I had one of these drivers a while ago, and I'm pretty certain the unlock LED was fully extinguished when in lock.Shedbuilt wrote: ↑Tue May 23, 2023 9:03 amI'm not sure on this, but I think it may be normal for the unlock LED to stay partially on. Are you (frequency tuning wise), in the middle of the oscillator's lock range ? I tend to doubt a leaky LED driver transistor, especially as the LED brightness is varying. I'm more inclined to think that the transistor is being held partially on.MiXiN wrote: ↑Mon May 22, 2023 4:23 amThanks for the reply, Albert.Albert H wrote: ↑Sun May 21, 2023 4:56 pm Hollings' version of the PLL has a missing "balance" transistor. There should be four transistors in the oscillator stage - the two that generate the ½f signals and two buffers - one of which feeds the PLL and the other just provides a balancing load to ensure that the two signals are exactly equal, thereby giving the cleanest possible signal at the output frequency when combined. The PLL Pro III uses a pair of FETs for the buffers, earlier versions use BF199s (or even BF494s on the really early ones).
Hollings didn't understand the operation of the oscillator, and how essential accurate balance actually is. If the balance is degraded, lots of ½f breaks through, and there can also be an amount of 1½f as well.....
Upon inspection, the Oscillator stage in my PLL3 only has 3 Transistors like the version above, so it's an Hollings variant.
With regards the PLL unlock LED not fully extinguishing even when the board is in lock, where do you think I should start looking for the fault? I'm thinking a leaky collector/emitter junction on the Transistor that drives it, but apart from that I'm not sure where to look?
When in lock, the PLL lock LED is fully lit, and the PLL unlock LED is around 50-60% brightness simultaneously.
Operation appears fine, but it's just an annoyance.
I'm doing this at around 100Mhz, so I'm roughly in the middle.
I'll have to get a voltmeter on the base of the unlock LED Transistor to see if it's partially biased, hence the LED being lit.