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vr7 on 148 gtl help

1iwilly

Sr. Member
Dec 7, 2008
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ok so the 148 gtl i have made in Taiwan has vr7 which i believe is am modulation but i can't verify because my sams don't show or says anything about vr7 or on schematic when i turn it, either way, i don't see any changes in the audio or watt meter and yes all limiters are intact and working reason i say working is if i clip r131 watts up on meter where r130 is i have a white wire going from it to vr7 and d57 next to it. i check vr7 out of the circuit and it goes up and down d57 check good on diode meter anybody here have an updated 148 gtl side mike schematic for me to check why vr7 not working ?? thanks

also problem #-2= while checking wattage with dummy load when i set swr cal on radio internal meter to where you set it then to swr instead of needle barely moving it move to what i believe 1.2 ?? look at pics any adjustments for it.
 

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ok after further inspection i found that a few yes a few TR transistor look like they're put in the wrong way look at pic you see tr26 &TR4 are facing the wrong way am i correct ?? and a few other too
 

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I doubt they are wrong way 'round , however if you care to check you can do the homework.
Identify the position on the board
read the silk screen and identify the leads/holes (E,B.C)
compare with schematic.
You have the manual now so there is no excuse not to .
Even if you find all is well it's good practice .
 
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i'll take more pic to show that there is a problem some face the right way some don't the lettering suppose to face the cut on the board



I doubt they are wrong way 'round , however if you care to check you can do the homework.
Identify the position on the board
read the silk screen and identify the leads/holes (E,B.C)
compare with schematic.
You have the manual now so there is no excuse not to .
Even if you find all is well it's good practice .
 

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i'll take more pic to show that there is a problem some face the right way some don't the lettering suppose to face the cut on the board

The transistors that were installed at the factory may be different than what the designer originally called for. This sometimes means the legs will be in a different order. One may be EBC, and another CBE for example. The parts will be functionally equivalent, they'll just look "wrong" against the silkscreen on the board.

This can happen in repairs, too. Especially when replacing parts that are no longer made. Even seen some where legs are crossed with one leg having heat shrink around it to prevent a short.
 
ok so that would mean that when i put TR24 back it was removed i put it in the way i always done it but looking at data sheet the radio has 2sc711 instead of 2sc945
look at pics pin out is diff so i will have to remove TR24 and 360 it thanks TM86


The transistors that were installed at the factory may be different than what the designer originally called for. This sometimes means the legs will be in a different order. One may be EBC, and another CBE for example. The parts will be functionally equivalent, they'll just look "wrong" against the silkscreen on the board.

This can happen in repairs, too. Especially when replacing parts that are no longer made. Even seen some where legs are crossed with one leg having heat shrink around it to prevent a short.
 

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ok that fix the issue vr7 is back working again thanks for the help guys now to look at issue #2 swr calibration
 
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1iwilly those SWR meters never work very well.

you can get them to read accurate at an SWR of 3, and then put it on a known good dummy load and watch it read an SWR of 1.5.

best you can do is decide which SWR you want to read correctly and set it there.

i don't believe the 148's had a variable adjustment for this, but if you look near the SWR meter section, you should see a resistor in series with a diode.
make this resistor variable, and you should be able to set the SWR meter to match up with an external meter. of course, it will only read that SWR correctly though.
LC
 
Easiest way to check?

Locate your SWR spot - that little coax thingy, well - cable "ferrite" or even real coax, but look for R52 and R53...
upload_2020-8-24_8-44-20.png

Those values change thru the years, the ST units especially - anywhere from 560 ohms, on down to as low as 150 / 180 ohms for BOTH sides of the bridge.

So due to the size of AWG, the critical locations on the sense wires and the sheer variability of the whole mess, you can see why they did use these values to "tune" their bridge to the meter to read approximate - not exact, but approximate.

Good luck...
 

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