ifi Retro Stereo 50 Service Manual page 7

Then you will see this:
- Remove the 4 x 2.0mm screws and take out the DAC PCB
- At this point you can remove the tubes whilst the main PCB is still secured.
- Place the tubes in a protected area so they don't get damaged.
- Remove the ribbon cables attached to the main PCB.
- Unscrew the main PCB and remove.
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Service Manual