D19 fault (MS2 v3.0)

[niaugi]

Hi,

this morning uploaded new map and wanted to start an engine, but suddenly no connection with MS and everything is dead.
so started to investigate:
cpu 1&2 PINS are almost shorted, U5 is extremely hot, voltages are low
looking at the MS2 v3.0 power scheme i found D19 when disconnected all voltages normalizes and MS is working (with stim)
so my question is, can MS run without D19?
or if not, why did it happen? should i replace with a diode which is stronger/better one? what is D19 for?

[niaugi]

ok, found nice troubleshoot:
http://www.megamanual.com/ms2/V3trouble.htm
14 b) explains all i wanted to know
will go for 6.2 Volt Zener diode then, hope it helps.
also i found Stabilitron 1.3W 6.2V, are they good as alternative for zender diode?

is there a source of voltage spikes to prevent D19 from burning?

[Six_Shooter]

I would replace it with another 5.6V Zener diode. The way it's being used in circuit is to clamp the voltage so that it goes no higher than 5.6V as protection for downstream devices that are designed to work on 5V.

Check the output of U5 and the ground to U5 to make sure that it is putting out 5V ±0.1V from pin 3. If the ground for whatever reason is poor, the voltage could spike.

Also check D9 to make sure it's still acting like a diode, if this is damaged and acts like a short, the voltage on the output side of U5 will be at or close to the input voltage.