Improved
bandwidth |
|
| Part designation |
Old value |
Correct value |
Reason |
|
|
|
|
| Phase-lock-loop |
|
|
|
| L507, or R521 |
4.7 or 1.0
microhenry choke, or 4.7K ohm resistor |
3.9K ohm 1/4
watt |
For
improved PLL lock up time during scan and during PTT actuation; reduce or eliminate ping
during PTT actuation; eliminate spurious PLL which causes no RX or TX when the VCO volts
are below 4.4vdc, TX tone deviation is more even across the band |
| R522 |
Jumper, or
100 ohm resistor |
8.2K ohm 1/4
watt |
| R523 |
5.6K ohm |
2.2K ohm 1/4
watt |
| R524 |
6.8K ohm |
5.6K ohm 1/4
watt |
| R526 |
10K ohm |
6.8K ohm 1/4
watt |
| C513 |
.1 microfarad
cap |
.047
microfarad |
| C520 |
.1 microfarad
cap |
.022
microfarad |
| As needed IC502 |
TL071, CA3140 |
CA3130 or
equivalent |
Replace only
if the VCO volts are still not stable after all above mods are performed |
| R527 |
39 ohm |
15 ohm 1/4
watt |
Increase the
maximum VCO voltage |
|
|
|
|
| VCO/Audio filter board |
|
|
|
| Q202 |
|
020 or
4811-020 |
Improves RX and TX bandwidth |
| Q203 |
|
Red top or
MPS-H10 |
Improves RX and TX bandwidth |
| C234 |
4.7microfarad
tant. or .2 microfarad CD |
.47
microfarad ceramic disk |
Faster tone
decode ( the .2 microfarad cap becomes leaky) |
| C235 |
4.7microfarad
tant. or .2 microfarad CD |
.47
microfarad ceramic disk |
Faster tone
decode ( the .2 microfarad cap becomes leaky) |
|
|
|
|
| TX Excitor |
|
|
|
| On solder side of main board across L506 |
680 ohm 1/4
watt resistor |
1.5K ohm 1/4
watt - Also try removing it |
Increase TX
band spread |
|
|
|
|
| Receiver |
|
|
|
| L409 |
39 microhenry
choke |
3.3K ohm 1/4
watt |
Eliminates AM
interference, Improves squelch thresold settings |
| Across L405 |
680 ohm
resistor |
5.6K ohm 1/4
watt |
Improves RX
bandwidth |
| On solder side of main board across Y402 |
1K ohm
resistor |
Remove |
Not needed as
it causes various RX problems |
|
|
|
|
| Reset circuit |
|
|
|
| R418 |
|
1.2K ohm 1/4
watt |
|
| R419 |
|
1.2K ohm 1/4
watt |
|
| R420 |
|
10K ohm 1/4 watt |
|
| CR4 |
|
1N5238 (6.8v
Zener diode) |
|
| Q418 |
|
MPS952-2
transistor |
|
| Q419 |
|
MPS952-2
transistor |
|
| Add to solder side of main brd |
4.7
microfarard 10 volt electrolytic capacitor |
+ to C of
Q419, - to grd |
|
|
|
|
|
| PA board (older boards only) |
|
|
|
| Added to top or bottom of PA brd at Base of Q301 to ground |
|
47pf ceramic
disc capacitor |
Eliminates the regeneration of RF after the PTT button is released. |
|
|
|
|
| Add to the power plug inside the radio - + to red wire, - to chassis
ground |
|
6800
microfarad 16vdc Electrolytic capacitor |
Reduces EMI
caused by altenator, blower motors, etc. - It is necessary if you are maximizing the
bandspread |
| Ham
modifications - Minimum operating bandwidth of 144 to 152MHz |
|
| Important note:
All of the above modifications must be performed to achieve maximum band spread |
|
|
|
|
|
| VCO board |
|
|
|
| C208 |
6.8pf |
12pf |
|
| C210 (as necessary) |
8.2pf |
15pf |
|
|
|
|
|
| Receiver |
|
|
|
|
|
|
|
| TX excitor |
|
|
|
| C538 |
3.9pf |
5.6pf |
|
|
|
|
|
| PA board |
|
|
|
| C303 |
82pf |
100pf |
|
|
|
|
|
| Self - Quieting
on frequencies like 154.515, 154.980, |
|
| Add to solder side of main brd in parallel with Y501 |
|
3.3K ohm 1/4
watt resistor |
|
| Add to solder side of main brd in parallel with C543 |
|
12pf CD
capacitor |
|
| As necessary, cut the bottom metal plate so when installed the front
edge is flush with the ground leads of C545. Add a piece of solder wick from the front of the
metal plate to one of the ground leads of C545. |
