Troubleshooting Ronja Tetrapolis

We suppose you are having an installed link where something went wrong. You want to fix the link.

Go to the roof and check by eye if the other side is shining.
Look into local TX and check if it's shining and if it's not covered by water droplets from inside.
Move around the roof and check if the maximum is aligned with local receiver. If not, realign the distant transmitter.
Connect a voltmeter to local RX's RSSI and check if there is signal
Play a bit with the RX alignment nuts and make sure the RX is aligned in the optimum direction.
Perform bit error rate measurement of the link. If you cannot, do packetloss measurement of the link.
Perform bit error rate measurement for Twister2 on each side. If you cannot, perform packetloss measurement for Twister2 instead.
If you haven't find the fault now, it must be in the receiver or the transmitter.
Take out receiver and transmitter on one side and perform Noise Equivalent Distance measurement.
Repeat the last step for the other side of the link

Causes of dead receiver

Lightning strike - replace Q101 transistor
Water in the electronics for some time - throw away and make another receiver (this one will never be reliable again)
Cold joint started to manifest itself - remelt all joints with a bit of rosin flux

Water in the electronics for some time - throw away and make another transmitter (this one will never be reliable again)
Cold joint started to manifest itself - remelt all joints with a bit of rosin flux