replacing finals in grant xl

[BOOTY MONSTER]

ive picked up another uniden grant xl with the PB-208AC board . it was given to me by someone who i helped with their computer . i was told the finals were burnt out by high vswr . i hooked it up and it recieves just fine , but it doesnt transmit .

what do i need and how do i go about changing the finals ? im not concerned about using exact replacement parts and using mosfets will be just fine if their easier to get or cheaper . the few extra watts mosfet's might do doesnt matter to me because ive got a small 2 pill when i need the bump in power . i just want the easiest and cheapest way to do it ?

will the radio need to be realigned after the finals are fixed ? and will TIM for computer CPU's be ok to use for TIM on the radios finals ?

thanks

 

[Shockwave]

Before you change the finals you might want to check transistor number 41, the series pass modulator. If it's working you will see about 6 volts at test points 7 and 8 to ground when you key the mic on AM with no audio. If just the final is burned up you can usually still hear the radio transmit when another receiver is placed right next to it. This assumes the driver is still working because this is what you will hear making the slightest bit of output still.

Check the final by lifting the base terminal and using the diode check scale on a test meter. Thermal compound for a CPU is fine for use here. It's often better quality. One last thought. I assume the TX LED comes on when you key the mic and it's not a switching or mic problem? Bias and RF alignment should be performed on the RF stage if you replace the transistor. This is not required if just transistor 41 is bad.

 

[loosecannon]

just to add to what shockwave already posted;

the base leg of the final transistor is the left leg if you are looking at the face of the transistor.
collector is the middle leg, and emitter is the right leg. (B-C-E)
(the driver is the same)

i have tried using a mosfet in the old 148gtl chassis, and the results were not that great.
it takes some experimenting with some resistor and cap values to "dial it in", and i dont think you want to be messing with all that.

you need to find a 2SC1969, and i always get them from an old parts radio.
maybe someone has one that they will sell you cheap. (not me LOL)

do shockwave's tests first to confirm that the final is bad.

you will need a multimeter, preferably digital.
for the procedure on testing the transistors, try this:
Testing semiconductors with analog and digital multimeters

the driver and final are both NPN transistors.

good luck with it,
LC

 

[BOOTY MONSTER]

thanks guys . any suggestions on where to buy those parts from ? ive got to get a new soldering iron too and was just gonna get one from radio shack . i was thinking about this 25 watt one .

http://www.sears.com/shc/s/p_10153_...dering+iron&prdNo=52&blockNo=52&blockType=G52

or maybe this 23 watt kit .

http://www.sears.com/shc/s/p_10153_12605_SPM201668849P?blockNo=59&blockType=G59

is 23-25 watts enough ?

as far as multimeters go will one of these do work for a very green person trying to do the fix himself ?

http://www.sears.com/shc/s/Compare?...artNumber_4=SP100A3135S208294282P&prodCount=4

im liking the the looks of the B951 and the green innova if one of those will do what i need .

thanks again .

 

[loosecannon]

20-30 watts is perfect for PC board work.

just make sure the multimeter has a diode test function.


you wont find the 2SC1969 at radio shack though.
those are getting harder to find.
check ebay.
LC

 

[Big Dummy 123]

Booty ya might wanna get the 2sc1969 from rfparts in San Marcos Calif at least you know its a genuwin Mitsubishi most on ebay are fake couterfits Ben