I get 8.2 and 8.2 as well.
KT
--- In TekScopes@..., "Tom
Jobe" wrote:
>
> I just checked R101 and R102
on a bare 2246 mainboard and they both measured 8.2k ohms in circuit.
>
If the resistance is correct on your scope, then something is drawing enough
current to drop 0.7 volts across R101.
> Nothing in that simple circuit
looks like a suspect to me, no nasty 10uF to 47uF tantalums, etc.
> tom
jobe...
>
>
>
> ----- Original Message -----
> From: lldskjfoi
> To: TekScopes@...
> Sent: Thursday, September 20, 2012 1:20 PM
> Subject:
[TekScopes] Re: 2247A Channel 1 issue
>
>
>
>
> Thanks again for the responce. I think we are getting there.
>
> Using cahannel 2 as the "working reference"
>
> pin 12
(channel 2) on u506 goes from the +2.5 to +1.4 when a 10x probe is
connected.
>
> pin (15 channel 1) on U506 goes from +.9 to +.6
with the probe connected.
>
> Checking R102 for channel 2 it has
+2.5
>
> R101, (channel 1), shows +2.5 in but only +1.8
out.
>
> What are your thoughts? Is it simply a bad resistor or
would one of the cap, C111 cause the voltage drop?
>
> Thanks
again, KT
> --- In TekScopes@..., "Tom
Jobe" wrote:
> >
> > For the record, I slid
the cover back on a very dead 2246 and checked pin 12 and pin 15 of U506, they
both had +2.49 volts with no probes attached.
> > This scope does not
have any lights on the front, and none of the buttons work, so I could not see
the reading I would get at ground, or with a 1X or a 10X probe.
> >
tom jobe...
> >
> >
> >
> >
>
>
> > ----- Original Message -----
> > From: lldskjfoi
> > To: TekScopes@...
> > Sent: Thursday, September 20, 2012 8:28 AM
> > Subject:
[TekScopes] Re: 2247A Channel 1 issue
> >
> >
> >
> > Thanks, thanks the info I was looking for. I started getting
into the schematic last night I saw the path to U506. Will start checking it
out.
> >
> > Also notice just letting the scope run with
the probe attached the attenuation factor jumps back and forth- correct /
incorrect. Does not change with no probe attached so it is getting an
intermitant signal.
> >
> > KT
> >
> >
--- In TekScopes@..., "Tom
Jobe" wrote:
> > >
> > > Maybe start
by looking at the #1 "Vertical Inputs" schematic to see the simple circuit
which starts at the junction of R101, C101 and R105 for channel 1.
>
> > That junction point is connected to the readout ring behind the BNC
connector, so you could test for continuity and shorting to ground,
etc.
> > > If you compared both ends of R101 and R105 (Chan 1)
with those of R102 and R106 (Chan 2) you might see if the readout voltage is
getting that far.
> > > If that looked okay, you could go to U506
and see if it arrives at pins 12 and 15 as you would expect.
> > >
With the scope on its back, you have excellent access to all of these
resistors and U506 (16 pin DIP), with the blue outer cover slid back the width
of your hand.
> > > From reading the service manual, it appears
that the readout signal gets changed to a digital signal at U506, but is a
simple voltage up to U506.
> > > tom jobe...
> > >
> > >
> > >
> > >
> > >
----- Original Message -----
> > > From: lldskjfoi
> >
> To: TekScopes@...
> > > Sent: Wednesday, September 19, 2012 9:08 PM
> >
> Subject: [TekScopes] Re: 2247A Channel 1 issue
> > >
>
> >
> > >
> > > Some more checking shows
channel 1 is not getting the code signal from the probe. Any idea on this
circuit?
> > >
> > > KT
> > >
>
> > --- In TekScopes@...,
"lldskjfoi" wrote:
> > > >
> > >
> Hello everyone.
> > > >
> > > > Initial
test show an issue with channel 1.
> > > >
> > >
> Any direction on where to start?
> > > >
> >
> > Channel 2 displays inputs correctly from the FG.
> > >
>
> > > > Channel 1 displays 10 times the amplitude for the
same signal.
> > > >
> > > > Example a 1 volt
sine wave on channel 2 displays on the voltmeter function correctly at ~1v and
2 divisions at .5v / div.
> > > >
> > > > The
same signal on channel one reads as ~10v. When set to 5v / div it fills two
div.
> > > >
> > > > Thanks, KT
> >
> >
> > >
> >
>
