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Message |
    
Rascal853
New member
Username: Rascal853
Post Number: 1
Registered: 2-2004
| | Posted on Saturday, February 04, 2006 - 11:49 pm: | 
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i just recently got a used 139xlr and it has no mod or dead key so i open it up and find that d25 and r153 are smoked can any one tell me what the value of r153 is and why it would be burnt? burnt beyond recognition.. hope nothing else was hurt. thank for reading
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1154
Registered: 9-2004
| | Posted on Sunday, February 05, 2006 - 1:14 am: |
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rascal, this is a very common problem with this chassis. the reason R153 burnt out is because the transistor right in front of it that is heatsinked to the thin metal sheilding does not get enough heat dissapation and it is a cruddy part to begin with.
the transistor is a 2SC1419. replace it with a NTE152. you will find about three more of these 1419's around the board and on the power supply board. replace them all!!!
on the transistor mounted in front of R153, dont put the new transistor back in the same spot.
instead, drill a small hole in the aluminum heatsink on the back of the radio and mount the new one there. make sure you use the little insulator for the screw and use the mica insulator on the back, and use heat sink compound. just run wires from the old location to the new one making sure to get the leads correct.
i will check when i get home tonite and post tomorrow, but im pretty sure that R153 is a 47ohm resistor. i would use a 2 watt or bigger replacement.
i will check on D25 also as i cant remember what that part is.
for now, find the NTE152's and order them. do not bother replacing the resistor until you have the new transistors, you will blow the new one too.
i will also post a few other common problems/ cures for this chassis.
great radio, one of my favorites! they can be converted to go from 26-28mhz!
look for more tomorrow evening,
matt |
Rascal853
New member
Username: Rascal853
Post Number: 2
Registered: 2-2004
| | Posted on Sunday, February 05, 2006 - 10:24 pm: |
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matt,
thanks for the quick response,do you think this could of hurt any other parts? i found the NTE152 and i will order them tonite hope to get them before this weekend so i can get this thing up and running. this already has the channel conversion done to it but i havent played with it much since i cant talk on it. will these new transistor help the audio output any? thank's for your reply ill wait to hear back from you!!
Dennis
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1165
Registered: 9-2004
| | Posted on Sunday, February 05, 2006 - 10:54 pm: |
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yes, replacing these transistors should improve the audio output a bit. basically, returning it to normal.
unless you find some burnt foil traces on the solder side of the PC board, i think you're OK.
D25 is a 7.5 volt zener diode. any brand you can find with this value should work.
R153 is a 56 ohm 2 watt resistor.
replacing all three parts should do it.
since that chassis is getting older, i would recommend replacing all the electrolytic caps.
dont worry so much about the others, bt the electrolytics dry out faster.
this will make a big difference in how good the audio sounds on recieve and transmit.
lots of mods out there on the net for this one; better to check here before attempting them.
good luck,
matt |
Rascal853
New member
Username: Rascal853
Post Number: 3
Registered: 2-2004
| | Posted on Tuesday, February 07, 2006 - 10:58 pm: |
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matt ,
thanks again for all the info i've ordered all the parts and got them on the way hope to have them by the begining of next week. foil on the back of the board looks to be ok, other than those few burned out pieces the radio looks to be in fairly good shape. is there any mods you might recommend for this radio? thanks again ill let you know how everything goes..
Dennis |
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