4.3-inch monitors and a bit of DIY tinkering.

At one of the sites I look after, there are around 12 video intercoms. I bought some of them myself, mostly the well-known Commax models, but there are also some less familiar Kenwei units, which, like the Guardis, are copied from Commax. They’re usually copied almost down to the last detail, but as always, the devil is in the details.
Commax monitors are pretty good, and I try to use them whenever I can. But some of the monitors were already Kenwei models, and people had got used to them. When the first few monitors went dark, I replaced them with the same models. Kenwei has one feature: you can open the door without picking up the handset, which people found convenient. I could have bought a Commax and modified it, but that would have voided the warranty, so I didn’t. Commax monitors do have better-quality CRTs, though, and they last longer.
Since the monitors aren’t installed in homes and are switched on more than 50–100 times a day, the CRTs in the Kenwei units start to fail after about a year and a half to two years. Replacing the monitors again would have been pretty expensive, so I decided to convert some of them to LCD screens.
After talking to my friend lolipop, I got the panel dimensions (many thanks to him for that). There was 108 mm of space for the installation, and the panels in the monitors I’m reviewing measured 105 mm. It was a very tight fit, but I decided to take a chance.
I ordered five right away (it was a little cheaper that way) and waited.
They arrived in about three weeks, with tracking. Just a couple of days ago, I picked up a fairly large package from the post office.
Inside were five identical little boxes. The packaging was a bit flimsy, but everything arrived safe and sound.


Each little box contained the monitor itself, packed in a resealable bag, a power cable, and an instruction manual. A modest little bundle. The box is fairly large and sturdy; with a bit of effort, they could have fit a couple of monitors in there.


There was nothing particularly interesting in the manual.
It lists the technical specifications and the wiring diagram.
The monitors have a resolution of 480x272 and a 16:9 aspect ratio. A 4:3 model would have been much more convenient for me, of course, but I couldn’t find any suitable ones. More on that later.


The monitors themselves look quite neat. There are no labels or markings, not even on the control buttons.


I decided to take a group photo here. Buy four more monitors and I could make a little video wall :)


The manual lists power consumption as 3 W, but in reality it’s 1.5 times lower. By the way, power consumption doesn’t depend on screen brightness, which suggests that the backlight always runs at a constant power level.


In standby, the monitor uses even less power—just 0.6 W. Though in my opinion, that’s still quite a lot for standby mode.


There’s almost nothing inside. Just the panel in a sheet-metal housing and a small board about the size of a matchbox. The processor is an AMT630, a chip that integrates all the circuitry needed for video processing and panel control. The only external components are an EEPROM and two PWM power controllers. As far as I can tell, one powers the processor itself and the other powers the backlight. The main PWM controller is an XL1509. There’s also a board with the buttons inside. The connection uses two wires; each button connects them through a specific resistor: 1–2–4.7 kΩ.


The monitor housing measures 122x72x15 mm, excluding the stand.
The LCD panel itself is naturally a little smaller. Datasheet for the panel.
Length: 105 mm


Width: 68 mm


Less than 3 mm thick; the panel is very thin (and that's including the metal frame.


I originally planned to include photos of the screen from different angles, but I couldn't get any decent shots (I can add them if they're really needed), so I'll just describe it.
The picture is best when viewed from the front. From above, the left, or the right, it's a little washed out, but still acceptable. The worst part for me was that the picture gets darker when viewed from below, and I need to look at it from below (because of how certain video intercoms are installed). A shame.
Overall, the picture is sharp, but I wouldn't say it's very bright. I wish it were brighter.

That brings me to modifying Kenwei video intercoms. I think this modification should also work with Commax and Guard models (and many similar ones), since they're all practically identical, and often even use the same wire colors.
The originals that all these copies were based on were the very common Commax DPV-4hp and Commax DPV-4MT. Their successful design led to them being copied by just about everyone. Many readers have probably seen monitors like these (and their upgraded versions) in apartments and offices. I'll be modifying a model copied from the Commax DPV-4hp.


In short, I think the modification was a success. My only complaint is that the new screen isn't very bright; I expected more. But I hope this setup will be more reliable than the old CRT.


Summary.
Pros —
All 5 monitors work.
Excellent image quality; I didn't even spot any dead pixels.
The screens from these monitors are well suited to modifying video intercoms.
The price is quite reasonable.

Cons.
In my opinion, it could be a bit brighter, though maybe I'm just being picky.

I hope you found my review useful. Leave your suggestions, questions, and comments below.