OLG1 repair (maybe)

 

I have an OLG1 that stopped indicating the 1PPS signal. It gave me quite a few years of non-stop service so no complaints. 

I tested the board today. My hope was that the LM317 had given up (more on that in a bit).

LED's 
Red Power On
Yellow Data Blinking
Green 1 PPS Off

I tested the 74ACT08 (quad two input AND gate). I pulled out my logic probe for that (and the crowd said oooh... ahhhh) :D

Pins 8, 9, 10 (TxD from the RF module) and  Pins 11, 12, 13 (also TxD but used to flash the yellow LED) were cycling as they should be. 

The 1 PPS signal was missing from pins 1,2 (from the RF Module) and therefore pin 3, which is also pin 4 and pin 5, which turns on pin 6, which turns on the green 1 PPS LED

The RF module is unobtanium (from new stock) so I hopefully tested the LM317. Based on the resistor values on the schematic the output voltage of the LM317 should be 3.44V. The design section of the manual says 3.3V. It's actually 2.2 volts. Is the output low because the LM317 output is being pulled down by a faulty RF module? Have the resistors drifted off that far? Doubtful. Bad LM317? That's an easy and cheap fix. I used the patch antenna when I built it. The GPS I replaced this one with is sitting next to it happily pulsing away so I don't think it's an issue with the signal strength of the satellites.   

Is there something that I can check other than the 1PPS signal from the RF module?

--
73
NE5U

Mike

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