Re: Puzzle of the day: 465b will not trigger on channel 2 SUCCESS!


 

I looked the transistors up earlier. Q1746 and Q1954 have an Ft of
900 MHz, Ccb of 3 pf, and are similar to a 2N4258 or PN4258.

Any PNP RF transistor like an MPSH81 should work but you can use
2N3906 transistors temporarily. Matching is not needed because
adjusting R1835 will trim out any offset.

On Sat, 18 May 2013 03:34:55 -0000, "jeffbathwater1"
<jeffbathwater@gmail.com> wrote:


I checked those transistors as you requested... here is a link to the
schematic with my voltages:
465 schematic 2 <http://www.horusdevelopment.com/tmp/465bSchematic2.jpg>

Q1845 is showing +15.02 at the base not +9.5. I tried swapping Q1845
with Q1045 from CH1 but still no trigger on CH2!

Hold on!
I was just about to post this when I thought I would try swapping Q1746
with Q1150 from CH1... and yes I get a steady trace on CH2!! You were
spot on!
The transistor is a SPS246. Do you think it will be part of a matched
pair or can I just use any equivalent device?

I appreciate all the time and effort you and Tom put into help me solve
this. I have learnt a lot and it has fueled me to go and read up more to
understand more about the scope. Do you know of any good books that
would help?

I'm sure you need a rest from all my questions.. thank you again David.

Dave

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