| Author |
Message |
    
Akbowtie
Junior Member
Username: Akbowtie
Post Number: 40
Registered: 5-2005
| | Posted on Thursday, March 23, 2006 - 1:25 am: | 
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Hopefully someone knows whats wrong here.
I have a newer 148, had it set dead keying 2 watts swinging to 6 or so maybe.Always been working great.
Now, accidently put 17 volts to it.
Now it dead keys 10watts, and no modulation at all.
VR10 makes no diff when adjusting it, it's just flat out stuck at 10 watts.
SWRs are 1.3 or less.
Any clue as to what fried? |
Goat373
Intermediate Member
Username: Goat373
Post Number: 192
Registered: 3-2005
| | Posted on Thursday, March 23, 2006 - 7:33 pm: |
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anti-spiking diode...look around the big audio transformer
also maybe a malfuntioning tr-41, but i doubt it...though...even if tr-41 is not causing the problem, with 17 volts i'll bet its cooked...even if not visibly.
(looking at a junker now think of other senarios) |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1339
Registered: 9-2004
| | Posted on Thursday, March 23, 2006 - 9:42 pm: |
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goat is on the right track.
pretty sure it is TR 41 that has to be replaced.
use an NTE152 as a replacement. (better than the original part)
really cheap and easy fix. try it first.
also check the components connected to TR41 (located on the rear right wall of the radio with component side up and knobs facing you)
as one or more of them may have fried.
good luck,
matt |
Akbowtie
Junior Member
Username: Akbowtie
Post Number: 42
Registered: 5-2005
| | Posted on Friday, March 24, 2006 - 1:47 pm: |
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thanks guys i will look at this tonight and see what happens 
I'll let you know . |
Akbowtie
Junior Member
Username: Akbowtie
Post Number: 43
Registered: 5-2005
| | Posted on Friday, March 24, 2006 - 11:12 pm: |
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where the heck is TR41 ??? I found Tr42 in that area but no TR41.
This is a NEW 148, not a ST but a gtl.
I'll keep looking. |
Akbowtie
Junior Member
Username: Akbowtie
Post Number: 45
Registered: 5-2005
| | Posted on Friday, March 24, 2006 - 11:15 pm: |
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someone one saying the AM regulator transistor ??
which would this be ? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1345
Registered: 9-2004
| | Posted on Saturday, March 25, 2006 - 10:43 pm: |
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akbowtie, i just found an old cobra service bulliten about the 148gtl.
i think you're going to like this.
it states that one symptom of the regulator IC (MB3756) being blown is a high AM dead key with little or no modulation, and weak or no receive.
the fix involves replacing the IC, and a diode change.
here it is:
replace IC 4 MB3756 (located on the right hand wall of the chassis)
replace D44 with 18.2 volt zener diode.
solder the old D44 (if its still good) from pin 1 to pin 2 of the new MB3756. (banded end to pin 2)
if D44 was no good, use an SR1K2 diode, or NTE116, or any 1amp rectifier diode.
that should do it!
you should still replace TR41. (it may be a different part number on the new 148gtl's, but its still in the same place.
its the only three legged thing bolted to the same wall as the voltage reg. (MB3756) and the audio chip (TA7222p).
it will look just like the driver and final transistors, but will be labled C1419 or D1135. (maybe they use something else now, but either way, replace it with an NTE152 or a GE 66 if you can find one. (its the better part)
dont forget to use the heatsink compound!
the transistor im referring to is the AM regulator transistor.
hope this helps,
matt |
Akbowtie
Junior Member
Username: Akbowtie
Post Number: 47
Registered: 5-2005
| | Posted on Sunday, March 26, 2006 - 2:58 pm: |
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wow thanks again !! We shall see what happens ! |
