7704A - Delayed Sweep Intensity Too Bright


n4buq
 

The delayed sweep intensity is way too bright in my 7704A. If I understand it correctly, a time-base sends a signal to the mainframe to indicate the delayed sweep is active and the mainframe knows to make that a higher intensity trace.

Is there a separate adjustment for that intensity? I haven't attempted to set the CRT grid bias and that could be part of the problem but it appears a signal standardizer may be required for that and I don't have one of those and am hoping that I can at least reduce that excessive brightness just a bit without having to get one of those first.

I know this might sound like a "golden screwdriver" sort of thing but if I could just reduce that intensity for now, it would be a big help.

Thanks,
Barry - N4BUQ


Mark Vincent
 

Barry,

It sounds like the time base you are using is the source of the delayed sweep. Some have an intensity control for the delayed sweep. A 7B92A is an example. The 7704A has two main intensity controls, the one at the top and two above the plug-ins. One of the two could be turned up. I have the two about 70% up and adjusted the crt bias so that the main intensity is about at the 11 o'clock position to get a trace visible. Controls in the Z circuit were adjusted. Those will alter intensity and focus.

Mark


n4buq
 

Mark,

Intensity settings for normal traces are about right. The main intensity is somewhere near mid-range and the A/B intensity controls are in the 9:00 to 12:00 range (or less).

I'm using a 7B53A and when I pull the time/division knob to its outward position for a delayed sweep, the delayed trace is very bright. I presume the intensity of the delayed sweep is an independent setting from a normal trace in the main frame but not sure.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, October 21, 2021 9:55:27 AM
Subject: Re: [TekScopes] 7704A - Delayed Sweep Intensity Too Bright
Barry,

It sounds like the time base you are using is the source of the delayed sweep.
Some have an intensity control for the delayed sweep. A 7B92A is an example.
The 7704A has two main intensity controls, the one at the top and two above the
plug-ins. One of the two could be turned up. I have the two about 70% up and
adjusted the crt bias so that the main intensity is about at the 11 o'clock
position to get a trace visible. Controls in the Z circuit were adjusted. Those
will alter intensity and focus.

Mark



Mark Vincent
 

Barry,

See if having the A/B intensity turned up and the crt bias up (more negative at the grid) helps. If your S/N is <210000, check Q320, Q322, Q420 and Q422. These are in the two heatsinks on the right side top. If these are leaky, use KSP10BU. I do not see any internal intensity control in this model. It may be that the delayed signal is to be brighter to give contrast.

Mark


SCMenasian
 

Barry,

Maybe the discussion of Aux Z axis Control and Aux Z Axis Out on pages 3-16 and 3-17 of the 7B53A manual will give a clue. It describes the Z-Axis interface to the mainframe. Since the 7B92A has a front panel contrast adjustment, the interface probably has the ability to control intensity via a voltage level. Perhaps a bad component in those sections of your 7B53A has that level pegged.

Stephen Menasian


n4buq
 

Stephen,

I'll have to check that. I think the problem is seen for other time-bases so not sure if it's a problem with the plugin but it could be.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "SCMenasian" <scm@menasians.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, October 21, 2021 11:04:37 AM
Subject: Re: [TekScopes] 7704A - Delayed Sweep Intensity Too Bright
Barry,

Maybe the discussion of Aux Z axis Control and Aux Z Axis Out on pages 3-16 and
3-17 of the 7B53A manual will give a clue. It describes the Z-Axis interface to
the mainframe. Since the 7B92A has a front panel contrast adjustment, the
interface probably has the ability to control intensity via a voltage level.
Perhaps a bad component in those sections of your 7B53A has that level pegged.

Stephen Menasian



n4buq
 

Mark,

Yes, I believe the intent is to "highlight" part of the trace; however, mine is highlighting much to bright. I'll have to check those voltage levels in the Z-Axis circuit and see if the plugins are somehow providing the wrong voltages.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, October 21, 2021 10:17:14 AM
Subject: Re: [TekScopes] 7704A - Delayed Sweep Intensity Too Bright
Barry,

See if having the A/B intensity turned up and the crt bias up (more negative at
the grid) helps. If your S/N is <210000, check Q320, Q322, Q420 and Q422. These
are in the two heatsinks on the right side top. If these are leaky, use
KSP10BU. I do not see any internal intensity control in this model. It may be
that the delayed signal is to be brighter to give contrast.

Mark



SCMenasian
 

Barry,
If it's that way with several plugins, it might be in hte receiving side of that interface in the 7704A.

Stephen