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Electronics => Repair => Topic started by: Zenwizard on March 03, 2019, 10:58:20 pm

Title: Repair of a Tek 284
Post by: Zenwizard on March 03, 2019, 10:58:20 pm

So it seems I have a sick Tek 284. Attached is the scope captures of an odd transistor failure/ possible bias issue. I think. This is a push pull pulse in to the tunnel diode. The scope shot is Q135 and Q 145.
Q135 is the positive drive and is yellow. Q145 is the negative drive and is the pink trace. The fist picture is the base drive signal the second picture is the output of the same transistors at the collector. Then questions now is do I have a partially shorted q135 or is it a biasing issue. The drive signal is slightly high on the base with a little dc. I am just not sure if that will cause this much weirdness?
Thanks for the help with a weird one.

Title: Re: Repair of a Tek 284
Post by: Zenwizard on March 09, 2019, 12:42:44 am

It might be a possible bias issue with the driver transistors some where. The base on the positive rail is reading a little high about 0.6V This might not be allowing the positive side to turn off fully.