Re: 2465B DC Balance/Parametric measurement problem


Bob Koller <testtech@...>
 

Well, you may not need to change the caps. How many hours on the scope? I know it can be changed, but if they are low-ish, I would just use it.


From: jmacwilliams
To: TekScopes@...
Sent: Monday, June 4, 2012 10:55 AM
Subject: [TekScopes] Re: 2465B DC Balance/Parametric measurement problem

 
I take back what I said about the suspect U500 (red-in-the-face). I now think it's bad. With the known good U500 installed in the bad scope, I ran the DC balance procedure. It worked and the scope's reference line remains put through all the Volt/Div scales for both channels, parametric measurements now works, and the Trigger voltage reads correctly. Works like a charm. I'm sure it could use a complete cal, but it looks good as is. I'm going to order a U500 and install it in the bad scope. I'll return the good U500 to the good scope.

Thanks for all the help. It certainly helps to have a good second scope to raid parts from, but you guys led me in the right direction.

I guess while I'm at it, I should replace the caps on all the boards that give the most trouble. Is there a list somewhere?

Jim

--- In TekScopes@..., Bob Koller wrote:
>
> Ah, OK, the U500 sounds like it is good then. You really need a calibration generator to run the cal's. It needs to be a 1Khz square wave of the correct voltage. Most function generators can't do it. An HP 3325A might, it has an accurate output attenuator, if it is working right. What do you have?
>
>
>
> ________________________________
> From: jmacwilliams
> To: TekScopes@...
> Sent: Monday, June 4, 2012 9:35 AM
> Subject: [TekScopes] Re: 2465B DC Balance/Parametric measurement problem
>
>
>  
> Good point. Unfortunately I don't have the instruments called out for the CAL procedures, but I might be able to gin something up. BTW, I did install the suspect U500 in the known good scope and it worked fine. Could this just be a bad cal problem?
>
> Serial numbers are B077963 (bad scope), B077964 (good scope).
>
> Jim
>
> --- In TekScopes@..., Bob Koller wrote:
> >
> > Jim,
> >
> > You need to run CAL 2 and 3 first. The different Trig hybrid will need different cal constants, plus the bad one probably caused some too-far-afield constants to be generated. If the CAL's don't pass or correct the problem, then, maybe the Control board has a problem. Is the serial number of your instrument above B05xxx?
> >
> >
> >
> > ________________________________
> > From: jmacwilliams
> > To: TekScopes@...
> > Sent: Monday, June 4, 2012 8:46 AM
> > Subject: [TekScopes] Re: 2465B DC Balance/Parametric measurement problem
> >
> >
> >  
> > With nothing connected to Ch1, Volts/Div at 5V, and input set to GND (it actually makes no difference what it's set to), I can set the reference line to 1 division from the top using the Position pot. Assume the bottom line is numbered 0, then there are 9 horizontal lines, numbered 0 to 8, 8 being the top line. Reference line is on line 7. Here's how it changes as I rotate Volts/Div thru its settings:
> >
> > 5v -- line 7
> > 2v -- line 5.5
> > 1v -- line 3.4
> > 500mv -- line 7
> > 200mv -- line 5.5
> > 100mv -- line 3.4
> > 50mv -- line 7
> > 20mv -- line 5.5
> > 10mv -- line 3.4
> > 5mv -- just below the bottom of the display (line minus something)
> >
> > So there is a pattern: 5v = 500mv = 50mv and so on. This repetition repeats for ch2 when the same deltas.
> >
> > Hope that makes sense. I'm about to try changing the A5 board with a known good one.
> >
> > Jim
> >
> > --- In TekScopes@..., "Patrick Wong" <patwong3@> wrote:
> > >
> > > Hi Jim,
> > >
> > > Back to your OP, how much does the trace move vertically, in major divisions?
> > >
> > > Patrick Wong AK6C
> > >
> > > --- In TekScopes@..., "jmacwilliams" wrote:
> > > >
> > > > Power on self test works with no problems reported. Switching Volts/Div for both Chn 1 and 2 causes the signal to move vertically on the display. I tried running the DC balance procedure and the scope executes the procedure, but the problem doesn't change.
> > > >
> > > > Parametric measurements do not work either. The scope tries to make a measurement, but ends up not finding the signal, and the Volts/Div ends up on the highest scale.
> > > >
> > > > The Trigger voltage reading is also incorrect. Connecting Chn 1 to the Cal signal, the scope will trigger on the signal when the Trigger voltage reading is somewhere -0.5 to -0.1 volts. The Cal signal is truly between 0.0 and 0.4 volts.
> > > >
> > > > I suspect all of these problems have a common cause. I've checked all the test voltages on J119 and all read correctly.
> > > >
> > > > Anyone have any ideas?
> > > >
> > >
> >
>



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