Re: more scope questions
- From: "Stephen Cowell" <scowell@xxxxxxxxxxxxx>
- Date: Sun, 17 May 2009 21:42:42 -0500
"Phil S." <psymonds@xxxxxxxxxxx> wrote in message
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"Stephen Cowell" <scowell@xxxxxxxxxxxxx> wrote in message
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Steve:
I'm looking at a block diagram of an oscilloscope, located
via Google. The CRT diagram has ten connections:
1.) +18KV Anode. Not through the back, through the side, with a rubber
cup.
2.) Horz Amp, 2 connections for horz plates.
3.) Vert Amp, 2 connections for vert plates.
4.) Three screen grids, presumably for isolation, acceleration, etc.
All connected together.
5.) One screen grid, for beam on/off. Used during blanking (retrace).
6.) One cathode, at -1850VDC.
Not shown... heater connections, of which there should be two. Minus one
(anode),
that leaves either eleven (screens separate, a la EL34) or nine (a la
6L6). You have
eleven. Look some more... find the wire from the HV section to the anode
on the side
of the tube. We won't go farther until you've located this and confirmed
it.
__
Steve
.
Look here: http://home.comcast.net/~psymonds/BK1472.htm
for a picture of the tube socket. You will see a black wire soldered to a
metal collar that runs to the PCB. Anode?
Nope... shielding. You'll *never* find 10kV connected to
something as big and uninsulated as that. You're missing
it.. perhaps underneath the side of the tube. Rubber cap
on side of tube. It's there, you'll find it.
Pin numbers and wire references are at the web.
I'm thinking 7 and 8 are a pair and maybe 1 and 3 are a pair or maybe 14
and 1 are a pair. Guessing white on 4 and 6 are filaments?
Indeed, there are 11 pins used! Plus the anode on the metal collar.
What sort of voltage will there be on the Horizontal or Vertical plates?
I realize you don't have specifics. How 'bout bigger than a toaster and
smaller than a fridge?
Probably in the hundreds of volts. Your pictures show other problems,
though... the slanting traces show poor voltage regulation; one of your
pictures shows the trace actually at least one division over on the right
hand side; this means that the connection to the tube is OK, otherwise
it'd stop at the middle dead as a doornail, more like the bottom pic.
Another thing you can see... the cal trace is appearing several times,
with big gaps in it (look at third from bottom); this point to the retrace
and
horz sync not synchronized. Your horz position knob (upper right)
is in the middle... what happens when you turn it to the right?
Every connector in there is a possible candidate... wiggle/grind
them all, gently! The slanting lines point to a cap dislodged...this
thing took a lick, right? Examine all circuit boards for broken
solder and broken traces... particularly near big heavy things like
electrolytics. Most of all... have fun! Remember, you're saving
money, right?
__
Steve
..
.
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