Need Tips or Help With 2950 Freq. Readout Adj.

[Wire Weasel]

Hey gang, trying to fix an older 2950 non-dx, orange display rig for a local friend. His grandson got ripped off in the buy. Paid $200. Hi/Low power settings were turned way down and the thing is way off frequency on all modes.

I've gone through the entire VCO-PLL alignment procedure outlined at cbtricks using a good freq. counter and high accuracy dc voltmeter. All settings at or near dead on the specs. Some points needed adjustment, others were already good.

L27 will change AM freq +/- a couple of kcs as should.

Rig talks great and sees normal+ power output

Prob is unit is about 7.0 kc's low of freq (to round it off) on all modes. Take Ch 19 for example. If you are actually TX/RX on 27.185 - display would have to be on 27.178 to be there.

There is no microprocessor reset button on this unit.

Any suggestions on how to match actual TX/RX freq to Freq display reading? Also frequency deviation is even greater when using CB channel readout mode.

Or stated another way, is there an adjustment to directly change the freq. readout. I haven't see one anywhere.

Thanks for any help

 

[Robb]

Had a similar problem with an orange faced 2950. Everybody touts these radios as something great. The truth is, that the CPU is no longer made for these early radios. If there is a problem with the CPU, you are stuck in trying to find a working one. The chances for that happening are getting slimmer every day. The new CPUs in the new radios won't work either. Chip @ Radio Shop Supply (factory authorized Ranger/USA warranty outlet) gave me the heads up with these radios. Contact him for further info if you must.

You can disconnect the battery and reset the memory. But this will have no effect on the freq display. The one I worked on was off exactly .1khz. Never could correct it despite alignment of the radio.

I also have a 2950 that the CPU is toast. Sometimes it works; and sometimes the display looks like it was written in the Klingon language . . .

 

[W3FAW]

Hi, have you fixed this thing yet? Let me know cause I have some ideas but I don't want to get into it if it's already fixed.

 

[Wire Weasel]

No but thanks, send back to out-of-state owner. Long gone. But feel free to post any tips for others to make future reference of !

 

[W3FAW]

Hi Wire Weasel, I have found that the most challenging part of aligning the PLL is the adjustment of L24 and L25. The book says: "adjust for best looking waveform on the scope" Well this is nearly impossible for me since I can never synch on the waveform. So I now use the trial and error method for achieving 17.305Mhz. But I don't start at 28.0000Mhz because if you achieve the 17.305Mhz, it doesn't necessarily lock at 29.0000 or any other step up. You may get it to lock at 17.305, but it will drift at higher frequencies. I start at the higher frequencies such as 31.0000Mhz and diddle with L24 & L25 until I lock at the equivalent PLL frequency ie. 31.0000 minus 10.695 is 20.305Mhz. So I dial the transceiver to 31.000 and try to lock in at 20.305. Once you achieve that lock in point, all of the lower frequencies should lock in as well. If you have any drifting, go back and do it again making sure that L24 & L25 are adjusted to the middle of the lock in range.

Everything else should be by the book. Be sure that when you adjust ANY frequency, that the clarifyer is EXACTLY at 12 o'clock.

This technique should have helped with your problem. I hope it helps others as well.

If anything in this doesn't make sense, let me know and I will try to elaborate. These instructions are only for those well experienced and properly equipped. Don't try this at home.

 

[Robb]

Hi Wire Weasel, I have found that the most challenging part of aligning the PLL is the adjustment of L24 and L25. The book says: "adjust for best looking waveform on the scope" Well this is nearly impossible for me since I can never synch on the waveform. So I now use the trial and error method for achieving 17.305Mhz. But I don't start at 28.0000Mhz because if you achieve the 17.305Mhz, it doesn't necessarily lock at 29.0000 or any other step up. You may get it to lock at 17.305, but it will drift at higher frequencies. I start at the higher frequencies such as 31.0000Mhz and diddle with L24 & L25 until I lock at the equivalent PLL frequency ie. 31.0000 minus 10.695 is 20.305Mhz. So I dial the transceiver to 31.000 and try to lock in at 20.305. Once you achieve that lock in point, all of the lower frequencies should lock in as well. If you have any drifting, go back and do it again making sure that L24 & L25 are adjusted to the middle of the lock in range.

Everything else should be by the book. Be sure that when you adjust ANY frequency, that the clarifyer is EXACTLY at 12 o'clock.

This technique should have helped with your problem. I hope it helps others as well.

If anything in this doesn't make sense, let me know and I will try to elaborate. These instructions are only for those well experienced and properly equipped. Don't try this at home.

If you could make it more clear, I can appreciate it. Any/all details you can add would be helpful. Most of my present experience is with Uniden-based chassis.

I do have the right gear (HP freq counter and signal generator, Tektronix 465 scope, etc) and have found the RCI 29xx radios a bit different/difficult to align.

Thanks!

 

[W3FAW]

Hi Robb, the only thing I can say is that it will all become clear when you have one on the bench and try to do a PLL alignment. It's not something you can talk about in theory, you have to have hands on. Regards, W3FAW