RCI-2950 non dx Frequency problem

[Alabama Trainman]

I have a 1st Gen. 2950 that transmits and receives...but not on frequency.
In tx mode it transmits 23.154MHz no matter what channel your on. Im thinking the CPU is ok because the display reads correctly. My gut feeling says it may be something with the binary code from the encoder...but just wanted some opinions about something I can check. Radio was working just fine and then it cut out and started doing what it's doing. Thanks in advance

 

[BayouRadioAmplifier]

I would check out the PLL circuit. check the VCO to be on a certain
frequency when radio is set to 28,000 kHz. there is a procedure in
CB Tricks.

 

[999]

I would check out the PLL circuit. check the VCO to be on a certain
frequency when radio is set to 28,000 kHz. there is a procedure in
CB Tricks.

This is what I was able to find.

 

[nomadradio]

First gen?

As in, has a coin cell soldered to the rear CPU circuit board?

That radio is pushing 30 years. A PLL problem could also have one or more electrolytic capacitors at its root.

Or a handful of cracked tuning slugs from a previous episode of tweakeritis.

That PLL does quirky, sketchy stuff if even one of the tuning coils in that part of the radio is not peaked on the money. This radio has two phase-locked-loop circuits, locked together. This means that there are two separate circuits that can each become "out of lock" even when the other one is adjusted perfectly okay.

The procedure above usually sorts it out. I always tune in the two 10.24 MHz oscillators separately to make sure each is running smoothly and on the right frequency. A ham radio that can tune in to 10.24 MHz is pretty handy. Unless you have a communications service monitor to make the same check.

73

 

[Alabama Trainman]

Well, I had both VCO voltages...the radio was transmitting and receiving. The only issue I was having was the radio was transmitting on 23MHz and not on 27MHz. After more testing I found the proper mixing frequencies going to the tx mixer were not right.
Now I have lost my 2v on J13.
I do have 1.2v on Pin 3 of IC 7
I do have 10.695MHz on D45 in TX.
I do have 10.240MHz on Pin 1 of IC 11.
I also changed C107 and put in a 100pf cap.
Need help trying to get my 2v back on J13. Thanks.

 

[nomadradio]

My best guess is the L24/L25 combo. They interact, and the "adjust for best waveform" is sketchy at best.

But that's really what you need to do.

Bear in mind that if what's coming out of the radio really is 23 MHz, that L17 is set way wrong.

Not a common fault for me.

73

 

[Alabama Trainman]

My best guess is the L24/L25 combo. They interact, and the "adjust for best waveform" is sketchy at best.

But that's really what you need to do.

Bear in mind that if what's coming out of the radio really is 23 MHz, that L17 is set way wrong.

Not a common fault for me.

73

I will try that but first I need to fix the issue with VCO1. The radio uses 3 mixers (TA7310P). I'm going to check them out today. I need to get that 2v back on J13 before the radio will even transmit. Thank you for your input and I will post an update after further testing.