Revox B226s CD Player display backlight

[robin0577]

Background for anyone not familiar with the beast... It has a liquid crystal display, backlit with a green EL strip driven from a small inverter.

I have this CD player and the matching cassette deck. Both arrived with dead backlights. I have replaced the EL strips on both with brand new ones from Nagravox. The cassette deck lit up brightly first time and has stayed lit.

The CD player didn't light up. So I started looking at the inverter, and it soon became clear that the op-amp had burned out, and discolouration of the PCB suggests it had been running hot for some time. Now the display lights up briefly but the op-amp quickly gets hot and shuts down, even with a small heatsink attached and the brightness turned down low. It still runs hot with the EL strip disconnected. Clearly there is too much current being drawn.

So the question is, where do I go from here? Transformer short possibly? The transformer is based on an RM series core and bobbin, looks about RM12 size to me. I'm aware that it can be tested for shorted turns using a scope, but I'd need a bit of guidance for how to do that...

Or is the op-amp not up to the job?

The schematic specifies an L272, which I think is rated for 700mA (in it's 8 pin DIP format), and that's what I have fitted. However the burned out part fitted in the machine previously was a TCA0372-DP1, rated for 1A. Did the manufacturer make this change on later models, or has someone upgraded later do you think?

Edit to add... On the machine I have, there is a 2k2 trimmer in place of the final stage feedback resistor for brightness control. This is a legit manufacturer PCB redesign, not a bodge.

Schematic attached...