Forum,
Although not strictly related to antique radio, a lesson well learned FOR ALL OF US. Noted in one of my earlier posts, was an effort to repair '92 era Delco digitally tuned truck radio without any documents, and full of SMD's and microcontrollers. Sometimes it would play for 2 mins, then lock up and other times 15 mins before lock up. Tidbits of info gleaned from numerous web sites, led me to believe the only TI chip on the board (but with Delco #) was a TMS370 family microcontroller, so printed a data sheet for it, and the pinout appeared to agree. It was the primary component/culprit too. I had found all input lines correct, but the output driving a relay, which powers all radio functions failing. I had monitored the RESET pin on several occassions while operating, and found nothing unusual, but decided to cut/lift it (a non reset condition), still failed. I was able to trace the copper to a 4.7uf SMD cap across the 5V regulator, which applies the voltage to the reset pin as soon as batt power is plugged in, but didn't always occur at the reset pin. A short long story, the trace had a hairline break at the cap, which was solved with a leaded 4.7uf bridging the break. PERSISTENCE PAYS OFF. It has now played flawlessly for about 15 hours, and payday is just around the corner.
marv