Hello,
I just picked up a nice 148 GTL ST (Taiwan model) that was sold as a tech special. It was stated that the TX was one channel below receive. This was very true.
It had switches wired up for the standard channel mod, and appears at one time had the clarifier opened, then an attempt was made to redo it. One this model the wires running from the front panel from the Voice-lock pot to the main board are two red and one black wire that attaches to the main board with a three pin header.
I started by un-screwing the work originally done to it and start fresh.
First thing i did was remove the channel mod. While doing this I found a resistor (A 1K Ohm I think) between pin 5 and Pin16. Not sure what that is for.
Next I ran through the standard alignment procedure and got it back to stock. After this the TX was still of one channel, ie. transmit on 36 and receive on 35. Another issue was while AM sounded good, LSB and USB would not tune in.
I turned to the clarifier and looked it over, found that R44 and R174 were intact but D52 was cut, also the wires from the Voice-lock pot were in their original place. I decided at this point to go ahead and open the clarifier. I removed R44, then replaced R174 with a jumper. Most mods call for R175 to be replaced with a 10K resistor, I left this in place. Next I ran the left most red wire of the Voice-lock to the + side of C84 for 8V. Now that is where the mod stops by almost all sites I have seen. The result was that AM is now spot on, SSB is however still 10Kc off, but at least it's a clean signal now. I know from modding 142GTL's you have to ground the opposite side of the Voice-lock pot, doing this brought everything into line. TX and RX are now perfect and it slides about 23Kc!
I re-ran the alignment and let it idle for an hour then went back over it all. Nice and stable and no drifting.
Next I'll do the channel mod correctly.
I have a few questions:
1. Why do none of the mod sites say to ground the black wire on the Voice-lock on the 148? Is this just different on the 148 GTL ST from Taiwan?
2. By not changing R175 to a 10K ohm I still get 23+ Kc slide, what would it be with the change? I'm happy here.
3. What is the resistor on the PLL for?
Thanks es 73!
Mud Duck 577
I just picked up a nice 148 GTL ST (Taiwan model) that was sold as a tech special. It was stated that the TX was one channel below receive. This was very true.
It had switches wired up for the standard channel mod, and appears at one time had the clarifier opened, then an attempt was made to redo it. One this model the wires running from the front panel from the Voice-lock pot to the main board are two red and one black wire that attaches to the main board with a three pin header.
I started by un-screwing the work originally done to it and start fresh.
First thing i did was remove the channel mod. While doing this I found a resistor (A 1K Ohm I think) between pin 5 and Pin16. Not sure what that is for.
Next I ran through the standard alignment procedure and got it back to stock. After this the TX was still of one channel, ie. transmit on 36 and receive on 35. Another issue was while AM sounded good, LSB and USB would not tune in.
I turned to the clarifier and looked it over, found that R44 and R174 were intact but D52 was cut, also the wires from the Voice-lock pot were in their original place. I decided at this point to go ahead and open the clarifier. I removed R44, then replaced R174 with a jumper. Most mods call for R175 to be replaced with a 10K resistor, I left this in place. Next I ran the left most red wire of the Voice-lock to the + side of C84 for 8V. Now that is where the mod stops by almost all sites I have seen. The result was that AM is now spot on, SSB is however still 10Kc off, but at least it's a clean signal now. I know from modding 142GTL's you have to ground the opposite side of the Voice-lock pot, doing this brought everything into line. TX and RX are now perfect and it slides about 23Kc!
I re-ran the alignment and let it idle for an hour then went back over it all. Nice and stable and no drifting.
Next I'll do the channel mod correctly.
I have a few questions:
1. Why do none of the mod sites say to ground the black wire on the Voice-lock on the 148? Is this just different on the 148 GTL ST from Taiwan?
2. By not changing R175 to a 10K ohm I still get 23+ Kc slide, what would it be with the change? I'm happy here.
3. What is the resistor on the PLL for?
Thanks es 73!
Mud Duck 577
