Yeasu FT-991A – M2TS- Service BV

This Yeasu FT-991A ALL-BAND, MULTI MODE PORTABLE TRANSCEIVER apparently failed after a lightning storm, so investigating the printed circuit boards for flash-overs or burn marks was the first task at hand.
Many hours later no flash-over or burn marks were discovered on any circuit board and after reassembling the device, checking the necessary voltages in the power section and startup circuit were the next step. Although the necessary voltages reached the microprocessor on the front-board and the power signal from the microprocessor was send to the startup relay circuit, the startup relay did not switch, but when we shorted the open relay contacts briefly the device came to life…

**^{Since the smallest SMD components are as big as the dot of a pen, you can image the difficulty of repairing these devices …}**

^{The voltages on the switching transistor for the startup relay did not quit seem right, so removing it and attaching a temporary resistor made the receiver come to life. Now we can test the transceiver thoroughly before ordering any components, as their might be more issues that surface…}

While testing the transceiver in RX an TX mode, the specified power consumption was strictly monitored and always met the specifications according to the service manual. Hooked it up to our communication radio tester, in all bands, no issues whatsoever … So in my opinion the failure of the switching transistor was purely coincidental and not related to the lightning storm at that moment … Nevertheless we also changed the first stage buffering dual pnp/npn pre-biased bipolar transistor as well as the two smoothing capacitors on the right.

^{After installing the new components, cleaning the flux residues and a brief function test, time to reassemble the transceiver, connect the antenna and give it a final test. Unfortunately in this brief video the repeater we are trying to reach is not really in the mood for answering… Anyway, later that evening we can test the transceiver on maximum TX power in an hours long conversation with different Ham radio friends without any issues, and the transceiver is still in use a of today with it’s satisfied owner …}