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Post by sfi355 aka Billy Bob on Sept 8, 2023 11:31:24 GMT -5
Hello to all. I acquire a Tristar 747 with no RX/TX. My question is on the PLL 02AG chip the voltage going into the chip is 5.39 volts. On Pin 4 I see 5.01 volts and on Pin 6 which is the LD I am only seeing .67 of a volt. My question is should there be 5 volts on pin 6? Now I disconnected the pin 6 from the board and the voltage is still at .67 of a volt. Does this mean the PLL is no good? Thanks for your time. 73
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Sandbagger
Administrator/The Boss 
Posts: 6,250 
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Post by Sandbagger on Sept 8, 2023 17:48:43 GMT -5
Hello to all. I acquire a Tristar 747 with no RX/TX. My question is on the PLL 02AG chip the voltage going into the chip is 5.39 volts. On Pin 4 I see 5.01 volts and on Pin 6 which is the LD I am only seeing .67 of a volt. My question is should there be 5 volts on pin 6? Now I disconnected the pin 6 from the board and the voltage is still at .67 of a volt. Does this mean the PLL is no good? Thanks for your time. 73 Pin 6 of the 02A PLL is the Lock Detector output. When the system is in phase lock, that pin will go to a logic hi (5V). If you are only seeing .67V, then that means that the PLL is in an unlocked condition, so you won't have TX or RX, at least not on any frequency that you want. As to what causes this, well, there are a number of things. While the 02A chip itself COULD be bad, it is not known to fail very often. I'm not familiar with the TriStar radio. Is this an SSB chassis, or just AM? The Cybernet SSB chassis has a VCO module which is known to fail. Other than that, there are mixer crystals, the reference crystal, and even a misalignment of the VCO which can contribute to an unlock condition. It's not something that can be systematically troubleshot remotely. You can check for the presence of the required oscillators with a scope. Hopefully you have a good schematic to work from. You can also check Pin 5, which is the VCO drive. It should be in the 2V to 4V range. If it is showing 5V, that means that the VCO is low (or missing) in frequency. If it is less than 1V, that means that the VCO is too high in frequency. |
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Post by 2600 on Sept 9, 2023 22:37:05 GMT -5
Don't have a schematic of that one handy, but I do know that the 10.24 MHz crystal has to be running for the PLL to lock properly.
73
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