Uniden Pro510XL Not Transmitting

I would not worry about the 5.6 ohm R49 is my first thought. But, there is a weird failure mode you only see once in several years, due to poor quality disc ceramic capacitors. As example once I had a Cobra with a channel selector miscounting. Turned out to be a dead shorted .01 uF disc, only logic levels in it so for a 50 volt disc you would never think it would short, yet the RF coupling disc from driver to final (C41 220 pF) sees higher peak voltages thus is much more likely to fail shorted than the one in my example. If this happened the rail from the driver collector would go through the 5.6 ohm to ground through both the final base-emitter junction and the 15 ohm base resistor R48 harming all three parts. A good eye helps here, if the 5.6 ohm does not look discolored I would not worry about it or the capacitor, considering in this case a bad antenna or defective final was the sole cause of my problems. Then I would only consider the final, 15 ohm resistor, Spik diode, transformer windings. Helps to have a meter to check the driver coupling capacitor for a short. Honestly if I had no way to test the cap and resistors I would replace them to avoid the off chance my new final will burn up for no reason.

The final could have failed from a bad antenna, defective manufacturing, or the driver coupling cap shorting. If you cannot test them your only talking under a quarter to replace the cap and both resistors so why not. All you know for sure is the final and the 15 ohm base resistor are bad. If the final shorted high current flow could short or open the Spik diode D7, and melt turns together in the audio transformer so long as D7 was not open circuit while the final was shorted. The transformer is easy to test by turning up the volume reasonably load in receive. If everyone sounds OK then you are good to go there since shorted turns in it would cause severe distortion in the RX audio. The Spik diode needs a meter to test but fixing the final problem and testing the radio also tests it for open, as the rail must be getting through it to power the final in TX. Meaning if it appears to key up and talk normally the Spik diode (a 1N4003 but I do not see why you could not get away with a 1N4001 here) is not open. This does not mean it is not shorted however. I cannot stress enough how important a decent DVM is for anyone repairing most anything. Not all these things I mention are your issues I am simply posting all of the things I would consider. Even if shorted I doubt you would notice it in the TX audio unless really driving the radio.

The thermal compound is not tan it should be very white and thick yet fluid, not a 'gum' at all! At least I have only used white compound but this does not prove other colors do not exist out there.

Heat sink grease : (which I call thermal compound as do many others)

http://www.radioshack.com/product/index.jsp?productId=2102858

Be very delicate with the old mica wafer, good to replace and radio shack carries them IIRC. Don't remember for sure, the one here closed 3 years ago so it has been long since I was in a store and they alter their product line often. Clean the wafer and back wall of old thermal compound and grit, applying a thin even coat to both sides of the wafer so contact from final to wafer and wafer to wall is good. Really I am giving you too much to worry about but I like to cover all possibilities.

 

Sounds to me like your in over your head with this. I never mentioned steel wool. I said a paper towel wet with alcohol such as rubbing alcohol. The surfaces must be clean. I think you should just replace the 15 ohm resistor and final and try it hoping you get lucky. After watching a few utube vids on replacing finals paying careful attention to how the hardware is assembled and not forgetting the shoulder sleeve washer on the screw.

 

direct short if the fuse is blowing right away

 

You either damaged the heatsinking hardware or installed it incorrectly and the collector of the final is touching the back wall directly shorting it to ground. This model is not chassis isolated. The final must be heat sinked but electrically isolated from the frame. You should stop powering it before you burn windings in the audio transformer and/or blow the Spik diode. Fix it. Try again. Start with a 1 or 2 amp fuse to be safe the first try.

 

And keep posting your results! This is a good thread!!! And thank you Mr. Outlaw for taking the time to hang in here with him!! Very cool!