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JC Penney 6241

Smokinone

Smokinone

WDX-3820
Jun 24, 2020
827
1,046
153
Southern Nevada
I am working on this 6241 and it has a channel expansion done to it as I received it. What it has is pin 10 & 11 shorted together to get channels (14) 27.445 thru (27) 27.595. That works OK, as does the (1) 27.605 thru (40) 28.045 mod.

What I would like is (12) 27.425 on up. I think this can be obtained by going or shorting from pin 1 or 8 to pin 10, instead of the 10 to 11 it has now.
Am I thinking wrong here?

I just don't want to smoke the 5104, and I really don't want all the channels that a rotary switch would give.

Thanks.

SM5104_JCPenney.jpg
 

Your wish for a "42 and up" won't quite work with this chip. The PLL's inputs are binary, and you can only change frequency by a factor of 2,4,8,16, 32 or 64.

Bridging pin 10 to pin 11 won't damage the PLL chip. It will add 32 channels, topping out at 27.595, or so my bench notes tell me. The date on my bench file is 2007.

And you have already discovered the +64 that starts with 27.605 at channel 1.

And that's the quirky part of expanding a PLL with binary inputs. Decades ago before frequency counters got cheap, this kind of mod would be sent home with a printed list of what frequency was found where on the channel display, and the "extra channel" switch positions.

The so-called "10-meter" radios with a 40-click channel selector contain a pair of chips that do the binary arithmetic needed to put all 40 channels in a row on multiple bands. This radio just doesn't contain that feature.

73
 
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Thanks. 10 & 11 were already bridged for a 44 & up. I was looking at the rotary switch mod that shows the 42 and up with the #3 position on the rotary with the 5104 PLL. It looked like that was bringing 10 high to get it. I don't know enough about it really, and I don't want to make a bonehead move. I don't mind asking stupid questions as opposed to making stupid mistakes:)
I think these might have had the PLLO2A in some of these radios as well, but not sure.

Thanks again.


SM5104 channels1sm.jpgSM5104 channels2sm.jpg
 
I found this too, which suggests something different, unless I'm reading it wrong.

This is for radios that use the SM5104 PLL​



The PLL is a binary type, to increase the radio up to 28.000 you just need to pull pin 8 high and pin 9 low, this will increase the frequency range by 128 channels (up to 28.245 on channel 1).


If this is too high you could just pull pin 10 high instead, this will increase the range by 64 channel and move the radio up to 27.605 on channel 1 through to 28.045 on channel 40.


If this is too low pull pin 11 high as well as pin10, this will give you and increase of 96 channels between channels 1 and 27, so it will cover 27.925 on channel 1 to 28.235.



To control a pin cut its track and add a 4.7 KOhm resistor across the cut.


So to pull a pin low cut its track and add a 4.7 KOhm resistor across the cut, then jumper (through a switch) the PLL pin to pin 16 (this is the ground pin), or to pull it high jumper to pin 1 (this is the + supply).



Another reason I ask questions, I get confused by all the variations.
 
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There's a truth chart in Sam's 235. It looks a bit odd in that channel 1 appears to be all 0's. Until you realize that pin 8 has binary weight of 128 and is tied to +5V, and the N-code for channel 1 is 128. So there's no point in isolating pin 8, as it's already at a logic high (+5V).

Why does the truth chart show all 0's? They didn't include pin 8 because it's tied high and never changes. Schematic shows pin 8 tied to +5V as well.

The original author may have had AM only radios in mind.
 
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That's the stuff that I don't really understand. I've got the Lou Franklin books and several others, and I just can't get it to click.
On a whim, I disconnected the pin 11 from 10, and put it to switch into the 4.8V, to go high, and I now show 42 on channel 12. So pin 10 high does the 42 through 59. I'm happy.
I appreciate the help, just knowing I couldn't smoke the PLL was a plus. I wish I had more knowledge of how all this worked, but thankfully people here do.

Thanks.

Here's a nice Sears version of this in the box in Louisville if anyone is near there. I don't know who the seller is.

louisville.craigslist.org

Sears Roadtalker CB 40 CH SSB - electronics - by owner - sale

Sears RoadTalker 40 channel SSB base/mobile. These are extremely well-built radios and one of the best 40 channel chassis ever made. No mods or tweaks have been done to this radio. Great condition...
louisville.craigslist.org
 
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1660096978771.png

Here's my Roadtalker 40 SSB (same radio with different faceplate & switches). The knob next to the freq counter is a 16 position 4-bit binary encoding rotary switch hooked to pins 8-11 of the SM5104.. It also has a 10khz slider mod on the clarifier..
The range of the VCO in this radio seems to be about 2mhz (give or take 100khz or so). So, even though the PLL will produce IF channel sets from quite a range, using all 16 combinations of the states of all 4 high order binary input bits, The VCO will only actually lock from about 26.1mhz to 28.1mhz. You can adjust that range up or down by tuning T302, but you're really not going to widen it any..
 
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Just picked up one of these on FB Marketplace. A channel mod was already done with a dpdt switch, center off. Got is super cheap because someone had try to pry the right side of the metal faceplate off. I have glued it back in place and the glue is curing. I will post pics after I put it back together and figure out the channel mods. I believe one position takes it up 128 channels as I heard some CW in one position. Thanks for posting the charts.

One problem I have encountered with the cybernet w PLL02a is the VCO shuts down quickly when you attempt to modify them for 10 meters. This chassis seems a bit more forgiving.
 
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Those DDS VFO's are cool ! The one in your picture was I believe being made and marketed by a guy from Brazil. Pretty sure he's no longer selling them, and I have a feeling not too many were actually produced for sale, though I could be wrong.
I remember a thread, possibly on here, discussing them. Must have been a year ago or so.......
It would be great if they became available again!
 
Nice ! Are they a fairly straightforward install ? Or do they require advanced electronic skills ?
 

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