17-11-2014, 07:11 PM
Well that bout of flu turned out to be two weeks of banging on Death's door asking to be let in followed by another few weeks of endless coughing. Glad to be finally over it and I certainly hope none of you guys are unfortunate enough to catch it. My flu jab was set for 3rd Nov but the real thing caught me first this time.
Anyway, back to the scope. I was pretty sure I'd narrowed it down but having now replaced all the relevant components in that part of the circuit - still no trigger output. I've managed to scan the documentation so I've attached the latest summary - showing the components I've replaced and the static DC voltages at the various nodes in that part of the circuit.
Originally resistors IR240 and IR244 clearly showed signs of overheating so I replaced them with 0.1% tolerance half watt versions. The replacements get hot too and based on the voltage drops I've measured they are sinking more than 500mW so, not good.
I have good signal up to the transistors ITR55 and 56. It then splits off and continues via ITR57 and 58 and from there off to the display - that part is fine. It should also go via ITR59 and 60 to the trigger amp but there is no signal at either emitter.
As I've said before, my knowledge of the world of three legged fuses is somewhat limited so I'm open to all reasonable suggestions as to next steps.
In the attached diagram, all the comps in red have been replaced (plus ITR61). The two resistors shown in pink (241, 218) are in very difficult locations so would require some major dismantling to get at. They measure fine so I've left them in for now.
Cheers, John
Anyway, back to the scope. I was pretty sure I'd narrowed it down but having now replaced all the relevant components in that part of the circuit - still no trigger output. I've managed to scan the documentation so I've attached the latest summary - showing the components I've replaced and the static DC voltages at the various nodes in that part of the circuit.
Originally resistors IR240 and IR244 clearly showed signs of overheating so I replaced them with 0.1% tolerance half watt versions. The replacements get hot too and based on the voltage drops I've measured they are sinking more than 500mW so, not good.
I have good signal up to the transistors ITR55 and 56. It then splits off and continues via ITR57 and 58 and from there off to the display - that part is fine. It should also go via ITR59 and 60 to the trigger amp but there is no signal at either emitter.
As I've said before, my knowledge of the world of three legged fuses is somewhat limited so I'm open to all reasonable suggestions as to next steps.
In the attached diagram, all the comps in red have been replaced (plus ITR61). The two resistors shown in pink (241, 218) are in very difficult locations so would require some major dismantling to get at. They measure fine so I've left them in for now.
Cheers, John
Time flies like an arrow, fruitflies like a banana!
