Another CyberMax FM broadcast transmitter came in recently, with a report of no output. After inspection of the PA stage, there was no output from the final stage BLF188xr LDMOS on the pallet amplifier. The whole board looked as if it had been working hard and hot for some time. Rather than risk just changing the LDMOS, a replacement pallet was ordered from PCS, the manufacturer.
This arrived and fitted. sin embargo, after a few minutes of testing on the bench into a dummy load, we noticed that the output had dropped to a few Watts, with a disproportionate amount of current being drawn from the 48V supply. Plenty of exciter drive was present from the previous stage. DC measurements taken around the LDMOS device indicated that we may have had an early failure.
A call into PCS and as usual, great service from Marko. I agreed to take the pallet back and check it. The LDMOS transistor was replaced free of charge. Estos dispositivos no son baratos. With the pallet returned and installed, the equipment was checked, double checked. No shorts or open circuits through the output filter board which is a separate module. No bad solder connection. Asi que, with zero exciter input, the transmitter was powered up. Slowly increasing the exciter power gave us a good output. Temperature probes were left connected to the pallet heatsink for monitoring. All appeared to be stable and was left on soak test for several hours before returning it to the client.
These transmitters are good to work on and modular. Various sections can be broken down and tested, isolated as required. Como se mencionó, backup and service from PCS is very good and we have Marko to that for that.
Oh, the second smaller signal on the spectrum analyser is another transmitter on test, not a harmonic!
Looking at the new BE, black edition range of equipment. Be good to see what these are like.
