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tektronix 420a

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nicotronics
Posts: 2
Joined: December 1st, 2018, 3:23 am
Country: Norway

tektronix 420a

Post by nicotronics » December 3rd, 2018, 1:33 pm

Hi,
I been reparing my old tektronix 420a with sucsess after the varistor blew and the Mosfet,
I did a mistake when i was removing the npn transistor q1 which is connected to transformer T2.
There where 2 diodes in series connected from the base to the emitter,
i accidentaly dropped them out, put them back the wrong way i guess,,, they got blown... and now i dont have them installed,
but still with some power from my variac i get voltage now on the output.
but does anyone know the direction and which diodes siting there between the transistors b/e. ?
it series with plastic wrap around.
best regards
NIklas T.
Electronic educated hobbyist.

nicotronics
Posts: 2
Joined: December 1st, 2018, 3:23 am
Country: Norway

Re: tektronix 420a

Post by nicotronics » December 4th, 2018, 1:45 am

anyway, after long search all night actually,
i found out that in my board, there is no r19 or c12.
it has 2 1n4148 diodes in serie with base and emitter in q1,
so i will now be able to fix this tomorrow i think.

:)
best regards NIklas.

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