Hi Gang,
Well, I'm at it again. I have on the bench an SB 520 that had no transmit. The owner said he had high SWR's and it quit. I checked the final with my transistor tester and it was bad so I replaced the driver and final with brand new (not fakes) 2166 driver and 1307 final. I also replaced the tantalum cap (179) with a 25 volt version. It still did not transmit. I had .7vdc on both bases and 9 volts on the collectors. The collectors are supposed to be 4.7vdc based on the schematic so 9 volts was wway too high. I went to set the bias on them and was able to set the driver to 60 ma and when I went to set the final to 50 ma it initially set for a second then drifted to over 400ma and will not come back down. Any thoughts?
Well, I'm at it again. I have on the bench an SB 520 that had no transmit. The owner said he had high SWR's and it quit. I checked the final with my transistor tester and it was bad so I replaced the driver and final with brand new (not fakes) 2166 driver and 1307 final. I also replaced the tantalum cap (179) with a 25 volt version. It still did not transmit. I had .7vdc on both bases and 9 volts on the collectors. The collectors are supposed to be 4.7vdc based on the schematic so 9 volts was wway too high. I went to set the bias on them and was able to set the driver to 60 ma and when I went to set the final to 50 ma it initially set for a second then drifted to over 400ma and will not come back down. Any thoughts?