T4 - Buck regulator for the backlight? Can't find anything on it.

[SeanB]

Funny enough I have one in the post on it's way to me. Going to be a replacement for a JVC portable television I use as a monitor. It will be a lot easier to carry up to the roof when checking satellite antenna alignment and changing LNB's. Monitor, decoder, remote and a 12V SLA battery means no mains lead needed unless I want to use the drill.

[jmag999]

Where did you find it for $14?

[kwallen]

Where did you find it for $14?

This particular one was from eBay, but I they're on Aliexpress and Banggood too for quite a wide variety of prices.

[princemoonrise]

Thanks for the pictures and teardown, it gives me a comparison to a couple of similar units I've been tinkering with.  One of them is a Taotronics I got off ebay for $18 since (the seller was in the same city as I live = faster than china), and the other is a generic security camera tester.  The Taotronics uses the AMT630, and the generic security tester uses the MST703-LF.

I noticed you mentioned that the screen may be capable of S-Video.  Oddly, I was trying to modify the generic screen to do exactly that, but was unsuccessful.  I looked at the pinout for the MST703 and saw on the diagram what should have been a C line and a Y line on the chip, and soldered a wire to that and to where the existing post-filtered composite video line went (same as the C line on the chip's pinout) but it didn't seem to work.

I was wondering if you had any suggestions or theories on how I could go about doing the mod, or if how I did it was outright wrong?  Attached is a pic of the before and after of my attempt.  The complete documentation for the 703 is at: http://wenku.baidu.com/view/53b8701ca8114431b90dd8be.html

I noticed in the programming manual part there were a whole lot of settings for video input types, but it seemed they usually grouped composite and s-video into the same so I would guess it should autodetect - but when I touch wires to pin 19, there was no difference or reaction in the signal.  I assume I'll have to run some resistors or capacitors for a "good" signal, but I would have thought it would have done something if I were on the right track.

Any advice would be greatly appreciated!

[bktemp]

S-video support has to be enabled in firmware. Autodetect is unlikely. Most monitors use buttons for input switching. If there is only one input this features is probably not used in firmware and the input is fixed to composite.

[princemoonrise]

I thought that might be a possibility as well, the complete docs actually say what the proper values for those settings are, though many of them default to auto.  I don't have the equipment or experience to try and reprogram the chip either.  I looked all over online for a 3.5" LCD with the S-Video connector onboard and the only ones I found are avaition/professional ones and they're in the $200-300 range.

[kwallen]

I looked all over online for a 3.5" LCD with the S-Video connector onboard and the only ones I found are avaition/professional ones and they're in the $200-300 range.

The configuration for my particular decoder is on the SPI flash, but I couldn't find a datasheet on what the configuration looks like.

The Playstation One had a nice little add-on 5" LCD which takes both composite and s-video, they're often dirt cheap on eBay and very easy to modify.

http://kyorune.com/modding/article.php?id=52

Would this suit?

[princemoonrise]

Thanks for the suggestion!  I do have one of those PSone screens from back in the day, though its being kept with a friend at the moment.  I think the power draw and tech from these car backup type screens is likely better, though.

Noticed your link went to a Sega related display hack. Coincidentally my original intent was to use the S-video mod output to the screen to revive a Sega Nomad with a dead screen, but that limits my options to a 3.5" size.  I've since just settled on composite since it seems to be good enough at that size, though it would be nice to know if its possible to hack any of these inexpensive car backup screens to s-video capability for future projects.

One other thing I was wondering if you might have any insight into pertaining to these car-backup lcd monitors, is why some models have a major problem with the video signals displayed by the Sega Genesis game system in particular. The Taotronics Car Back-up screen with the AMT630 chip has this problem. If I plug it in, it will display in black and white, if at all, and drop out erratically. Other game systems and video equipment display on it fine, just not the Genesis.  The MST703 unit I have has no such problem, and will display the Genesis video signal properly.  From what I've seen looking around on the net it seems like newer versions of the car backup screens use either a different chip or firmware setting, and a much smaller percentage of the screens work with the Genesis video signal now than those manufactured just a couple years ago.  Some people think it could be because the Genesis does not output a standard NTSC number of lines.  I think it could be either the chip used, the firmware settings or the panel itself.  Since it seems like you know a bit about these I was wondering if I could get a second opinion or insight into this problem.

[bktemp]

The auto format detection typically looks for the color carrier and the number of lines. The ICs I have seen are dumb. For example for  the VGA input there is a huge table programmed into the firmware with horizontal and vertical frequencies and the resulting timings. Every resolution the monitor supports, must be programmed into this table. If you input a resolution that is not in the table, the monitor either does not work at all, or it chooses the nearest timing, but this does not really match. The same applies to composite/s-video inputs. All supported modes must have been programmed into the firmware. If the resolution does not match, the firmware does not know how to set the buildin scaler to adjust the video resolution to the screen.

The older small screen lcd monitors do not have any firmware at all. They use asics whis hard coded scaling settings (often simple line dropping) for NTSC or PAL. Some support both NTSC and PAL, but most of them are fixed to one timing. They typically accept a wider variation of the timing because they do not detect and switch to a wrong format if the timing is off.

[magisterek]

I just wonder if it would be possible to bypass this A5269 buck converter and supply the bord with low voltage directly. I can see in datasheets that MCU and  flash memory need no more than 3.3V but I am not sure about the backlight. It would be nice to power it with single Li-po cell and use it fore examle in FPV googles. Does anyone have any idea if it could work dierctly at 3.3 to 4.2V ?

[krivx]

Does anyone know of a similar LCD that supports an RGB input?

[NiHaoMike]

Many of the smaller LCD panels accept RGB.

[richms]

Ive got a similar screen that came with a wireless reversing camera kit. Im about to open it up to see if I can jam the receiver for the wireless link into the shell of the camera since its a mess of wires with it separate.