IR-Blaster SB3's not responding

I am endeavouring to set up IR-Blaster on any of my four SB3's. As a first test I checked that the headphone output worked and found that three of the SB3's have no output from the headphone socket - doubtless due to the 10mF capacitors having failed (as reported elsewhere in the forum). This leaves me with one good SB3. I have verified from the debug log that the test commands provided on the IR-Blaster settings page are being sent by the server to the SB3 but neither of two different IR senders (1 borrowed from a Logitech Harmony & 1 oem) work.
I am running the latest 8.3.0 nightly.
Is anyone still using the plugin successfully and are there any recommended solutions?
As a separate issue, I do intend to replace the capacitors at some stage but the phono and toslink outputs are still working fine.

John C