I just bought a ToteVision HY-5500 portable television from a thrift shop, and it's not working. When connected to the required 12V, from an adjustable power supply, it initially draws about 70mA, then drops to about 50mA over the course of a few seconds. The tube is in good cosmetic condition, the filament lights, but no picture shows. I can't hear the characteristic flyback whine. I assume the step-up circuitry is to blame, but I don't know how to fix it. Can anyone help troubleshoot this problem?