Looking for Rapco (Pendulum) 2804B GPS Clock w/OCXO "CLIP"

[Uky]

Greetings.

Having picked up a RAPCO (Pendulum) 2804B GPS-clock at a flea market, I posted a message searching for a manual
on the time-nuts mailing list. A user manual was kindly provided and it did help in starting the troubleshooting
procedure.

I am however stuck in trying to figure out why the frequency locking of the built-in OCXO does not work.

The control loop circuitry adresses an AD7846 - 16Bit Voltage Output DAC that controls the OCXO.

After indicating "Frequency Lock", the DAC output voltage goes from a value that sets the OCXO
close to 10 MHz, but then latches up and saturates at "99.9%" of the tuning range. This puts
the OCXO at 10.000.002 MHz...

I am presently investigating if the problem is the 7846 (Datasheet available) but if this
IC is good I don't think I can go any further.

Rapco was purchased by Orolia and then by Safran. The 2804 is obsolete since a long time
ago. I dont think approaching Safran would be successful. If anyone has more information
that the user manual, I would be grateful.

 

[Uky]

... I think the request for a service manual can be withdrawn.

There are two pieces of ALTERA CPLD's where at least one of them outputs data to the DAC.
Regardless of having the DAC socket populated or not, testing the DB0...15. The lower bits are "alive" but the upper dead.
Either stuck logic high or low or somewhere in between.

Will salvage some parts. The rest -> scrap.