Hi Ronan,
The MS5351 datasheet shows an absolute maximum Vdd rating of 3.8V. I’ve measured the voltage across D109 under high-current conditions and have seen it consistently exceed 3.8V and even exceed 4V at 100 mA. The primary failure mode of D109 occurs if the PWM_3V3 input gets stuck high or if the duty cycle becomes too large. Based on the measured results across 14 boards, I suspect that the failure of this 3.6V zener correlates strongly with a failure of the MS5351.
Tony AC9QY
On Sun, Sep 8, 2024 at 11:28?AM Ronan Cantwell via <ronancantwell=
[email protected]> wrote:
Ok. I've fitted new bs170's and rewound the RWTS transformer. Further testing shows no sign of any clock signals at all from the 5351 which would explain the complete lack of RX. It may also explain why two of the bs170's were getting toasty on key-down. I had initially suspected a short in the output transformer but, in hindsight, I would have been able to detect even a small amount of RF if that had been the case.
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Could the failure of the 5351 have been caused by the initial fault with the 3.6v zener on the 3.3V board? If so, are there other parts likely to have also succumbed?
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I'm not sure how much time I can justify putting into this but I would like to get it back on its little feet again. Any suggestions, pointers or advice would be welcomed at this point.
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Cheers,
Ronan?
MM0IVR?
