Sony Receiver Stereo Lamp Problem

[markallen]

Everything works on this clean STR-6046A but for one problem: The FM Stereo lamp was not illuminating.

Assumed it was a burned out bulb. It wasn't labeled, so to establish what lamp I'd need, I used my DMM, which read 6.9 volts DC - but I quickly found that wasn't only on an FM stereo signal: that voltage remained constant ALL the time, across the FM dial, both for stereo and on the (rare) mono station.

Adding to the mystery, this voltage remains steady for EVERY OTHER FUNCTION as well! Phono, Aux, AM, mic, nothing changes, nor does using the stereo/mono switch.

One more thing: I sometimes use resistor-equipped LEDs to replace these lamps. Here, the LED stays on as described, but standard incandescent grain-of-wheat style bulbs won't light up at all, even those rated at 6 volts.

Why would this voltage originating from the tuner board remain constant for all functions? Not sure where to go from here to trouble-shoot this problem. Also, HiFi Engine has a schematic for the 6046, but not the 6046A.

Any assistance appreciated.

 

[TPettenati]

Sounds like you are measuring from chassis to the bulb. That won't work. Need to measure across the bulb. The way that indicator works (I think) is one side is always tied to voltage, and the other side is pulled down to (near) ground on the tuner board, to turn the lamp on. Best to pull the lamp and check continuity.

 

[markallen]

Sounds like you are measuring from chassis to the bulb. That won't work. Need to measure across the bulb. The way that indicator works (I think) is one side is always tied to voltage, and the other side is pulled down to (near) ground on the tuner board, to turn the lamp on. Best to pull the lamp and check continuity.

Thanks for the response. Actually, I'd cut off the bulb assuming it was bad, so I was in fact measuring the voltage from the bulb's wires. No chassis connections on this project!