UPD858 Chip Mod

[jonindiana]

Ok hope someone can point me towards a good mod here.I have a Radio shack TRC458 Base that has never been modded.I need to mod it for channels so it can at least go down to 26.765 and up to 27.855.I have read you need to add like 5 volts to certain pins to get the below channels.I have looked at the mods on the net and dont know if they work.Has someone done this mod with good results and could pass me the mod?Any help would be great.

[ramblingman]

hi there,got one question,does your radio have ssb,or is it am only

[jonindiana]

yes it has ssb thanks for the reply

[ramblingman]

hello once again. o.k. heres what the book says.first isolate pin 19 from ground.do this by making a small cut with a x-cto knife.be sure to completely isolate it from ground.next add a 4.7 k resistor across the cut land pattern.then locate pin 21,and do the same thing,carefully isolate pin 21 from ground with the x-acto knife.then add a 4.7 k resistor across that cut pattern.then you will need two toggle switches,one single pole double throw center off switch,and one single pole single throw switch.the single pole switch goes in conjuction with the cut pattern of pin 21.the single pole double throw switch wires as follows.top pole of switch to pin 20.center pole of switch to pin 21,below cut pattern.bottom pole of switch goes to pin 19 above the cut.the 4.7 k resistor from pin 21 needs to go to ground also,you can pick that ground up below the cut of pin 19,the same point as your pin 19 resistor is grounded.you will really need a freq, counter to know exactullay where you are,but here is a good guide.with the single pole switch(switch 1) up and the double pole switch(switch 2) in the center position,you will have normal channels.with switch 1 up and switch 2 up,starting at channel 8=27.455-channel 40=27.805,with switch 1 up and switch 2 down,starting at channel 8=27.855 to channel 20=28.005,with switch 1 down and switch 2 up,starting at channel 8=26.455 to channel 40=26.805,with switch 1 down and switch 2 down staring at channel 8=26.855 to channel 20=27.005.and with switch 1 down and switch 2 in the center starting at channel 11=26.805 to channel 40=26.405. a slight adjustment of the v.c.o. might be nessacery to get all the channels to pop in.i believe you said your radio was a realistic trc-449,on that radio the v.c.o. adjustment is l-17 and the transmit balance adjustment is l-37.if it was me id just try it first without messing with the v.c.o.then if you have to tweak it alittle,it is very sensiitive.and you really need a freq,counter to get in locked in right.just adjust that as a last resort.if all the channels dont lock in..good luck with your mod,i hope this helps.

[jonindiana]

Thank you Rambling Man I will give it a try this weekend.I have some mods for the 8719 PLL that have not been in any books to get down to 26.175 and up to 28.045 if you need the mods let me know.I have a 2000GTL a Madison and a Grant LT that have the mods in and they work great.

hello once again. o.k. heres what the book says.first isolate pin 19 from ground.do this by making a small cut with a x-cto knife.be sure to completely isolate it from ground.next add a 4.7 k resistor across the cut land pattern.then locate pin 21,and do the same thing,carefully isolate pin 21 from ground with the x-acto knife.then add a 4.7 k resistor across that cut pattern.then you will need two toggle switches,one single pole double throw center off switch,and one single pole single throw switch.the single pole switch goes in conjuction with the cut pattern of pin 21.the single pole double throw switch wires as follows.top pole of switch to pin 20.center pole of switch to pin 21,below cut pattern.bottom pole of switch goes to pin 19 above the cut.the 4.7 k resistor from pin 21 needs to go to ground also,you can pick that ground up below the cut of pin 19,the same point as your pin 19 resistor is grounded.you will really need a freq, counter to know exactullay where you are,but here is a good guide.with the single pole switch(switch 1) up and the double pole switch(switch 2) in the center position,you will have normal channels.with switch 1 up and switch 2 up,starting at channel 8=27.455-channel 40=27.805,with switch 1 up and switch 2 down,starting at channel 8=27.855 to channel 20=28.005,with switch 1 down and switch 2 up,starting at channel 8=26.455 to channel 40=26.805,with switch 1 down and switch 2 down staring at channel 8=26.855 to channel 20=27.005.and with switch 1 down and switch 2 in the center starting at channel 11=26.805 to channel 40=26.405. a slight adjustment of the v.c.o. might be nessacery to get all the channels to pop in.i believe you said your radio was a realistic trc-449,on that radio the v.c.o. adjustment is l-17 and the transmit balance adjustment is l-37.if it was me id just try it first without messing with the v.c.o.then if you have to tweak it alittle,it is very sensiitive.and you really need a freq,counter to get in locked in right.just adjust that as a last resort.if all the channels dont lock in..good luck with your mod,i hope this helps.

[booger351]

what is the mod for the AM version, I have a 89xlr, I think it is: isolate 19 and 19 to center pin, ground to one and 5v to other.
Let me know if this is right.
Thanks.