Disassembling LK-7900


Mar 31, 2013
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United Kingdom

Since my LK7900 is pretty much useless with its bad focus, I thought I would see if I could fix it.

Taking the cam apart is very easy, once the magic incantation is known!

I am not going to post the method, until I am confident that it will work again after reassembly.

I wish I had thought to take some pics, before I did it.


1. Your cam will not be as pretty after you take it apart, as the flashy bezel gets grunged a bit!

2. I do not know whether, once I put it together again, whether it will work!

3. I cannot think of a way of testing the focus, other than painful reiteration of dissemble, adjust, reassemble, test, repeat adinfinitum.

The lens is adjustable on a screw thread UNFORTUNATELY it is glued into place with (I think) varnish.

I have scraped off the visible glue, in the angle between the lens and screw housing, however I cannot rotate it, it must have varnish down between the threads.

It is not the sort of item one can take a pipe wrench to, to unscrew it!!!

I have attached a couple of pictures of the lens unit.lens1.JPG lens2.JPG
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I guess to focus it you will have to power it up while opned and then have a TV connected to the AV out port.

Is it possible to detach the image chip Circuit bord from the lens socket ? if it is you could try to use some solvent to make the varnish/glue go soft.
You might allso be able to make the glue go soft by applying some heat to the assembly. a heat gun or maybe a Little propane torch or lighter at a distance. ( it should not be nerrerseary to make the thing red hot )

I think the lens itself should be pretty durable as its made of metal, the socket the lens screw into might be plastic tho i have allso seen them in metal on some CCTV cams.
But it is proberly only poor grade ALU or simmilar so you might crush the socket and or lens if you go Gorilla on it with the pipe wrench .

The lens Mount used in your Lk7900 dont seem to be exaktely as the MTV mounts used in CCTV cams, but one of those might be useable none the less if the original one fail during dissasembly
In this video you can see them adjust the focus ( on the image part itself not a assembled camera )
If Lucas do it the same way i know what have gone wrong, your camera lens have proberly been touched a Little between focus adjust and lens fixation ( glue )
I know from the CCTV cameras it only take a Little turn of the lens and it is out of focus.

From what i can see on the video it is a thin liquid varnish / glue witch is used, it shouldent sink too far into the tread of the lens and Mount so it should be possibel to pry the Things apart. ( i dont think they use CA glue as that to mee seem like overkill )

Focus @ 10:50 and lens fixation @ 12:10

Need more info - my 7500 is useless because of poor focus as well, and my next step is, like yours, disassembly. I sent video to Lukas showing that a splattered bug on the windshield 1" from the lens is in perfect focus, but you can't read a license plate on the car ahead of you at a stop light. Obviously mis-focused, but try convincing Lukas of that. Thanks for your help, try to fill in the blanks of your disassembly process if you can.

John F
Damm :oops: if you have a video with the cam focused perfektly on a bug 1" avay, that should indicate a clear focus error from the factory.

I would say these cams need to be in focus at 2 M, longer than that will be rendered mute by the wideness of the lenses.

Im sorry i dont can afford to ( maybe ) kill my camera, otherwise i would have pulled it apart and made a guide on getting the lens Loose and how to focus it proberly.
But sadly i am without a job and can not afford to by a new cam if i broke it. :(

Hope you Guys get up and running and in focus soon, aside from the problems you have encountered these Lukas cams seem good.
Hi All,

Some progress!

I scraped all the glue out of the 90 deg recess between the lens and the holder with a fine needle.

I then wrapped the lens holder in tape and with a VERY small pipe wrench, gripped the lens holder front section through the tape. I held the lens holder body with just finger grip in other hand, gave a turn anti clock and the glue gave up.

I can now screw the lens in and out reasonably easily. Left the lens in place to protect the ccd and the IR filter, and generally keep sh1t out of the optics.

Next job is to wire up a mains to 12v power supply with a 3.5mm jack on it and power the camera on my work bench.

The way the camera is designed, means that it has to be reassembled to test it, unfortunately the lens and ccd assbly is first, then the huge heat sink, which is taped to the CCD sensor, then two pcbs, screwed together. There are push fit connectors between each assbly, that have to be aligned properly, otherwise kaput camera! Once the cam is assembled, the only part of the lens you can get to is the flat annular end you can all see at the front.

I may be able to reassemble the camera and then turn the lens holder by applying frictional turning force on the front, (use an erasor or similar). If I can do that I can fix the lens position with a drop of adhesive between the hole in the camera front body and the lens holder.

I do not want to keep taking it apart as I am sure as eggs are eggs I am going to bust the connectors before I finish!

I strongly advise everyone NOT TO TRY THIS AT HOME YET!

Let me do some experimenting and find the safest way to do this. If I can do it, I will write it up for you.

Be aware I have been using a x50 binocular microscope that I use for surface mount work. You will need fine tools and some form of magnifying aid. This stuff is delicate!



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Attached is a bmp of an old (1973) numberplate I had kept in my garage as a momento (it was a donor car I made into a kit car Eagle Jeep with my son).

This was taken at about 6 yards distance. its 100% better than before!

Adjusting the focus is very easy, I reassembled the camera loose, i.e. no screws, without the front half shell, allowing me to turn the lens focus screw at will. You have to be careful handling it in case it all falls apart !!!

The settings of the camera are also important, I need to vary sharpnes, video quality, noise filter and see which is best.

It is only ONE HALF A TURN from blur - sharp - blur

I will try it at greater distances this afternoon. (limited by the mains power supply).

I will document it and post in a day or so.


Nice presentation and a lot of work, it wont hurt for you to send your results to Lukas they might impliment tighter controls at the focusing stage of assembly. I am sure that they would wish to present a finished product that is nothing less than perfect.....That said I wonder how many people finished up with a DAGENHAM DUSTBIN thats a ford car that came off of the assembly line finished in a hurry on a friday afternoon so as not to intrude into the assembly workers weekend......( the explication is for the un-initiated) .............Ipol o_O
I have a cousin who worked on the Fords of Dagenham assembly line and he related the friday afternoon scenario to me.....any ford owners out there .......my commiserations......:D ( I am joking I am joking ) its the english sense of humour kicking in again.....what do you expect on a cold and miserable sunday afternoon.....Regards to all you DCT folks .....Ipol

Well I have done a lot of experiments, but I am not convinced that I have improved the distant focus.

To understand this you have to remember your old photographic skills, before there were auto focus point'n'shoot cameras.

Have a read of this:- http://en.wikipedia.org/wiki/Hyperfocal_distance and also this ;- http://www.videosec.com/education/lens-glossary.pdf

In optics and photography, hyperfocal distance is a distance beyond which all objects can be brought into an "acceptable" focus. There are two commonly used definitions of hyperfocal distance, leading to values that differ only slightly:

Definition 1: The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.

Definition 2: The hyperfocal distance is the distance beyond which all objects are acceptably sharp, for a lens focused at infinity.

The distinction between the two meanings is rarely made, since they have almost identical values. The value computed according to the first definition exceeds that from the second by just one focal length.

As the hyperfocal distance is the focus distance giving the maximum depth of field, it is the most desirable distance to set the focus of a fixed-focus camera

My problem is trying to find and set the focus at the hyperfocal distance.

The focus adjustment is about a half turn on the lens. The VGA output of the LK-7900 is bloody useless at fine comparisons. On my 1600 x 1200 monitor, the image at vga resolution is crawling with aliasing pixels. The only way to see an improvement is to take a video and look at it with the Lukas viewer. ( and of course there is a mis-match between the Lukas viewer and the monitor, which again introduces crawlies.

SO I have set the focus to be the best I can obtain, I have reassembled the camera ( IT STILL WORKS !!!!) and will try it in the car again.

I will wrtte a note on how to take it apart later. I have taken some piccies.



READ THE WHOLE PROCEDURE BEFORE YOU START. If you do not feel confident that you understand and can perform the procedure then do not start it.

Before you start ---- I will not accept responsibility if you break your LK-7900, you do this at your own risk! I repeat, if you try this you are doing it at your own risk... Dash cam talk forum and I are NOT liable if your LK-7900 does not work after you attempt this!

ALSO before you start to disassemble, check the camera works with your bench 12v supply and VGA connected to a monitor.. Lets start with a known working item!

1. Remove SD card and all cabling.

2. Put camera on work bench lens uppermost. mount block (GPS) at 12 oclock.

3. At six oclock (bottom ) find small 2mm notch in rim ( pic 1)
Insert a small thin flat blade into the slot and carefully start to lift the label upwards. Great care should be taken not to crease the thin plate.
Gradually work your way around the whole ring until it comes free. Lift it away and store. The reverse side is tacky with impact adhesive.

4. You will now see two holes at the bottom of the cam, previously covered by the plate. (pic 2)
5. With a small x-point screwdriver remove the two screws. With the cam lens upwards, lift the front plastic housing (containing the lens turret) away from the rear housing.
Do this gently and keep the lift straight. The only thing holding the two halves together are the plugs and sockets on the pcbs. When you split the housing, either the lens pcb or the larger circular pcb will come away from the rear pcb which is screwed in. (pic 3) The lens holder and ccd pcb is screwed to the inside of the lens turret.
6. Carefully remove the square of glass tape that is stuck onto the lens holder and heat sink.... You WILL need to use this again so remove it very carefully! pic 4 and pic 5
pic4.JPG pic5.JPG
Put a mark on the heatsink and edge of pcb so as to know orientation when reassembling cam.
Unscrew the two x-point screws and very carefully lift the lens holder up and away from the heat sink.
There is NO need to remove the heat sink from the front housing.
7. With a fine pointed needle remove the glue between the lens holder and lens holder body, and free the holder so it can screw in and out freely. I had to wrap the lens holder in insulation tape and use a very small pipe wrench to break the stiction of the glue. Be VERY careful!! The HD cmos sensor is inside the assembly. Do not use solvents or heat to free the thread YOU WILL DESTROY THE CMOS SENSOR IF YOU DO.

IMPORTANT --- Do not remove the lens holder completely from the housing. It is keeping the cmos sensor from being ruined by dust and foreign matter falling onto it.

8. When the lens holder is rotates freely , then reassemble enough of the camera to test it. (pic6)

Temporary reassembly,

8.1 Gently press the loose circular pcb onto the fixed pcb, ( that is screwed to the rear housing), making sure the two mating halves of the inter pcb connector engage.
8.2 Gently press the lens holder sub assembly onto the circular pcb, making sure that the pcb connector is oriented the RIGHT WAY ROUND.
8.3 Be careful if you tilt the cam forward, the pcbs will fall off. Secure the pcbs with a strapping of insulation tape for safety.
8.4 Connect the VGA cable and the 12v supply. Insert your sd card into the camera. Do this gently otherwise you will push the pcbs off each other.

9.0 Now the acid test! Switch on and you should boot up and get a picture.

10.0 Set the focus to your hearts desire. Just gently screw the lens in and out until you get the sharpest focus at the distance you want the sharpest focus to be at.
Its very sensitive, about one half a turn to go from blurred to sharp to blurred again..
I used a camera target downloaded from the internet (pic 7)

10.1 When you have finished adjustments and tests, put a drop of glue on the lens thread and leave to dry.

11.0 Reassemble (the reverse of above.)
11 .1 Tear down test assembly
11.2 Put lens holder back in front housing IMPORTANT MAKE SURE IT IS THE CORRECT WAY ROUND SO THE TWO HALVES OF THE PCB CONNECTOR WILL MATE. If you marked it before disassembly it will be easier to replace correctly.
11.3 Screw in two screws to hold it in place.
11.5 Replace the round pcb onto the fixed round pcb.
11.6 Carefully offer the front housing to the rear housing ensuring the lens pcb connector mates correctly with the front round pcb connector.
11.7 Replace the two screws through the holes in the front housing
11.8 BEFORE replacing bezel on the front...... Apply power and TEST it is all connected and working correctly. ( The first time I got to here it failed because I had a strand of cloth across the ccd connector.)
11.9 Put the circular bezel in correct position and smooth down into place.



You are a hero for taking this on. When I've had enough to drink to I'll update differences I find doing it to the 7500. Here is a screenshot showing the white bug splatter lower / middle in focus, hood reflections in focus, anything further poorly focused. Bug splatter was less than 2 inches from the lens.
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Oh, do your test focusing in low light, as that gives you the smallest 'depth of field' therefore most precise focus distance. I'll shoot for best low light focus at 10 feet - in good light I'll expect good focus from 5 feet to infinity.
I sent a requested dropbox link to video clearly showing the issue to the Qrontech person I had been dealing with, and the email was rejected because of a full mailbox. Not a good sign. In the mean time my $52 G1W is doing a fine job! I love the features of the Lukas, and know that the video quality would be excellent if it was properly focused. Looks like factory support is a bit shaky though. In all fairness, I bought it off fleabay and the seller cannot help. It did appear to be new, factory sealed.
@ johnf try this email address kjmj0807@naver.com Its another Lukas email address .......I think the 0807 are all numbers best of luck Ipol
Thanks Ipol, I sent an email, will let you know if I hear anything back.
Beautiful! Splendid work. Thanks for the write up.
Thanks for this. Tell us if you managed to focus it properly. Unfortunately, it's difficult to achieve acceptable sharpness using hyperfocal distance without indicators on the lens, just like on vintage camera lenses. Hopefully, I won't have to do this in the future.
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Lot of thanks for this work .
I did the same but on a cheap dash cam ....less stressfull for sure.