Just leaving this here for anyone fault finding
Just dealt with my second ?MS5351M 'subtle failure' in a couple of years
First was in a QCX +TCXO where after 20 minutes or so running the Transmitted WSPR tone degraded into wide band noise that amazingly did still include enough of the right signal to get a WSPR report and show the usual power output to the antenna.? ?Several people around the world helpfully pointed the problem out as their spectrum displays were in a mess and I very quickly shut it down ......? ?
A spray of cooler on the 5351 paused the problem.? Fixed by replacing the MS5351.
Second just now was in my U3S with receiver option (SI5351 board and QRP Labs TCXO) that was starting to emit random audio noise in receive at a high level once warmed up.? ? The CLK1? 56.3824 MHz Park /Receive LO carrier in this case was sniffed for but not recognisable on another receiver but a noise spectrum a few KHz wide was filling the vacancy.? ? A quick sense check of removing the BPF, swapping power supplies, moving/cleaning? interconnector pins, switches? etc did nothing, and the transmit signal (CLK0 14MHz remained pure).
Again cooling off the 5351 area restored operation for a few minutes . .? ? and replacing the 5351 oscillator board completely (for convenience) fixed it.? ?(Not dug deeper.? As the WSPR TX modulation was always fine and the regulator seemed happy enough I think its the 5351 again. . )
Both radios have been used in 24/7 beacon operation and their only faults so far in 10,000's of hours have been misbehaving MS5351's.? ?
So just leaving this note that they can fail subtly, don't assume part working means all working . .??
Bruce Akhurst