The Capacitor Plague Hits a Baby Monitor
Good baby monitors are hard to come by. Many tend to be oversensitive, others switch from squelch mode to transmission with a loud hiss that is more irritating than a baby's cry. We were very satisfied with a Tomy Walkabout Digital 1998 baby monitor, until the day it started emitting a squeaking sound.
Changing channels didn't help, but putting the transmitter on battery power temporarily fixed the problem. However, as the battery voltage decreased the power took over and the squeak started again. I thus reasoned that this was a power supply issue; probably insufficient stabilization. Changing a 100μF 16V capacitor that was near the battery terminals (see picture on the left) with a new one fixed the problem for good.
Six months later the problem reappeared. I thought that it was unlikely that the capacitor I replaced had failed again. Also, this time to stop the squeak we had to put the receiver on battery power. I therefore reasoned that this was a faulty capacitor in the receiver module. Again I changed the 100μF 16V capacitor near the receiver's battery terminals (see picture on the right) with a new one, and the problem got away. I had read about the capacitor plague affecting computer motherboards, but it seems that baby monitors are not immune.