858PLL 23 Ch. to 40 Channel "update".

[unit_399]

Leapfrog -
I think I can show you how to mod the 21X pLL circuit to get 40 channels (and maybe more). Set the radio to channel 1, and check pins 13 thru 20. Let me know which pins are at logic 1 (5.0 vdc). Do the same for channel 23. Get back to me with the results. 73s.

- 399

 

[LeapFrog]

[photo="medium"]4346[/photo] .

Thank You Unit_399
Best Regards
-LeapFrog


EDIT: Pins 20 & 21 are tied together,
Interpreted from here for the 21X / trc-452 (second to last page/schematic diagram).
Pin 13 = 1A
Pin 14 = 1B
Pin 15 = 1C
Pin 16 = 1D
Pin 17 = 2A
Pin 18 = 2B
Correct up till here I believe.
Pin 19 = ? looks to be grounded
Pin 20 = ? tied to pin 21
Pin 21 = ? tied to pin 20
Pin 22 = 3B
Pin 23 = Ground
Pin 24 = Program Output

 

[LeapFrog]

On the 21XLR pins 20 & 21 are separate and pin 22 is grounded.
On the TRC-452 this is not the case, and the layout matches that of the 21x.
(This leads me to believe I can do the mod just from the channel select switch, but i'm not sure)

Both radios (trc-452/21xlr) use the 858pll and are 40 channel rigs so it looks like 40 channels can be done in more than one way with this chip.

 

[unit_399]

Leapfrog -

To get the full 40 channel spread on your 21X, first get the following parts together:

2 - 1N914 diode
4 - 4.7Kohm - 1/4 watt resistor
1 - single pole double throw CENTER OFF switch
1 - single pole single throw switch

Cut the traces to pins 13, 20, 21, and 22 as close to the pin as possible, and bridge the 4.7k resistors across the cuts. Wire up the diode and the SPDT switch as shown in the diagram. Closing the switch will give you channels 26 thru 40 (except for the skips) on channel selector positions 9 thru 23.

To get the skips, as well as channels 24 and 25, connect the spst switch to pin 13 as shown. This will act as a +/- 10kc jump. Put the rig in the 23 channel mode. On channel selector position 22, putting pin 13 high gives you Channel 24. Selector position 23 with pin 13 low gives you channel 25. Use a freq counter to find out how to get all of the other skips.

Get back to me and let me know how this works out. Good luck and 73s.

- 399

 

[LeapFrog]

Excellent Unit_399, thank you!
I have hit a snag, when I tried the info I first posted in the thread I used the last two 4.7k resistors I had, a 1/8 watt and 1/4 watt 4.7k ohm even though one was noticeably bigger and looked goofy. Now I only have one (used one) left on my bench.

Is the resistor value super important or could I get away with say, 1Meg Ohm resistors in place of the 4.7K? And I don't have any 1N914's so I will use 1N4148's, this should be okay for the diodes I think, but i'm unsure of the higher resistor value inplace of 4.7k, this is just a pull up/pull down resistor?

So closing the SPDT brings ground to the anode of the diodes, and 4.97v to pin 22 at the same time and 21, 22 will never have continuity through the switch, correct?
Where does the center-off part come into play? I envision a switch with either on/off no middle position, I don't see why a center-off switch is called for.
When the switch is off, and the radio is running in 23 ch. mode pins 20,21,22 all run through the resistor to the original trace?
For the sake of clarity, I could use two separate spst switches, one for adding 4.97v on pin 22, and another to switch pins 21/20 to ground & as long as I switch both at the same time to an "on state", I make could do without the spdt?

Thank You

73

 

[unit_399]

Is the resistor value super important or could I get away with say, 1Meg Ohm resistors in place of the 4.7K?

So closing the SPDT brings ground to the anode of the diodes, and 4.97v to pin 22 at the same time and 21, 22 will never have continuity through the switch, correct?
Where does the center-off part come into play? I envision a switch with either on/off no middle position, I don't see why a center-off switch is called for.
When the switch is off, and the radio is running in 23 ch. mode pins 20,21,22 all run through the resistor to the original trace?
For the sake of clarity, I could use two separate spst switches, one for adding 4.97v on pin 22, and another to switch pins 21/20 to ground & as long as I switch both at the same time to an "on state", I make could do without the spdt? 73

Use either a 4.7k or a 5.1k nothing else. the 4148 is ok. You can use 2 separate switches for controlling pins 20/21 and 22, but I I would stick with the double pole single throw for simplicity. They're available everywhere.
You need the single pole single throw CENTER OFF to control pin 13. Having a center-off position lets pin 13 change according to the switching in the channel selector. You only need to use the switch to get the "skipped" channels 3A, 7A, 11A,15A, and 19A.

 

[LeapFrog]

I will locate some 4.7K resistors and I will most likely not install the switch for the skipped channels as I will never tune into those channels, thanks for breaking this all down for me and explaining what the "skipped channels" are, I appreciate your help.

Results will be posted, after I get the resistors.

Best Regards.
-LeapFrog

 

[unit_399]

Without the skipped channel switch you will not get channels 29, 34, or 39.

 

[LeapFrog]

Thank You, Unit 399 man you kick @$$! The locals ragchew on ch. 28 often
so I don't think I will miss 29, 34, or 39.

I will probably end up adding the "switch for skips" just to make it a complete mod though.

I am going to find the resistors come hell or highwater!

I can't wait to do this. My first frequency expansion mod, made possible by Unit 399 and WWDX.
Shout out to CK for dropping some bcd knowledge, I just need to learn how the truth table was made so I can do this for myself in the future, I'm sure all the knowledge is available in data sheets and service manuals but, looking at it all at once I kind of got lost in the "white noise" of my mind lol with all the numbers, I'm sure it's moderately difficult and I'm just not sharp enough to grasp it all in a glance.



Best Regards
-LeapFrog

 

[LeapFrog]

 

[Tallman]

Looking forward to see the results. Might do that to some of my older cb gear as well.

All of that information gets kind of overwhelming when it hits all at once.