This is a setup which is in operation for the last 20 months without problems.

89c51rd2+DS1232+12MHz crystal. ALE feeding the Watchdog.

I know its not an ideal way to feed the puppy - but then I also don't need the watchdog functionality. So thought will get away with it.

The 5V switcher failed recently and it was replaced with an available LM317 linear stuff last week. After that the set up has become very unstable - the VFD display and the MCU just freeze on power ON and at times. Mostly it works fine. ( Even when it freezes, the Vcc is at 5.15 V )

It will be sometime before I can replace the 5V supply considering the site logistics. My question is why this should happen ? Is this some kind off C-Mos latch up ? O-Scope has not been very useful as once the MCU freezes all waveforms are stuck.

( I have searched the forum for similiar situations and generally the ALE feeding WD has been discussed as a method to adopt when the WD safety net is not really required )

Any tips / issues that come up to your minds?

Thanks

Raghu