Topics

Readout pulsing at timebase rate

John Parkins G8KVP
 

Hi All.

Turns out my ghosting of the readout onto the trace is more involved
than I thought.

My 200Mhz 2445B (serial B062351) has a problem with the readout
display. It is pulsing at the same rate as the timebase sweep. At high
frequencies of course this isn't a problem but at lower speeds it gets
a bit annoying. I have the service manual and I have some idea where
to start looking but just wondered if anyone had seen this before and
could help out.

The only error I get is TEST 02 FAIL 53 not at startup but if I go
into the diagnostics. As far as I can see though this tells me I have
a stuck Delta t button, but that doesn't seem to be the case. I have
checked all the voltages and they are all spot on.

Thanks.




--
Best regards,
John mailto:john@...

 

Hi John

I have the same behavior in my 7704A scope. Because I choose to have it this way.

In the Output Signals board, the scope has a switch for an option of readout "free running" or "gated".
If in gated, the readout is displayed at the end of the time base sweep.
I placed it in this mode because I am having some interference with the trace that I thought could be the free-running readout.
It turns out that it is not, it is a modulation by the HV chopper frequency.

So, look in the manual, you may have a similar option.
I like the "gated" mode, since I never use very slow speeds except when I'm playing with the scope.

Ernesto

John Parkins G8KVP
 

Hello Ernesto,

Thanks for the reply. Not an option I can find in the Service Manual
or the Operators Manual. I haven't changed anything either so somehow
this has started by itself. Likewise don't often use the scope with a
slow timebase so it might have been like it for a while, just not
noticed.

I have found a couple of caps which need replacing, so I'll do that
and see if it's still happening.

Tuesday, May 19, 2020, 3:24:26 PM, you wrote:

E> Hi John

E> I have the same behavior in my 7704A scope. Because I choose to have it this way.

E> In the Output Signals board, the scope has a switch for an option
E> of readout "free running" or "gated".
E> If in gated, the readout is displayed at the end of the time base sweep.
E> I placed it in this mode because I am having some interference
E> with the trace that I thought could be the free-running readout.
E> It turns out that it is not, it is a modulation by the HV chopper frequency.

E> So, look in the manual, you may have a similar option.
E> I like the "gated" mode, since I never use very slow speeds
E> except when I'm playing with the scope.

E> Ernesto

E>




--
Best regards,
John mailto:john@...

Albert Otten
 

John,

It's a pity that we only have your description of ghosting here and in your previous messages (because attachments are not allowed). I think you will receive more responses if you make the picture available, for instance by placing it in the Photos section. "Interferes" with the trace is rather vague. Is there a ghost image at the trace and going up/down together with the trace position?
Pulsing at the same rate as the sweep is not the same as showing ghost images. Thinking of Ernestos response, does pulsing mean that the trace and the readout(s) are displayed alternating?
[BTW I'm not really familiar with this "modern" type of readout, so I probably can't help you.]

Albert

On Tue, May 19, 2020 at 07:55 AM, John Parkins G8KVP wrote:


Hi All.

Turns out my ghosting of the readout onto the trace is more involved
than I thought.

My 200Mhz 2445B (serial B062351) has a problem with the readout
display. It is pulsing at the same rate as the timebase sweep. At high
frequencies of course this isn't a problem but at lower speeds it gets
a bit annoying. I have the service manual and I have some idea where
to start looking but just wondered if anyone had seen this before and
could help out.

The only error I get is TEST 02 FAIL 53 not at startup but if I go
into the diagnostics. As far as I can see though this tells me I have
a stuck Delta t button, but that doesn't seem to be the case. I have
checked all the voltages and they are all spot on.

Albert Otten
 

John, at page 2-10 if the Operators manual 070-6860-00 there is a remark/hint about interference between readout and trace. Related to your problem? Albert.

John Parkins G8KVP
 

Hello Albert,

Firstly I'm now thinking the 'ghosting' was a product of other
problems that I've now found along, maybe, with the pulsing readout.

As for the readout, yes if you had set a 1 sec timebase what happened
on the screen was that the readout would flash and the trace would
start across the screen as so on. With a fast timebase the flash
wasn't noticed.

Although I checked the voltages, which were all fine, the ripple
wasn't. I also found the standard leaking caps on the A5 board. So at
the moment the scope is in pieces having those looked at as well as
the Dallas chip. 1991 is the date on that so I thought while I was
inside the thing I'd get that sorted as well.

Once I have that done I'll see if the original problem is still there.

Thanks for the reply

Yes attachments would be useful, if you don't want them, turn them
off.

Tuesday, May 19, 2020, 8:15:08 PM, you wrote:

AO> John,

AO> It's a pity that we only have your description of ghosting here
AO> and in your previous messages (because attachments are not
AO> allowed). I think you will receive more responses if you make the
AO> picture available, for instance by placing it in the Photos
AO> section. "Interferes" with the trace is rather vague. Is there a
AO> ghost image at the trace and going up/down together with the trace position?
AO> Pulsing at the same rate as the sweep is not the same as showing
AO> ghost images. Thinking of Ernestos response, does pulsing mean
AO> that the trace and the readout(s) are displayed alternating?
AO> [BTW I'm not really familiar with this "modern" type of readout, so I probably can't help you.]

AO> Albert

AO> On Tue, May 19, 2020 at 07:55 AM, John Parkins G8KVP wrote:


Hi All.

Turns out my ghosting of the readout onto the trace is more involved
than I thought.

My 200Mhz 2445B (serial B062351) has a problem with the readout
display. It is pulsing at the same rate as the timebase sweep. At high
frequencies of course this isn't a problem but at lower speeds it gets
a bit annoying. I have the service manual and I have some idea where
to start looking but just wondered if anyone had seen this before and
could help out.

The only error I get is TEST 02 FAIL 53 not at startup but if I go
into the diagnostics. As far as I can see though this tells me I have
a stuck Delta t button, but that doesn't seem to be the case. I have
checked all the voltages and they are all spot on.
AO>




--
Best regards,
John mailto:john@...