My RME Babyface Pro FS is a superb sounding audio interface but after six years of use it had started giving me problems. The RH headphone channel was cutting out from time to time and the problem was getting worse. The obvious first thing to check would be the cables to my headphones, and then try the 3.5mm headphone socket but both outputs had the same issue. It sounded to me like a problem with the Digital to Audio Converter (DAC) since I knew both headphone jacks were fed by one output from the DAC according to the diagram in the RME manual. I was quoted a fixed price repair of £240.

After getting it apart and tracing the route from the DAC to the headphone outputs, I realised the headphone amplifiers are simple 8-pin dual op-amp ICs shown below. I was surprised to find the RIGHT channels (for both the ¼" and the 3.5mm jacks) are on one chip and the LEFT channels are on another chip. Maybe it's designed this way to achieve the ultimate channel separation? There are three of these Texas Instruments OPA1688ID dual op-amp chips in the Babyface and the photo below shows their layout.

I guess the middle IC provides the Main Out L+R. The bigger 44-pin chip on the left is the DAC.

Getting the Babyface apart is really simple, the jog wheel can be prised out with a couple of guitar picks and then just four screws on the bottom hold it together. Another couple of screws inside hold the main board to the body. Disconnect the ribbon cable to the top display (by flipping up its locking tab) and you can open it up like a clam. With the display disconnected you can still operate the thing from TotalMixFX.

The fault was getting worse at this point and I realised the headphone jack actually had 4.6V DC on it when it went wrong. I found it would work okay at very low volumes but crap out at any useful level setting - by now I wasn't plugging in expensive headphones but had wired a 1K resistor and LED across the RH channel it would display when the output jumped to DC. With a finger on the Right Channel IC, I was able to be sure that I had isolated the problem—that chip was getting too hot to touch! Cooling it down would let the channel work again for a bit longer but it needed to be replaced. Nothing else on the board was getting hot.

After ordering a replacement from Mouser Electronics (https://mou.sr/41aJwdv) and replacing the chip everything now works perfectly. It's not a difficult soldering job but is a bit fiddly - they are pretty small but surface mounted. Total cost £1.62 plus a rather hefty delivery charge.