i am going to repair a circuit which contains the sub c501 microcontroller and for this reason i wrote a simple assembly program. My program only sends a charakter on hyperterminal. The circuit comprises of from a MAX703 which controls the voltage level and connect the RAMs to the battery or on to the main,a lutch(74573) 2 static RAMs(62256), an EPROM(27c020), a RTC74243 and a EEPROM(I2C). In working circuits my program works fine.
My problem is that in some not working circuits i measure on the port2(High adress byte)a sort time pulse. This phenomen occurs at the same time on all port2 pins. Also sometimes, the output of the MAX703 is not 5V but 4V. Does anyone cope with such a problem? Could someone suggest what is going on?
Thank you for your replayies

i m sorry that i do not post the circuit, but this is on my work place. but i thing is a common circuit.