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Just fried my fm transmitter


harrison0550
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:?
Yup I made a huge newbie mistake trying to get rid of a hum and some static in my fm02 transmitter by hooking up the power inputs backwards. Needless to say it didn't like that and said pop! So back to the drawing board I go lol. Is there anything retail I can pick up Friday that will work? I know I'm an idiot but it is what it is. Just gotta find a solution now.

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Thanks Bob, I'm gonna try and avoid ordering anything online if I can. I may try the Belkin tune cast mod since it looks like my local sears carries them in stock (says in stock online anyway). I'm gonna try and not freak out just yet. I'm not planning to light up until DEC 1st anyway.

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harrison0550 wrote:

Thanks Bob, I'm gonna try and avoid ordering anything online if I can. I may try the Belkin tune cast mod since it looks like my local sears carries them in stock (says in stock online anyway). I'm gonna try and not freak out just yet. I'm not planning to light up until DEC 1st anyway.

I just finished my Tunecast II mod tonight, how far do you plan on transmitting? I'm getting 40ft through a few walls in the house, doing final field test this weekend. (Show starts Monday) The Tunecast that I got online didn't come with any kind of DC power, luckily I found a power supply in the junk drawer. I'm planning on sealing it inside a cup, and having it outside the door for max range. Looks like the cheapest/ most local option to me. Good Luck. :P
http://www.instructables.com/id/Belkin-Tunecast-II-FM-Transmitter-Mod/
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harrison0550 wrote:

:?
Yup I made a huge newbie mistake trying to get rid of a hum and some static in my fm02 transmitter by hooking up the power inputs backwards. Needless to say it didn't like that and said pop! So back to the drawing board I go lol. Is there anything retail I can pick up Friday that will work? I know I'm an idiot but it is what it is. Just gotta find a solution now.



Actually you may not have actually fried your transmitter at all just a/or components along the power trace of the circuit board.

Look at the power line tracess going into the transmitter, follow them and see if you find a capacitor along the lines, usually an electrolytic, they detest having voltages reversed and it may looked bloated, bowed, or even split or burst open at the top of the can (electrolytic capacitor), if you can still read the value on it, providing it is what is damaged, replace it. But before re-applying power, trace the voltage lines and look at other parts that may be close to and probably connected to the voltage input lines on the circuit board. You may have also fried a resistor or a transistor, if it popped, look for black scorch marks around the parts along the voltage traces that feed those components, if burned, broken or split and you can still make out the color code or the writing (numbers stamped) on them, replace any defective components you find.

Most often Radio Shack may have the parts locally and you could get new parts, replace them, and try again. Sometimes though you can't tell if a component has been damaged, but if you heard a pop, I'm almost certain its going to be a capacitor along the voltage supply lines, and like said earlier, chances are an electrolytic type.



Good Luck!
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I was actually just laying here in bed thinking the same thing Orville. To the point that I got up and looked at it out of curiosity. There are no burn marks or busted anything. However there are 3 capacitors in a row along the power trail. All 3 read "100 16V RVT". None appear to be busted or swollen but the first one in line seems to be sitting maybe a 1/16 or 1/8 inch higher than the other 2. You think that may be the culprit?

It is one like the image below........
imagegly.jpg
By harrison0550 at 2011-11-24

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Can you send a pic of the board? and yes, it looks to be a readily available electrolytic.

Good catch Orville.

A common method of avoiding this (in better units..) is to make them polarity proof..sometimes as simple as a silicon diode in line with the positive supply line. But when you make them cheap, corners get cut.

Another way to avoid it the next time is to make yourself a power cord, with a connector that will only work one way, one end attached to the power supply leads, one to the transmitter...so when you connect and reconnect power, you can only do it one way.

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Thanks Don. A Silicon Diode is the easiest route to prevent that I agree, but I do it in the following manner, just works for me. :(

And yes, that could be the culprit. Sometimes the BOTTOM of the can splits when these pop, so you can't always see it from the top, but if you have a raised cap that wasn't that way before, chances are THAT IS the culprit.

Some added information:

What I do to DC powered items that require an adapter is I will actually install a full wave diode bridge(referred to as FWB later in the post) across the DC input lines. Most can be bought for less than a few bucks at Radio Shack and they have saved me a lot of grief on DC powered items.

This acts as a WRONG WAY battery(incorrect polarity) protector, you wire the + and - from the adapter jack on the circuit board to the FWB ~AC~ inputs and then wire the FWB + to the + side of the + pwr input trace of the circuit board, - to - side of the - trace on the circuit board. Then it doesn't matter which way the adapter may get plugged in, it will always send out the correct polarity to the unit. BTW: this also converts ~AC~ to DC, so even if you plugged in a 12VAC adapter and the board required only 12VDC, that is what the FWB would put out in the way it is used here.

NOTE & WARNING: Any adapter above the voltage rating of the board will put that much voltage back out in DC to the board. If you fed it 120VAC you'd get 120VDC output, 24VAC would output 24VDC, even a DC voltage input would be the same DC voltage output!

And why I added the following information about adding a Voltage Regulator below.

You could go a step further and add a Voltage Regulator (referred to as VR later) that matches the units power requirement, 5vdc, 9vdc, 12vdc after the FWB to make sure it only sees that voltage and not over the voltage rating of the board.

Which I will often add this in the mix, that way if I have a unit that is say 12vdc and I accidentally plug in a 24VAC adapter, using a 12VDC VR would prevent nothing more than 12vdc getting to the unit.

This works really well with those adapters that have the interchangable tips that can be put in backwards and cause some mishaps.

These are just some of the modifications I will make to DC operated items that don't have a specific power brick with a cord that can only go in one way. But use a standard Wall-Wart adapter to supply power via a small jack.

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Make sure you are not missing a "fried" reverse polarity diode. Many units have those installed across the power input leads, to protect the rest of the components in the event of reverse polarity.

Those diodes are small, and easily "fried". They are cheap, easy to replace, and those you can get at R Shack.

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