Faulty FM transmitter

scamper

Dedicated elf
Joined
Jan 5, 2014
Messages
1,092
Location
collie
I am posting this hoping for a hail Mary ::)
But I expect a bin job :'(
I purchased a cheap Chinese transmitter
http://www.aliexpress.com/item/Freeshipping-home-Digital-PLL-stereo-power-FM-transmitter-home-radio-station-ant-power/669283395.html
I tested it fine, then set up my display and got it all working, I even had my sign IMG_5296[1].jpg with LED modules and a 3 channel controller , but I digress.
After 3 days, I went and turned everything on for some more adjusting and turned on some tunes then the radio to listen, but alas, The transmitter was no longer working :eek:
I tried everything from computer outputs, new audio leads.
I moved the channel up the frequency range and found that if it was set at 108mhz (as high as it goes) I could get a garbled audio on the radio, so I assume that the transmitter is not locking on a frequency or something.
The question is, has anyone ever played with these things, and had any success with repairs etc.
Back in the old days, I would have looked for a xtal that may have drifted or dry jointed etc, but most of this is surface mount, so I am guessing I am stuffed! :-\
 

fasteddy

I have C.L.A.P
Global moderator
Joined
Apr 26, 2010
Messages
6,645
Location
Albion Park NSW
Have you checked that the power supply for the transmitter is not the issue as Ive had a power supply fail before for my transmitter
 

gerry

Senior elf
Joined
Dec 19, 2012
Messages
813
Location
Surrey Hills,Melbourne
Does the display come on and is it the transmission that is not working ?

Have you tried setting it to a working frequency ie where a commercial radio station transmits on (for a short time) and see if it blanks out that station broadcast ? ---careful here !!

have you tried both the jack inputs ie audio and microphone and different sources of audio music ?
 

bbayjohn

Senior elf
Joined
Mar 4, 2012
Messages
579
Location
Batemans Bay
Some other things worth checking if you have a poor signal strength. Some radio transmitters have a high and low output, Check that your unit is set to high.
When the signal is a low and scratchy does touching the aerial making the signal stronger, you may have a loose areal cord.
Electronic noise - is the unit or aerial too close to another powered wire. Is the transmitter plugged into the same power supply as something else. Even its own power cord can act like an aerial, a Ferrite choke can reduce the Hum.
http://www.jaycar.com.au/productView.asp?ID=LF1294&w=ferrite&form=KEYWORD
https://www.youtube.com/watch?v=BxtXtgKBQzQ
Are you able to replace the aerial with a larger one? I used an old marine radio aerial and mounted it outside. For the connection to the transmitter I tried a few different RF connectors types but found with the Rca plug was easier to solder to. Then connect it to a Crimpless BNC Plug to RG6 http://www.jaycar.com.au/productView.asp?ID=PP0675. Now my transmitter is as clear again as it was 3 years ago.
 
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