Pro 2021 speed mod?

[fshndean38]

I have found a modification to speed up the scan rate on the pro 2021
however it is a bit confusing.It says to cut the leads on resistor
R147 and solder in a 15k ohm resistor. Then at the bottom it says you
are not replacing the R147 resistor a 39k ohm resistor i think. You
are adding 15k ohms to the existing resistor,so my question is are you
cutting the leads to one side of the resistor and adding the 15k ohm
resistor in-line and if so exactly how would you do this. ex. color
codes on resistor placed the same direction ?

Also any new panel light replacement ideas ?

 

[LesWurk]

Remember doing speed mod for the Pro 2021 that involved changing a ceramic resonator. Results were disappointing. Think I undid it. Also did the mod to add 800mhz. Could program it in but completely deaf. Still have the Pro 2021 running 24/7 for many years, mostly for local fire. Display backlight dead for a long time. The same principle of display backlight as the Pro 2006 works, so search for the replacement panel options there.

 

[DickH]

I have found a modification to speed up the scan rate on the pro 2021
however it is a bit confusing.It says to cut the leads on resistor
R147 and solder in a 15k ohm resistor. Then at the bottom it says you
are not replacing the R147 resistor a 39k ohm resistor i think. You
are adding 15k ohms to the existing resistor,so my question is are you
cutting the leads to one side of the resistor and adding the 15k ohm
resistor in-line and if so exactly how would you do this. ex. color
codes on resistor placed the same direction ?

Also any new panel light replacement ideas ?

I can understand your confusion. If the 39K resistor is part of a timing circuit you would need to reduce it's value to increase the speed. Before cutting anything, try holding another 39K resistor across it. That would half the value. See if that increases the speed.

 

[pro92b]

The PRO-2021 has no 800 MHz front end circuitry and will never receive 800 MHz. The CPU can be fooled into displaying 800 MHz frequencies though.

The speed modification appeared in the World Scanner Report authored by Bill Cheek. He indicated that R147 can be lowered to about 10K and the radio still works. To get about 10K, solder a 15K resistor across (in parallel) with the existing 39K resistor. Expect the channel delay time to be shortened with this modification. If the radio doesn't work well with the 15K resistor, remove it and try 33K.

 

[AC9BX]

You don't cut anything for the speed mod. You add a resistor in parallel to the other. Resistors in parallel have a lower resultant value than each one. A 39k and 15k in parallel equals 10.8k. By doing it this way you can remove it easily. I swapped out the resistor. This mod will not give you dramatic results but the radio will scan noticeably faster. Reducing the value further causes the radio to scan faster than the other sections can work with, it will miss things.

There's 2 parts to the 800MHz mod. One is removal of a diode. This enables the band on the CPU. The other is to enable the UHF filter section. One method out on the web is to add a 10k resistor at the shift register. This is incorrect and does nothing. The correct value is 10 ohms. Pin 13 if I recall. This prevents shorting the pins and allows two outputs on the chip to select the same section. It does work, that is, it does engage the UHF section when tuning 800MHz. However, 800MHz performance is very bad. It is not designed for this so even though it can be switched in it doesn't work well at all. The frequencies are out of the effective range of the downconverter. An option would be to build a new section for the band. Just get a newer scanner.

I would perform the speed mod. It is pleasant even though it reduces the delay time a bit. I would not mess with any frequency range conversion. Even if you 'restore' VHF frequencies on a US model the rest of the unit is not tuned to perform well. The European/Aus version has different alignment for VHF-MID.