[raymo]

Thanks for the replies.
My LG DVD player is RCA only, so I bought an RCA to HDMI converter and
a digital to analogue converter for the phones, on ebay. The DVD works fine.
When the headphones didn't work, I tried the D to A converter on my other TV [TCL] and it worked o.k. which makes me think the problem is within the TV; either there is something somewhere that I need to select or activate,
or the TV just is not sending audio signal to the converter for some weird reason. In Settings- Sound- the headphones selection is greyed out saying
"this service is unavailable". The TV is a Hisense 65U7KAU Oh, and the
Sennheiser headphones connection is RCA only. The Chinese converters have no company name on them. I do get static through the phones which changes as you rotate the tuning wheel on the phones, just no trace of audio signal, could it be that wavelengths covered are not compatible with this particular brand of TV, although that seems bizarre. The converter is USB powered, and the power light illuminates when the TV is turned on.
raymo