KT,
I money is on U506 has a bad input at pin 15. Lots of current's flowing into it, but it shouldn't be. Probably got zapped with a big dose of static electricity at the ring.
Jimmy
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--- In TekScopes@..., "lldskjfoi" <k.templin@...> wrote:
I have 2.5 at both ends of R106.
1.9 and 1 at R105.
--- In TekScopes@..., "Tom Jobe" <tomjobe@> wrote:
What is the voltages on either side of R105 and R106?
It seems like C111 and U506 are the only possibilities if the voltage leaving R105 more or less agrees with what you see arriving at U506 pin 15.
tom jobe...
----- Original Message -----
From: lldskjfoi
To: TekScopes@...
Sent: Thursday, September 20, 2012 6:04 PM
Subject: [TekScopes] Re: 2247A Channel 1 issue
10k and 10k. What do you thin? the only thing left are the caps or the U506 itself.
KT
--- In TekScopes@..., "Tom Jobe" <tomjobe@> wrote:
>
> What are the resistance readings across R105 and R106?
> That might help narrow the search down.
> tom jobe...
>
>
>
> ----- Original Message -----
> From: lldskjfoi
> To: TekScopes@...
> Sent: Thursday, September 20, 2012 5:19 PM
> Subject: [TekScopes] Re: 2247A Channel 1 issue
>
>
>
>
> I get 8.2 and 8.2 as well.
>
> KT
> --- In TekScopes@..., "Tom Jobe" <tomjobe@> 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" <tomjobe@> 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" <tomjobe@> 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" <k.templin@> 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
> > > > >
> > > >
> > >
> >
>
