Most 8566/68s show the Oven and REF Unlock initially connected to power.
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On Mar 8, 2022, at 13:19, Bruce <bruce@...> wrote:
OK -
Good information. The fact that you see the REF UNLOCK suggests that the 10MHz freq ref may need adjustment. This will mask any mis adjustment of the 100 MH REF OSC.
This suggests that ref problem COULD be the problem with the YTO but that there are MORE LIKELY other issues. Let me review the 8566 diagrams and come up with a set of steps to better identify the issue.
Two things to try:
1) Measure the LO output at the front panel - be careful, it could be as much as +8 dBm
2) Measure the voltage at the 100 MHz oscillator (A7A2) control voltage (volt meter and scope)- this is available at the test point on the top of A7A2 (Right next to the "pull handle") - you can measure the 100 MHz without pulling the A7A2 module - signal is available at J3 on the top panel - removing this cable will mess up the 10/20 PLLs, but you don't care in this case.
The voltage at the test point should be a (relatively ) stable DC voltage (there may be some noise which should be small compared to the DC level). The expected voltage at this test point is -8V Let me know what you measure.
The power at the LO output should be (roughly) 4 - 8 dBm. The power at J3 should be (roughly) 0 dBm If possible, it would also be a good idea to check the power levels at J1 (-10 dBm 400 MHz) and J2 (0 dBm at 100 MHz).
Question - Which of the green LEDs is not lit (on which module)? If the measurements above ar reasonable, we whoould next look at that module's PLL. No point in chasing the YTO unlock, till all the other PLLs are locked.
Cheers!
Bruce
Also, can you measure the power at the LO
Quoting Jinxie <paul666@...>:
Bruce, further up the thread you asked what error messages I'm seeing. I have just re-checked and my earlier comment was correct. At switch on, I get these flashing:
Oven
REF Unlock
YTO Unlock
Battery
After 6-7 minutes, the Oven and REF Unlock errors disappear. The YTO Unlock and Battery ones persist.
I would like to check for the presence of the 100Mhz reference signal, but there doesn't seem to be any facility for doing so without removing the board with some form of extender. In any case, both the 500kHz signal and the 500kHz divided signal are so catastrophically crippled that I believe the most likely explanation is intermittent power failure in that section. I don't see how an issue with the 100MHz reference oscillator would produce the trace I'm seeing. I know it's extremely difficult for you and everyone else to visualize the trace from my description, but it's not something a single picture can adequately convey and I can't post video clips of my scope's screen here, unfortunately.
