2950 alignment issue

[711]

Got a fixer upper and during the PLL alignment I cannot tune VC2 to pull in 17.305mhz. Best I can do is 17.30430mhz. What that equates to so far is my RX being roughly one channel too high. On 27.2050 on the radio , I can hear my signal generator at 27.2150 however I can transmit on frequency on 27.2050. Measuring IC14 pin 3 , the best I can adjust for is 10.23940 MHz . Am I wrong to think my X2 10.240 crystal is bad.

 

[Low_Boy]

That radio does have a offset so you can transmit on one channel and receive on the other.

 

[nomadradio]

It also has a receive-only clarifier. Has to be set at 12 o'clock when setting the receiver on frequency. I'll look up the trimpot that sets the transmit frequency equal to the 12 o'clock clarifier frequency soon as I pull up the schemo.

73

 

[Handy Andy]

When you mention Fixer Upper, my sympathies immediately go out to you. Now you have to figure out what was done, undo it, redo the radio to stock, recreate the original - if there was a problem - now fix that...

Reminds me of a charge chart...

Something about having to double charge the customer for having to Undo their work, redo the work properly to recreate the original problem the customer tried to fix to solve the problem that brought you in (the customer) in the first place...

IN light of the suggestions posted in this thread already above - a 2950 uses power from the main board to reference the varactor - so if someone did some work to the main PCB - the problem lies there - and quite possibly they did "jumper" a resistor. Being nearly 20kHz off the original channel sounds like an offset program or the main PCB had some work done to it to let some one hear another channel but talk on the one displayed. IF you can manually reset the 2950 and the problem doesn't go away then the offset programming was not the issue.

The Clarifier can track RX separately - but again - someone may have tried to tie the Clarifier so it can track RX and TX at the same time...

J118 - by PLL - and D69 - TX side of the Clarifier...


See above...Then look for fresh work - it is not often a resistor on the CPU board that does all the display work - goes bad - but it can - but make sure the work that can get at easily done or accessed is correct to stock.

The RIT or RX adj./Clarifier, the range the knob can go in frequency adjust is quite extensive so look for any conversions they may have tried and found out it failed - this would make the radio work like it's in an offset - and if they didn't return it back correctly - just be thankful you got this far and didn't wind up with a toasted CPU card left behind for your efforts to rebuild. There may be a header with a wire cut or wires soldered to the foil side of the board that you know is not right for it to be there. See above...

So I'm thinking the Receive Tuning pot may be dead - trace those wires back to the main PCB and see if there is work done to it. Voltage should be there on all leads of that pot and the "ground - power and variable" are all traced back to the main PCB - the CPU sends the main PCB a reference signal - but it needs communication from the main PCB to know what it's doing with it.

:+> Andy <+:

​

 

[711]

Went to a hamfest yesterday and didnt get a chance to get to look at the board much. What I do recall was a few things that were odd. Seems like the CPU board looks more like a DX model, where as the battery is nounted below on a shiny chrome plate and the connectors are tightly bunched together much like as seen in the DX service manual. When I first tried to align X2 portion, the highest I could get the frequency was 17.304 mhz as stated above, I tried turn the clarifier in an attempt to try to bring it closer to no avail. seem like it had little to no effect, clarifier locked? I seen no evidence of a clarifier mod. I did unsolder the X2 crystal to see if there was any damage and it was fine so I reinstalled it. I read Nomads post on the cheap Galaxy fix but there doesnt seem to be a cap to short out like the 99V he mentioned. I also saw a suggestion to replace FL1 , so I swapped a known good and the same result. My final attempt was to try to add caps in parallel to VC2 and the frequency dropped , so adding went the wrong way. This again was before my first post. One last observation was the rotary channel knob when spun was not sequential, the frequency went all over the place when spun. However the up and down buttons functioned properly. I'll try to take a closer look at the CPU board for any possible mods there. Almost seems like a backwards connector and or a stuck 10Kc button if this thing had one.

 

[Handy Andy]

Ok, that Takes us a little further.

Got a Main PCB board number?

You said DX, it narrows it down - and now people who read this for future reference - it may help those that are trying to help the poster, if and what - they are up against - any identification that narrows down the type of radio not just a "2950" or 99VHP - but board number - as you go thru this you'll see why.

Ok, the DX comes in several flavors - with MOSFET's served insides; so you know...

One board uses the TA7222P chip which has it's own Mute pin...
Another board uses the TA7003 5 pin chip with it's own pinout issues...
Another board also uses MOSFET...

So, on we go...

Look for D63, its' the TX trimmer from the main PCB...that goes to the CPU board.

Does your radios' front panel look like this?


They again, use this setup - main PCB communicates to the CPU - the CPU then updates display and tells PLL to SHIFT in the direction you rotate the VFO knob..but main determination for frequency is still thru V8 TX adj, and FINE Clarifier trim on front panel for RX - all branched thru J28 and two steering diodes, D63 and D41 - with VR 8 "adjusting" for TX tracking side.



Again, back to the main PCB - locate the Fine control header J28 - that is the RX side of the VCO fine tune adjust trimmer branch that goes to VCO and Varactor diode.

IF they did any mods they may have damaged the Clarifier Pot, TX Trim VR 8 Pot or J28 - look for and correct the mods, any work really including up at the Clarifier board behind the front panel - back to stock to regain center and proper Clarifier control.

IF they did what I think they did, then this section right next to it - is damaged or potential failure in it somewhere..if you cannote restore the Clarifier after getting J28 working right...again - it acts like you "lost your RX control" because the VCO is running off the VFO display - which isn't right, but it functions because the CPU seems to be still working - the VCO from the main PCB to balance it, may be out - your side, is not working.

From Rick Jackson and Euro Radio Co...CB Tricks...


Remember too, that if a mod was done and they APPLIED more than 8 volts - to this section - you may have a cascaded failure of the VCO and Varactor area by VC2 - right next to this section. Meaning they killed the ENTIRE thing and you're running straight off the VFO front knob. It may explain your "Offset".

The above "schematic snippet" is from CB Tricks and Euro Radio - and note the PLL is similar to the 145106 but now...its SERIAL DATA programmed - so it no longer has parallel pin programming like BCD - it's CPU controlled programming now - so again, the main PCB communicates to the CPU and CPU controls the PLL and you handle the OFFSET VCO - as shown above.

:+> Andy <+:

EDIT: Revised SMD

 

[711]

Andy,
Im still at work but the CPU board looks like a DX model as compared to whats on CBtricks but the main PCB is a normal through board 2950 board

 

[Handy Andy]

Well, at least it still has discretes' means that it built during the times of various stages of transition from one mounting (thru-hole) into the modern (SMD) - so use what you can from above, we'll be here to help if you need.

Just ask!

:+> Andy <+:

 

[Low_Boy]

A lot of the older 2950's have encoders that have went bad.

 

[Handy Andy]

That's true!

In many ways were shooting in the dark - going on recent events of relevance in our lives to help the one In need.

It is my hope that I'm even close to offering tangible advice.

Hey, if its' any consolation, my XYL and I went out to eat at a local restaurant - haven't done it in years - felt good - so yes, I do have a life outside the keyboard - you just don't see the balls of fun I have over here (looks at the table - grocery list and receipts for various consumables and perishables, along with coasters and a tape measure - just don't ask...

Where were we???

Now many will see why the revisions they (RCI) went thru - are what thy are - note that the Thru-hole boards, the first revisions were pretty simple and had a lot of "individual parts" that seemed to have no purpose - except maybe to filter out an artifact here or there - or even offer a roger beep "enhancement" or tonal effect.

Some, had applied noise abatement and receiver performance enhancements - like using varactor diodes reverse biased, at key areas of RF or Audio feeds. This added complexity but kept the hash noises and switch clicking down for areas that were sensitive to the noises they can inject from noisy clocks and CPU lines.

They even used those transistor toggles to operate like switches to turn sections of the radio on or off, eliminated the front panel leaks and noise injection issues - by buffering - removing the analog switch and all it's faults and inherent noise and voltage drops it gets when its used as it ages - replaced with a switch that just needs the CPU to send a 5 v high or low and the radio keeps all its' noise to itself and shielded (loose term) from the noisy realm it's operated in...

Galaxy and RCI were hand-in-hand a long time before the rest of the world noticed...at least before the "keep memory alive" batteries quit...

As the years progressed they got really aggressive into serial PLL chips - the ones that use a CPU to clock data in for programming the PLLs' "Go-To" - Uniden (687 787 as well as the new Bearcat line) does this as well as Midland (77-285 - 5001 even) some, like Midland, use a single CPU / PLL but remotely store the data - so part of the "Boot" process is to clock the data in to the CPU - there are pins on the chip that tell it to execute a function once enabled and in many instances, that's how it "hides" extra channels and features - they may not toggle on that particular board but ones that have the external support - obtain it - Noise Blanker, AGC tracking even Channel Plans for various regions and countries - not just USA.

But, the redeeming factor that makes RCI appealing, is their platform standard they've kept through these revisions. At least you have the display, the main PCB and the VCO tracking function like the RCI was noted, remembered for. So their Masthead was there original Clear Channel 2900 an AR-3500 brothers of different Mothers. Not unlike Galaxy and Cybernet and Uniden - who where those guys - really?

Sure a lot of people would say they're junk, and perhaps they may have a point or two and several examples for each. But one thing that cannot be ignored is for their approach to the hobby and the enthusiast - give them what they want - they'll learn how to shut off what they don't want - sooner or later.

So to learn, let them in then - we will be here to help. At least their platform (RCIs') of how they make a radio work, has not changed yet - I hope.

:+> Andy <+: