TRC-459 help needed

[KEWB-N1EXA]

Its your first option ( SDR-DEVICE)

The signal is too hot and just is going to be seen everywhere on the spectrum.

 

[press1280]

Turn your gain down on the SDR your too close also you don’t need an antenna on the SDR being that close either.
Also transmitting into a dummy load would be better for testing purposes.

Removing the sdr antenna did the trick, thanks!

the trc-459 is transmitting (likely also receiving) on 26.305 (approx) MHz on channels 1 and 40 and presumably all channels in between. The background noise never changed on any channel so I suspected it wasn’t changing channels.
I tried in Ssb mode and that seems to work, again just on the 26.305 frequency which is well under channel 1.

 

[KB4MSZ]

66 channels below channel 1. Odd. I could see it being 40 channels low, but 66?

 

[KEWB-N1EXA]

Removing the sdr antenna did the trick, thanks!

the trc-459 is transmitting (likely also receiving) on 26.305 (approx) MHz on channels 1 and 40 and presumably all channels in between. The background noise never changed on any channel so I suspected it wasn’t changing channels.
I tried in Ssb mode and that seems to work, again just on the 26.305 frequency which is well under channel 1.

Looks like the connection between the channel selector and the PLL programmer input have been lost. This could be a bad wire or ribbon cable or some golden screw driver broke them to change the programming.
This is where the fun begins!

 

[KB4MSZ]

Or where it ends.

 

[KEWB-N1EXA]

Or where it ends.

This is where you google the schematic and service manual...Radio shack is pretty common out there.
start learning and have some fun or frustration...or just be one of those guys that just credit cards stuff
and learns nothing!

Sounds like the clock frequency ( crystal) is way off or changed or the inputs to the PLL processor are screwed up and the
radio is a dead duck right now but the good thing is it still transmitting and receiving...Justs its way out of the CB band.
Id look up the PLL chip and see if you can +5v or ground the channel inputs and see if it changes frequency. That would show the PLL
is running and its the Channel selector not talking to the Chip. The Channel Numbers(1-40) have nothing to do with the binary input to the chip
seeing most cbs have a multi level rotary switch for the channel selector.

On my Cobra 148 you just add a switch with +5 and GND to pin 12 of the PLL Chip and you can go over CH 40 to listen to the free band
locals who spent all kinds off $$$ for export radios or Ham Rigs.

Pete N1EXA

 

[press1280]

The schematic is online but I may get the sams manual for it, it’s only a few bucks and may have some good info

 

[press1280]

Quick question. I only see 5 or 6 crystals here. With my 23 channel rigs there were like 11 crystals.
How does this get 40 channels out of 6 crystals?

 

[KEWB-N1EXA]

Quick question. I only see 5 or 6 crystals here. With my 23 channel rigs there were like 11 crystals.
How does this get 40 channels out of 6 crystals?

Off the top of head now..
Go back to the 1970s and 23 channel radio's there was no processor what the did in was took those 11-12 crystals and mixed the
frequencies in multiple pairing off the rotary switch it was called Phase lock loop...Infact there really was 24 channels thats what the dot is for
on the radio channel sector on my old ray jeffereson 705 you could nudge the selector between 23 and the Dot and get 24 or 22A as we call it back then...
in the 1980s the PLL processor came along it used 1 crystal to feed the Chip and then the channel selector would in binary code change the 4
inputs and you could add or subtract off the crytal generating the PLL Frequency...you can change the crystal or add a kit to get the radio to
go above or below the CB band...example Free band or 10 meters but the performance starts to roll off...

Now 6 crystals???? I dont know...I ll have to look at the Schematic?

These could be for Filter circuits ...dont know...ll google your radio.

Peter N1EXA

 

[KEWB-N1EXA]

Quick question. I only see 5 or 6 crystals here. With my 23 channel rigs there were like 11 crystals.
How does this get 40 channels out of 6 crystals?

http://www.cbtricks.com/radios/realistic/trc_459/graphics/realistic_trc_459_sm.pdf

Page 6 explains how the processor works its a crystal driven PLL and the AM and SSB are Crystal controlled Filters.

Boy that's a battle station inside looking at the Schematic...

Pete N1EXA

 

[KEWB-N1EXA]

http://www.cbtricks.com/radios/realistic/trc_459/graphics/realistic_trc_459_sm.pdf

Page 6 explains how the processor works its a crystal driven PLL and the AM and SSB are Crystal controlled Filters.

Boy that's a battle station inside looking at the Schematic...

Pete N1EXA

Page 27 is a good place to start trouble shooting your PLL frequency issue...

Pete N1EXA

 

[KEWB-N1EXA]

Page 27 is a good place to start trouble shooting your PLL frequency issue...

Pete N1EXA

Page 41 lists the 6 crystals 1 is the Processor and the other 5 are Crystal filter frequency generation.

Pete N1EXA

 

[prcguy]

I would start with page 20 and the truth table checking for the correct high and low on IC-1 from the channel selector switch.

 

[KEWB-N1EXA]

I would start with page 20 and the truth table checking for the correct high and low on IC-1 from the channel selector switch.

First line on page 27 ...Refer to page 20 for frequency code chart !

 

[press1280]

I would start with page 20 and the truth table checking for the correct high and low on IC-1 from the channel selector switch.

Can you elaborate on that? I’ve never checked one of these

 

[prcguy]

On the chart look at the far right side and it lists pin numbers on the PLL chip and if they will be in a high or low state for each channel. A low state (0) would be near zero volts and I assume a high state (1) would be near 5v or at least above 3v. This will tell you if the channel selector switch is providing the right info to the chip and if someone might have done a mod to change the frequency range.

Can you elaborate on that? I’ve never checked one of these

 

[press1280]

Ok that makes sense. I’ll check it out

 

[press1280]

On the chart look at the far right side and it lists pin numbers on the PLL chip and if they will be in a high or low state for each channel. A low state (0) would be near zero volts and I assume a high state (1) would be near 5v or at least above 3v. This will tell you if the channel selector switch is providing the right info to the chip and if someone might have done a mod to change the frequency range.

Checked a few channels and they are consistent with the truth chart, showing about 6 volts where there’s “1” showing on the chart.

 

[KB4MSZ]

Take a look at Pin 9 on IC1 and tell us what you see.

 

[press1280]

No volts there, pin 18 is always 6 volts