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oxxyfx

Airwave 625 receiver issues

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Hi,

not too long ago I purchase 3 of the receivers in the subject line. Up till now I worked with the 623's but those are discontinued.

I soldered the receiver in my circuit - and supprize - it doesn't work. I mean it works - for 8 secconds then 8 seconds off. Then it comes on again, and 8 seconds later the picture disappears.

I thought this is a bad receiver. So I took the second one - doing the same thing... So I try the third one - this is the same as well...

This circuit is a new design, the receiver is soldered into it's own pcb with a connector which plugs into the baseboard. the baseboard contains the power regulator, the dip switch, the connectors, etc.

The only thing I did differently compared to the circuit I used the 623's in, that I added the reccomanded capacitors on the Video and the two audio outputs. My previous receivers didn't have that.

The regulator has 2 capacitors SMT 0.01 and 0.22uf.

All the traces are correct, no short circuit - I am stunned, I though I first ask you guys before I send it back to the provider.

Has any of you seen similar issue?

Thanks,

Ox.

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The good news is that if all three are acting up the same way, then it is something in your installation.

What Vreg IC are you using?

What are the MEASURED input and output Vreg voltages during good/bad operation?

What size cap is on the video output and which side is its (+) connected to?

Please post clear close-up photos of your board(s).

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The Vreg ic is LDO 5V, I believe it is 2940. The input voltage on it is 11.8V - from a 3 cell Lipo. The output voltage is 5.0V sharp.

Video output has a 470uF cap, positive is toward the Airwave module, negative is toward the TV.

I touched the capacitor's lead with the RCA jack - in the mean time connecting the RCA's ground to the ground, it does the same thing.

Here are some pictures, when this was taken the vreg was not fixed yet and the 2smt's on the vreg's leads were not soldered - but all that is done now.

post-5-1181189209_thumb.jpg

Edited by oxxyfx

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Your boards look nice.

Three things pop out right away.

(1) The LM2940 is dissipating about 1.5 watts. To avoid thermal shutdown, it must be bolted to your PCB. It may require additional heat-sinking.

(2) The stability caps on the Vreg are too small (are any really installed?). For example, the .22uF on the output might not prevent oscillation, which will cause very strange results. Please check the LM2940T-5.0 data sheet.

(3) The DIP switch appears to be set to an illegal channel.

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I'm for the DIP switch problem. Some modules, if more than one channel is selected, will switch between all the selected channels every few seconds. On your photo there are 3 DIPs set to ON. I can't see easily how you wired them, but on the module you have 3 inputs, if all of them are open or high channel 4 is selected, and each of them will allow to select channels 1,2 and 3 when grounded, but only one at a time.

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I guess that's a normal behaviour. Take a look at this page:

http://rangevideo.com/index.php?main_page=...4&products_id=8

"...If more than one channel is selected (up to 8) the receiver will automatically flip between the selected channels in 4 second intervals..."

I don't know which receiver module they actually use in this device, but it sounds familiar to what you're experiencing.

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It was the dip switch problem. I hate these when they do not mark it clearly which way is on, which way is off... On this one there is a line and it says "Open"...

On the test board I do have the LM2940T bolted to the board, and the caps are installed on the bottom - on these pictures were not yet on. The LM2940 is barely heating up, so I don't think it will need a heat sink. I will run it for a longer period to see if there is any heat problem.

Thanks guys, I love this forum.

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That is good news. Don't forget to install the correct VReg cap values, even if you see no problem (the .01uF and .22uF are too small).

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Well, home made... This is the most I can do at home... I yet have to find some kind of production facility in Canada who will do these designs el cheapo.

I asked for a quote from 2 of these, and got prices like $500 for 10 boards...

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I yet have to find some kind of production facility in Canada who will do these designs el cheapo.

Here are two affordable Canadian PCB fab vendors:

www.apcircuits.com

www.epcircuits.uniserve.com

I used AP Circuits (years ago) and didn't have any problems with them. I have not used EP Circuits.

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Thanks, AP was one I caled for a quote for the baseboard on the picture. The price came to $336 CAD for 2 boards - then when I increased the quantity I've got 15 for the same 336...

They have a deal - US$60 for 2 boards - but this does not include soldermask, silkscreen, any of this... Still that seems like a lot to me.

If I make it at home, not counting my time - only the materials it comes out to less than $5 per board...

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