Installed No optocoupler according Midi Standard

After my Fatar Studio 900 did not want to work with the adapter, I have found with MIDIOX that the data bytes that have been received by the adapter, were not correct. Apparently contained bytes too many "high bits".
After swapping cables in the Midi-Through a Yamaha expander voted bytes received. Also funzte the adapter to another electric piano.
Further research showed that the Internet is full of users in the audio forums, which have the one or other MIDI device from reputable manufacturers also problems. So seems to be something wrong with the wiring of the adapter. Thereupon I opened him tonight and behold:
The Chinese have saved on the components fitted and no optocoupler and freewheeling diode in the Midi-In. Instead, the output driver must pull down on Pin 5 of the Midi-out on the transmitter the Rx pin on the adapter .mu.C via a 1k to the 5V from the USB plug.
If the level in the device, these 5mA can not drive, so the bits do not agree on the UART-input of the controller.
This circuit does not correspond to the Midi phsical Layer standards.
This provides that the transmitter from the receiver is completely galvanically isolated and drives the photodiode of an optocoupler in the receiver via the MIDI Out jack !!
Now comes the good message:
The pads for optocouplers and diode are available and the optocoupler costs 0.27 to 0.32. So I'm going to convert the adapter times daily.

However, since dealing here with a real violation of the Midi-electrical rules, there is only 1 star.

Update 06.02.2013:
Retrofitting program carried out today:
R11 -> 0 Ohm -> away
R3 -> 1 kOhm -> 680 Ohm
D1 -> BAS21 added
R5 -> 220 Ohm -> added
U1 -> LTV817B -> Add.

Midi-in works with my Fatar at its finest!

However, it remains at the 1 star, because not every musician is in this world also electronics :-)