This scope has been up and running for a few days now and all other functions are working.
Horizontal gain is off slightly (from my time mark generator).
Before I do a calibration I want to go ahead and recap and diode the power supply.
I have read about the faulty diodes.
Has anyone had experiance / knowledge on which caps to repalce?
I have read that the tall metal cans and the high voltage ones do not need to be replaced. Their are not too many left after that.
Anything else that should be replaced?
Voltages at the test points are within spec.
Thanks
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--- In TekScopes@..., "Tom Jobe" <tomjobe@...> wrote:
Your 2247A success made me think about what could we learn from your adventures.
If you simplify the problem, you have a 2.5 volt supply going through three things in series, R101, R105 and whatever leak(s) you had.
We know the value of the two resistors and about how much voltage they dropped together, so a little calculation tells us that the current is on the order of .09 milliamps through this circuit.
The voltage remaining after R105 and this .09 mA current tell us the leak(s) amount to something like 10,000 Ohms.
That is not much of a leak, so I guess it could have been caused by many things beyond bad components.
I don't have enough experience or knowledge in electronics to know how much of a leak could be caused by dirt, moisture, flux residue, etc, etc.
So those are some more things I need to learn more about.
tom jobe...
----- Original Message -----
From: lldskjfoi
To: TekScopes@...
Sent: Friday, September 21, 2012 10:34 PM
Subject: [TekScopes] Re: 2247A Channel 1 issue
The culprit was C111. Sniped one end and bingo.
Amazing what a 10 cent part can do.
Thanks Tom I really appreciate your help. You start overthinking the problem and going off in a wrong direction.
It's nice to have those "outside eyes" helping.
Snipping the cap was a great idea.
KT
--- In TekScopes@..., "Tom Jobe" <tomjobe@> wrote:
>
> Well, unless I missed something you are down to C111 or U506 as being the culprit.
> I would carefully lift one leg of C111.
> It is near U506 pin 14, slightly further from the front of the scope.
> It might also be orange in color.
> tom jobe...
>
> ----- Original Message -----
> From: lldskjfoi
> To: TekScopes@...
> Sent: Thursday, September 20, 2012 6:27 PM
> Subject: [TekScopes] Re: 2247A Channel 1 issue
>
>
>
>
> 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
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
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