MSF 5000 TX VCO QUESTION

[BigJim]

I have an MSF5000 C73CXB VHF Range 2 that the TX VCO won't lock. Strange thing because when I first programmed it, it was fine. No problems at all.

It will lock when you have the locking unit for tuning and transport engaged. VCO stays locked and transmits fine and right on frequency. Not a high enough reading on the DMP though.. Needs tweaked.

Switch the transport lock back to operate position, slide the tray in and NO VCO LOCK LIGHT..

My main question, how deep in and what type of head is on the adjuster? None of the tuning tools I have will even touch anything inside the tuning hole.. Have several plastic tuning screwdrivers and hex units I have collected over the years. None long enough.. How deep in there is that tuning slug or whatever it is?

As you can tell I haven't worked on one of these before..

Thanks to all!!

BJ

[Doug]

The VCO's in a VHF station are non-adjustable. They either lock or fail. From what you are describing my best guess would be a poor connection on the VCO itself. Check and clean the RCA connector or the 4 wire connector coming in on top. While your in there make sure the uniboard is firmly in place.
I haven't played with a VHF station in a while so I don't remember if you can remove the end caps from the VCO's them selves or not but if they are it wouldn't be a bad idea to clean up the insides. UHF stations were prone to "whiskers" on the inside which creates a lot of havoc like I say not doing a vhf for a while it's a little foggy to me
Doug

[BigJim]

Thank you very much. Haven't had that top cover off yet. I'm not overly impressed with the way the service manual describes this, but then again I'm not a tech either. Beginning to feel I know just enough to get in trouble, but it's at that point I haul stuff to a friend of mine that IS a tech and owns his own shop..

Thanks again, BJ

[BigJim]

Removed the top cover and cleaned the connectors on the VCO. The VCO itself seems to be sealed except for the center hole on the RCA plug. I didn't poke anything in there to find out.

Here's the strange part. If I ground the VCO to the outer housing that's when it will lock. So it was just grounding through the locking cam.

Could there be an internal ground that has failed??

Any more ideas?? Wires all look excellent.

Thanks

[kcbooboo]

The VCOs should get ground via the black wire going to each one. If you flip the Uniboard up, you can follow the cable and make sure it's OK.

Also should get ground via the shield on the coax with the RCA plug. The other end is soldered to the Uniboard. The ground connection can fail if the cable is bent sharply.

The VCOs float on springs. They probably don't depend on those for a ground connection. If you manually push the VCO down about 1/4 inch until it bottoms out, you'll be doing just what the locking cam does.

Bob M.

[BigJim]

These VCOs sit in a rectangular plastic ring about 1/32 thick by a 1/4 wide. 4 round pegs at the corners keep the VCO from moving around very much and prevent grounding to the case. They are not soft or spoungy, no cushion. There are no springs.

I did find a bad ground in the connector from the VCO to the uniboard..(brown connector on multi-wire cable running to uniboard) Black wire just like you stated. Fixed that and set the board back down. That board seems like it has a loose fit on it's connectors to the tray..

Powered it up and now I have a ton of error codes coming up. I'll update as I go, please feel free to add any advice or comments..

UPDATE Tried to read it to check programming and now get "fail to communicate with TTRC board check connectors". Not having a real run of luck these days!!

Thanks, BJ

[BigJim]

Disabled TTRC as I don't need the functions it provides..

That took care of the errors for it.. Now I'm getting

E40: RX_Loop_Ctrl line not changing status--The RX1 loop signal is not toggling as expected, indicating a bad receive synthesizer.. Replace uniboard.

E41: TX_Loop_Ctrl line not changing status--The TX Loop signal is not toggling as expected, indicating a bad transmitter synthesizer..Replace uniboard.

E47: Transmit Synthesizer failed to lock. Recent Freq change or bad VCO--Reprogram SSCB or retune TX VCO.

E49: RX Synthesizer failed to lock after 3 program attempts. Recent Freq change or bad VCO--Reprogram SSCB or retune TX VCO.. Yes the manual says TX VCO..

HELP HELP, I can't believe this thing can go all to crap at once..

Thanks, BJ

[kcbooboo]

Make sure the Uniboard is firmly and properly back in place. It sounds like some of the signals just aren't making it. Remove it and reinsert it carefully. Make sure no cables are caught, crimped, or crushed. Then put the RF Tray cover back on.

I've only worked on UHF and 896 MHz stations, and in those the VCOs are supported on springs. Maybe your VHF station is real new or real old if it doesn't have them, or perhaps Motorola redesigned the support system.

Oh, regarding "I can't believe this thing can go all to crap at once..." believe it! When these stations work, they work really well. When they go sour, you have to really know how to fix things.

Bob M.

[BigJim]

Anybody have a uniboard for sale? Looking for one for a C73CXB7106BT MSF 5000. Range 2

Trouble started after I lifted the uniboard to work on the bad connector.. Just seems as if that board slids onto the RF tray connectors too easily.. You can just drop it on and it will fall into place.. You sure don't need to push it down.

It's like the man said there are bad connections somewhere, the correct signals just aren't making it..

This uniboard probably will be wrecked when I am done but I'm not giving up quite yet..

If anyone has worked on these or has a suggestion please chime in..

Thanks to all!!

BJ

[BigJim]

Cleaned all connectors on uniboard one last time. Re-installed and still had errors.. Was pressing with a rubber wand trying to find a bad solder trace or just anything.. Pressing harder than should be done I saw the VCO lights flicker.. More pressing and the board snapped down about a 1/32 inch on the right end..Don't know why I missed it before, I had that board loose many times while cleaning.

The lights are on and the thing is working perfectly.. Big Moto God must have been smiling down on me today...

I know the truth, it's called DUMB LUCK!!

Anyway it's up and running. Thanks to all who read and replied!! This is a great forum..

BJ

[w7gk]

Use a 3/16" Allen wrench to adjust the Rx and Tx VCO slugs.