Author Topic: Tektronix 2465 power supply  (Read 1509 times)

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Offline dan3460Topic starter

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Tektronix 2465 power supply
« on: September 11, 2016, 03:25:26 pm »
I have been fixing scopes for a while, normally is the power supply. I have been successful until now.
After plugging the scope for the first time you get a flash of green but then nothing, no lights on the front, the fan is running.
I opened the scope (this is my 4th 2465) and looked at the 2 0.068uf safety caps, both where cracked. As I needed to take the boards out to replace them I replaced all the electrolytic including the 2 big 290uf beside the fan motor.
I installed the boards back and still getting the same result. Just a flash of green on the screen and nothing. I don't hear the clicking of the inverter trying to start, but what throws me off is that all voltages on test plug on the main board are ok (there are 9 different voltages there all ok).
I scoped the 3 teeth comb that gives power to the inverter board, I was expecting to see a steady voltage but I get the same 60hz +/- 60V on each teeth. So I'm lost as to what to look for.
Also there is a voltage reference between pin 4 of T1020 and pin 1 of T1050 that should be 264V over the Reference line. I only get around 140V, also the 12.6V at the collector of Q1062 is around 7V. So thinking that maybe the line voltage selector was bad (as open is the setting for 240V mains) I poke around and I tested the voltage at P204 and P205 I only get 90V. Don't know if that is normal, it seems that the EMI filter is eating 30V.
 


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