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May 01, 2013, 09:41 AM
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Mini-HowTo

Repair a fried minimOSD (max7456 chip)


As many people, I fried two minimOSD [switching regulator version] ... This is the faulty setup:

- 3S lipo connected to an ESC with BEC. The 5v output powers my flight controller (CRIUS AIOP) and the digital side of the minim OSD.
- The video power of the minim OSD was connected directly to the 3S Lipo (~12v).
- This worked for some time, but then, the MAX7456 chip died during tests (Atmet chip still ok, but no video output).
- The cause is still not completely clear to me... However, the Maxim data sheet says that there should be not more than 0.3v difference between the digital and analog grounds. Since I used a single battery, the two grounds are connected (via the lipo, the ESC and the CRIUS board) but when you plug/unplug it could be that there is a transient voltage difference exceeding 0.3v ?

- Anyway, you can ask for some free 'sample' MAX7456 chip on Maxim's web site (for test/evaluation purposes) to repair a fried OSD .
This is how I did it:

0) Check that the Atmel chip is ok by connecting your (dead) minimOSD board to the configuration software.
1) Remove the Max7456 chip, cutting the leads with some hobby knife (no special soldering tool needed).
2) With a small iron tip, remove the small pieces of leads left on the board. Check that you did not shortcut two neighboring pads.
3) Solder the new chip - a magnifying glass helps. This is the slightly delicate step if you are not too familiar with soldering. I did it without flux, but it is probably better to use some.
4) Check the OSD.... It should almost work, but the character set needs to be updated with the OSD config. software (and FTDI/USB adapter)

After that, I have connected the digital and video power rails directly on the minim board (some versions have solder pads for this). So there should be no ground voltage difference anymore and I hope that the max chip will survive longer ! Of course, the "12v" input on the video connector should not be used anymore.

I may get some parasites (coming from servos or the ESC) in the video output, but this can be cured with some appropriate LC filter (I do not want to use two separated LiPos in my plane).

EDIT: several flight with this setup now, and no parasite all all ;-)
Last edited by grmis; Jun 17, 2013 at 05:46 AM. Reason: typos & english corrections
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May 01, 2013, 12:34 PM
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Great post. Thanks for the detailed rundown.
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May 01, 2013, 02:56 PM
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Thanks !
May 10, 2013, 04:41 AM
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Fried max chip


im struggeling to get the overlay working here.. it used to work but when i tried it today there was no overlay (not even the booting up part)

im getting video trough the board

Is the max chip fried then?
Will i loose the entire picture it its fried or just the overlay?
May 10, 2013, 10:22 AM
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Originally Posted by svefro View Post
... Will i loose the entire picture it its fried or just the overlay?
Good question... when I fried mine, I was doing some tests *without* any camera, so I can't tell you. One test is to try to connect to the software configuration tool to see if the Atmel chip is still alive. By the way, the two leds are "on" ? Did you change anything to the wiring since last time ?
May 10, 2013, 12:25 PM
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i have tried connecting the arducam config, i can download and upload configuration changes and flash firmware and charset without error messages.

i have power to the analog stage from a 3s lipo, the 2 red leds are on. i used to get the boot message or "waiting for mavlink data" on the overlay, but i dont get that anymore.. same wiring that last time there.

But i had a mishap when connecting it up again to ardupilot.. i had put the camera cable on the wrong way. (camera video out to ground and camera ground to video in). i really didn't think this would damage any thing else than the camera. but the camera is working fine.

The very first time i connected it to ardupilot it was working until i connected a ESC to the output rail, then the overlay disappeared. Removed one of the ground wires to minimOSD and it was working again with the ESC Connected.

I have a bad feeling that my max chip is fried since i don't even get the "Booting up" overlay.
May 10, 2013, 04:15 PM
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Quote:
Originally Posted by svefro View Post
i have tried connecting the arducam config, i can download and upload configuration changes and flash firmware and charset without error messages.
So at least the atmel chip is fine, good.
...
Quote:
Originally Posted by svefro View Post
I have a bad feeling that my max chip is fried since i don't even get the "Booting up" overlay.
I would bet that the video chip is dead indeed... This chip is quite sensitive to slight voltage mismatch between the digital and analog grounds. Connecting the analog ground to a video signal might have killed it ? You could order a few for free from Maxim's web site, doing the replacement is really not hard/long if you have a soldering iron with a small tip.
May 10, 2013, 05:29 PM
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That's what i was afraid off I have just placed an order on 2 samples. Do they do some kind of evaluation of the request?

I see Hobbyking have the MinimOSD v1.1 at 19$. i think ill order that one also just to be safe. Guess ill go for soldering the bridges so i don't fry the new board too. I don't want to use 2 lipo's either
May 11, 2013, 02:13 AM
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Quote:
Originally Posted by svefro View Post
... I have just placed an order on 2 samples. Do they do some kind of evaluation of the request?
I ordered my "samples" a bit more than one year ago (for a different project), and they never asked me anything since then.

Please tell us if the reparation works !
May 12, 2013, 11:24 AM
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Originally Posted by grmis View Post
Please tell us if the reparation works !
Will Do
May 29, 2013, 03:09 AM
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Quote:
Originally Posted by svefro View Post
Will Do
Got my samples.. Replaced the Chip but it didn't help.. maybe my soldering skills wasn't enough to get that small chip installed correctly. i just ended up with no picture at all but i'm still able to update the charset without error messages.

Anyways.. i've got a new board on the way in the mail. i think i'll just solder the bridge to the analog stage straight away. it's an easier hookup that way it seems. i just hope that i don't get a lot of noise on the video.

Thanks for the help
May 29, 2013, 03:19 AM
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Quote:
Originally Posted by svefro View Post
... Replaced the Chip but it didn't help..
Oh, I am sorry that it did not work for you. It may be that two pins were shorted ?
Or some bad contact ? Maybe you can check some on them with a multimeter ?

Anyway, in my case the image has no parasite at all (with digital & analog lines connected), even when the servos and/or motor are running.
Jun 07, 2013, 08:14 PM
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Does anyone know why the unit is 7-12V input only (Version with onboard switchmode powersupply)
The switchmode reg LM2842 (marking STVB) is rated to 42V input
http://www.ti.com/lit/ds/symlink/lm2842.pdf

The diode (marked S4 in SOD123) is i believe a SD103AW which is 40V
http://www.diodes.com/datasheets/ds11013.pdf
However it is a little hard to tell as the packaing info says S4 might be the CW version but even that is rated to 20V

All the caps involved and ceramic and likely 50V

In fact, does anyone know where the circuit diagram is, complete with the components used on it.
I've not found anything.
Jun 17, 2013, 05:03 AM
throw new IOPilotException();
IceWind's Avatar
Mine was working fine until it start to randomly starting to fail to start but I'd always have image from the camera. Than it start to get even more difficult to start like 1 in 10 times and sometimes all I got was a grey screen. After it would start but after 10 to 15s it would go out, the image from the camera was gone and I was left with a grey image.

To me this seems more like a problem with a leaking cap or any other part that is damaged, but I wasn't sure if this is the behaviour of a fault MAX7456.

When the MAX7456 dies, does it stops working completely and there is no image passthru from a camera or the behaviour is different?
Jun 17, 2013, 05:44 AM
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Hi. In my case, the video chip stoped working completely, so it looks different from your problem. I cannot say if the image would pass through a dead max7456 because I was doing some tests without any camera when this happened to me (two times).


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