Here is the problem I am having: I was only able to get the transmitter to function once (although it took about 20 seconds before the PLL would lock), but then the next time I turned it off and back on when I tried to use it again the PLL would no longer lock at all no matter what frequency I selected (it is supposed to display the word "lock" on the screen). Another thing I noticed was that the 78L05 transistor was REALLY WARM! I am still unable to get the PLL to lock after multiple tries, besides the first time I powered it up. I have a receiver within inches of the transmitter and I cannot pick up any signal.
Here is my diagnosis so far: RF output stage BD140 transistor tested good 2n3904 transistor next to PLL chip also tested good 78L05 chip was really warm. I get 4.89 volts on the VCC pin 14 of the TSA5511 The entire thing is drawing around 115mA at 13 volts when powered up. I have tried tapping on the circuit board in case something is loose however nothing changed. I have tried adjusting the RF output pot as well as the trimmer next to the 3.2 MHz crystal, but it still did not change anything.
What is the usual cause for a PLL not locking?
Does anyone have any experience with this transmitter?
Unfortunately it is too late to return to Ebay so I would like to fix this myself if I could.
Did you check the 7805 voltage pin output? If it's getting abnormally hot I wonder if it's slamming the other components with higher voltage and maybe your TSA5511 is dropping the voltage near where it would be otherwise. Not sure how it's designed though. Maybe check the unlocked frequency with a counter to see if it's close to where it should be to find a lock? The crystal on that board in the ebay pic looks like it has a variable capacitor next to it to adjust oscillation of the crystal (edit: oops just realized you already tried that) but if I were you I'd contact the manufacture and see if you can get a schematic or help. Best of luck.
Sounds like it may be a common problem or potential design flaw in the buffer transistor coupling to the IC? Bit tired right now but that's what I grasped from that.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~