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I have recently purchased a Motorola Nucleus UHSO module and have tried everything I know to do in order to get it to work in a Quantar or a Quantro station. The module is Motorola Part # TRN7812C. This reference module has a 5 MHz oven crystal in it as well as a GPS receiver. The receiver puts out the 1 pps. I have tried to get the module to work with and without the GPS antenna hooked up to no avail. I do have 5 VDC on the antenna connector so I think it is working properly
In the CPS I have selected the frequency reference source as internal UHSO, verified the configuration and let the station go through a warm up time after writing the codeplug to the station. I normally expect about 10 minutes for one of these to lock. This one never locks. In the station status screen in CPS the UHSO shows failed and when you look at it in the metering screen it shows inactive. I took my external frequency counter and sniffed J30 on the backplane. I found 5.000001 MHz output on the BNC connector. In the metering screen the steering voltage etc all are within specs. It just shows the 5 MHZ as "inactive".I could understand for some reason the GPS receiver not putting out 1pps and that preventing the UHSO from outputting 5 MHz to the backplane but from all I am seeing that simply is not the case.
After much time spent in the schematics in the service manual and time looking for signals on the back plane I could not figure out why this would not work. I ended up taking the stable 5 MHz reference present on J30 on the back plane and routing it up to the 5 MHz input on the front of the SCM. I then reprogrammed the station to External 5 MHz reference. After a quick reboot and oscillator warm up time the station is happy. I can not explain why this reference will not work in the Quantar or Quantro on my test bench. Two different stations one on VHF and one on UHF and they both had the same issue. When you remove the 5 MHz reference cable from the front of the SCM the station immediately goes into RX fail synthesizer unlock etc just as it should. After hooking it back up the station locks and starts working. I know this is really a work around and not really a fix but for my ham repeater application this will suffice.
I have attached a photo of the frequency counter. I put a BNC T on the front of the station and hooked the frequency counter inline.
I would assume the UHSO module also communicates with the Quantar/Quantro units via it's backplane edge connector, but since it's a Nucleus module, the Quantar/Quantro firmware cannot recognize it's existence.
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I kinda had that idea as well but can't confirm it. I wish I had a Nucleus service manual so I could look at the pins on the back plane to see any variations. I don't want to have to reinvent the wheel so to speak by reverse engineering everything. I will keep an eye out for a service manual for a Nucleus to appear on that famous auction site.
I don't think any Nucleus service manuals exist. From what I've seen, the backplane is quite similar to the Quantar. I do know there are about a dozen missing parts on the 900 MHz Nuke exciter compared to the Quantar, and it's all in the REF MOD circuit, which is necessary for proper low-frequency (i.e. PL/DPL) modulation. You don't need that circuit for paging tones or FSK. The rest should be pretty close. I too would have expected the UHSO to work.
Motorola sold the Nuke product line to some company in England. Prior to that repairs consisted of module swaps only.
