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MrBungle · 8th Nov 2018, 11:51 pm

Got a weird one on my hands. Have a 475A here which only sweeps intermittently. When cold it'll quite happily sweep constantly but after it has warmed up it'll sit there for 20-30 seconds and then suddenly sweep 2-3 times and then go back to sleep for 20-30 seconds.

I've checked power supply out. All ok. Have checked every rail voltage on sweep circuit and trigger generator. Works entirely fine in X-Y mode. For lack of a better option I pulled the trigger tunnel diodes out and stuffed them in a working 465 and that triggers fine so TD's are ok. All waveforms are about right when it's working. I've checked both ends of pot travel. I've checked all reference voltages and they're spot on. I've wiggled every transistor and reseated every IC in the signal chain. It just won't keep triggering.

Anyone got any ideas?

If not I'm going to see if I can inject a signal into the loop and follow it round that way. Not ideal though!

8th Nov 2018, 11:51 pm	#1
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Tektronix 475A intermittent sweep Got a weird one on my hands. Have a 475A here which only sweeps intermittently. When cold it'll quite happily sweep constantly but after it has warmed up it'll sit there for 20-30 seconds and then suddenly sweep 2-3 times and then go back to sleep for 20-30 seconds. I've checked power supply out. All ok. Have checked every rail voltage on sweep circuit and trigger generator. Works entirely fine in X-Y mode. For lack of a better option I pulled the trigger tunnel diodes out and stuffed them in a working 465 and that triggers fine so TD's are ok. All waveforms are about right when it's working. I've checked both ends of pot travel. I've checked all reference voltages and they're spot on. I've wiggled every transistor and reseated every IC in the signal chain. It just won't keep triggering. Anyone got any ideas? If not I'm going to see if I can inject a signal into the loop and follow it round that way. Not ideal though!