If you’re having trouble picking up digital TV signals, you’re not alone. An electrical problem at Sutro Tower has forced KPIX 5, KRON 4, and KTVU 2 to switch to their auxiliary antennae located toward the bottom of the 977-foot mast that overlooks San Francisco, according to the Sutro Tower website. The problem hasn’t spilled over to the eight other TV stations using the tower or the four FM stations transmitting there.