Received two of the subject units, one built in 96 and one in 97. The dates are the first two numbers in the serial number.
Took the 96 apart and learned that the LPRO-101 is not physically connected to the main board, except through a pin connector. When the unit is turned upside down, you can see a pattern of 6 screws in two rows of three. These secure the LPRO. The rest of the screws hold the main board. Do not turn the unit upside down but stand it on its rear fins as you remove the screws. This keeps the LPRO from dropping away and bending the pins. The LPRO has a thermal plate that provides good conductivity to the case, so it can dissipate about 15 watts. There is no thermal goo between the plate and the box, but the plate may be stuck to the box. Put a screw in a hole and push on it to release the LPRO. Then, if you have removed the 10 screws that hold the panel to the box, it should all lift out easily, with the LPRO hanging by its connector. I'd recommend laying the box down in its normal position and sliding the innards out horizontally. Imagine my surprise when what I'd learned didn't work on the 97 box. That assembly has a clamp that holds the LPRO in place, so pushing on a screw doesn't work. There are four screws on the back, between the fins. Loosen them to loosen the clamp, but don't remove them. Reassembled both - you don't want to run the LPRO without a heat sink. The 97 unit drew 1.4 amps at 24 VDC at startup. The NO GPS and Fault lights were lit. The current dropped to .7 amp but the Fault light was still lit. Got 10 MHz at the J1 test point but nothing at the 10 MHz output. Went away for an hour, came back to find the ON light, got 10 MHz at J2, didn't check 15 MHz. The 96 unit had the same behavior, but the 10 MHz was more accurate. The box got quite warm, but you could keep your hand on it. (How's that for quantitative?) I have two Z3801s and two Racal-Dana model 1992 counters set to Phase A-B. One counter has been measuring a 4040 cesium box against one of the GPS receivers. The other counter measures the phase difference between the Z3801s. With the 96 unit in place of the 4040, phase rotation was 220 degrees in 20 minutes. The GPS comparison doesn't rotate, but varies between 50 and 70 degrees. I consider that an indication that the receivers are OK. The holdover accuracy varies between 0.5 and 5 microseconds, depending on when the crystal last cracked. If I did the math right, a 360 rotation will take 2000 seconds. This means the LPRO is about 5x10E-11 off from GPS, no? Two other questions: What is the BITE pin on the LPRO? Some Built-In Test? What is the protocol for the data at J6? Can it be the same as the Z3801? Bill Hawkins _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
