Hi every body, I've a problem with a card with Aduc 812bs micrcontrolor, pins (20-21;47-48) have (27ohm only) the rectifier (Lm7805) is boiling, I know that ADuc 812 is protected from short circuit ,normally how is the magnitude of the resistance between pins 20-21 or 47-48? Is The microcontrolor out of service?
N.b all other components are verified: capacitors ,resistors, diodes...
The ADU812 is 8051 based I believe so please select C51 instead of NONE.
Is the ADC812 overly hot? If not I doubt the resistor values are too low. What are these pins driving? What other loads do you have on the +5V?
If the LM7805 is hot and the ADU812 is not hot then you should look at the output capacitors of the LM7805. Usually there are several capacitors on the output with one being either a tantalum or an Alum electrolitic.
These can be installed backwards and the system will almost work until either the capacitors or the LM7805 gives up it's magic puff of smoke.
Break the circuit down. Lift a pin on the microcontroller or cut output traces from the LM7805. Small cuts can be easily repaired but burned devices cannot be repaired just replaced.
Good luck!
Bradford
hello, thank's for your reply..
I've almost lift all the capasitors also the other loads ( integrated Circuits !!!!! EEprom with 20pins , the only the Aduc is not lifted , I've cutted the pin (+5v) but the problem still the same. because the microcontroller has other pin uses +5v , it's hard to cut several traces; the circuit will be a rubbich (excuse me). the only hot component is the 7805 !!!!!!
not yet solved :-(