On 25 Sep 2012 at 0:52, TekScopes@... wrote:
Posted by: "pdxareaid"
Date: Mon Sep 24, 2012 5:48 pm ((PDT))
i'm not sure of the best way to post this followup for all previous
responders see. so, i'm replying to my original post...
i spent some quality time with the new toy today. i guess it just
needed some attention...
i turned it on and found i was getting one spot on the screen rather
than a massive glow (i kept it de-focused as it was full intensity.) i
looked around at the tantalums that had one smoking yesterday and
noticed a solder bead on one of the three. i poked it and it fell
off...and a trace slowly snapped back. some adjustments and things
were sweeping! how the heck does a solder bead on the outside of a
tantalum cause this? was there a cold solder i tweaked at the same
time?
so since it appeared it was not going to catch fire this time, i let
it run and things stayed nice and stable. i turned it off and tested
all of the transistors in the area of the smoking tantalum (this is at
rear of sweep logic board btw). they all appear ok.
man, you people with socketed transistors have it easy. try testing a
transistor on a 465M. you have to desolder it...no sockets! (except
about four i found that probably should not have been there lol) no
sockets is part of the "ruggedized for the military" modification.
so, things are working fine with a few mechanical probs. i found a
loose transistor preventing the x1 light on chnl 1, stuck it back in
and that prob is fixed.
the horizontal position pot is wonky. lots of play. i've seen this
before on the 465M. i guess 35yrs of use takes it's toll.
the main intensity pot is dirty or toast. i will probably attack it
soon.
but careful fiddling and it gets you where you want to be.
the B delay pot knob is offset to 0.2 when bottomed out. and it shows
on the trace. i think this was previous owners way of correcting for
improper registration on the trace. likely a simple calibration tweak
will fix it and i'll rezero that pot knob.
this is a significant one:
the A trig view only shows a flat line but everything is triggering
properly (including B sweep stuff). possibly a loose jumper wire etc.
i'll chase it soon.
since it was staying up (for 2 hours now) i took PS readings at test
points.
voltage VDC, ripple mV p-p
supply voltage spec ripple spec
+110 108.2 106.7 to 113.3 16 20
+55 54.9 54.62 to 55.39 3 4
+15 15.00 14.75 to 15.26 1 2
+5 5.01 4.92 to 5.09 1 2
-8 -8.01 -7.86 to -8.14 1 2
not too shabby. i may take a look at getting +110 closer to 110. i
am still nervous about ps filter caps because my 465M worked for a few
hours then tore itself apart with failed caps and exploding
transistors. i'll keep an eye on it for a while. it would be nice
not to have to recap this thing. (i know about reforming but i'd
rather recap and be sure)
all the other bells and whistles seem to be working x10-mag etc. and
timing and vertical deflection look right on.
So, not a very exciting fix but so far i have a nice working 465B but
i'm quite sure why :-o phil
Well done!
The Tant's with what looked like a blob of solder, are failed parts.
That blob, was molten Tantalum Metal ejected from the part when it
failed. You got lucky clearing the short by knocking off that blob.
Best the part be replaced for a long life from now on.
Not sure about the A-Trig View issue. I presume you had a signal for it
to trigger on, and that was selected. But maybe just a dirty siwitch
contact, or something related in the vertical logic. For now, it sounds
like you've a 99% working instrument, and a massive grin no doubt.
Dirty pots, just "Exersize them" back and forth with the power off, and
they will then improve with use. Some can be stripped apart and
cleaned, but very fiddly to do, and needing care not to damage the track
etc, plus finding out what the correct lube to put back in there is, is
not easy. I'm guessing silicone grease, but I don't know for sure.
Best Regards.
Dave B.
