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Old 25th Jul 2020, 8:57 pm   #6
Join Date: Mar 2015
Location: Milton Keynes, Buckinghamshire, UK.
Posts: 69
Default Re: Marconi TF2431 Counter Service Manual / Schematic

Well the ferrite bead on Tr7 base didn't work.

I tried smaller values of peaking capacitor but TR7 still oscillates even with values as low as 4.7pF.

It makes me think there must be something else going on.
The copper ground area around TR7 is wide and looks like it's low immpedance.
The 5v rail decoupling looks ok.
The PCB tracks around the transistor are short.
The metal transistor can is grounded as it should be.
I'm baffled.
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