Topics

B92A no sweep


brentleew2003@...
 

I forgot to mention that, initially last week the problem began with the sweep working fine for the first 30 seconds and then quit. It might come back for a few moments, even another 30 seconds on occasion before not working at all: I assumed from a component warming up. This week however it has not worked at all. I was able to use a thermal camera to look at heat on the boards and found nothing unusual.Whatever it is, it isn't intermittent any longer.


 

On Tue, 14 Feb 2017 04:01:49 +0000 (UTC), you wrote:

Thanks David,I have re-seated everything I could find, I am using an extender I just built from John Griessen.
That is going to make things a lot easier.

Cam switches are all in good shape and properly functioning.
I didn't know if there were any known issues with the 7b92a.
There are no special issues that I know of.

From what I can read, they seem pretty reliable.
They are pretty complex though. The problems I have seen are shorted
tantalums and mechanical problems with the cam switches.

I know there is some mention of the sweep generator 155-049-02, but I am not sure how to diagnose it's proper function or if it's even suspect.

Thanks for the thoughtsBrent
On 14 Feb 2017 04:16:50 +0000, you wrote:

I forgot to mention that, initially last week the problem began with the sweep working fine for the first 30 seconds and then quit. It might come back for a few moments, even another 30 seconds on occasion before not working at all: I assumed from a component warming up. This week however it has not worked at all. I was able to use a thermal camera to look at heat on the boards and found nothing unusual.Whatever it is, it isn't intermittent any longer.
The problem before the unblanking was lost might simply have been the
sweep signal getting lost between the output of the sweep generator
and the horizontal amplifier. The alternatives are much more complex.

I had an idea which might apply to before the sweep vanished; if the
sweep was being displayed as a dot which gets wider as the sweep speed
is increased, then the unblanking is working and probably the sweep
integrator is working. The odd part is that the sweep reset was
apparently also working even though the sweep was never reaching that
point and to me that points to a problem with the end of sweep
comparator continuously indicating the end of the sweep.

The good news, if it can be considered that, is that the sweep
generators are all discrete. The bad news is that the loss of
unblanking (and loss of triggering?) indicates a larger problem.

Before getting too involved going through the circuits, I would make
measurements of the supply voltages on the boards. Maybe one of the
power supply decoupling networks gradually failed.


 

Hi Brent,
To get an intermittent to act up I reach for two things. I grab a can of
freeze spray, and a hair dryer. Use the hair dryer to warm up the entire
plugin. Do not use a Hot Air Gun - it gets too hot.

The freeze spray allows you to focus tighter on individual ICs or on small
areas of the PC board. More often than not the heat or the cold will trigger
an intermittent back to life.

Dennis Tillman W7PF

-----Original Message-----
Sent: Monday, February 13, 2017 8:17 PM
Subject: [TekScopes] B92A no sweep

I forgot to mention that, initially last week the problem began with the
sweep working fine for the first 30 seconds and then quit. It might come
back for a few moments, even another 30 seconds on occasion before not
working at all: I assumed from a component warming up. This week however it
has not worked at all. I was able to use a thermal camera to look at heat on
the boards and found nothing unusual.Whatever it is, it isn't intermittent
any longer.
------------------------------------
Posted by: brentleew2003@...
------------------------------------


Brent Watson <brentleew2003@...>
 

Thanks Dennis,I did try the freeze spray, I though I had a result but then chalked it up to random, intermittent activity.I did try my heat gun attached to my reflow station and kept it all quite tame. Neither gave the response I was hoping. But I did run out of freeze spray before I could reach any solid conclusions, and I did not have the extender at that point. I thought I had a reaction to cold on the back ( covered by the sweep logic board) half of the interface board (B069999 and up) possibly Q902, Q912 or Q900, Q910. But I pulled and checked them and they test out OK.I will keep digging: the logic is thick though.

From: "'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Tuesday, February 14, 2017 9:03 AM
Subject: RE: [TekScopes] B92A no sweep

  Hi Brent,
To get an intermittent to act up I reach for two things. I grab a can of
freeze spray, and a hair dryer. Use the hair dryer to warm up the entire
plugin. Do not use a Hot Air Gun - it gets too hot.

The freeze spray allows you to focus tighter on individual ICs or on small
areas of the PC board. More often than not the heat or the cold will trigger
an intermittent back to life.

Dennis Tillman W7PF

-----Original Message-----
Sent: Monday, February 13, 2017 8:17 PM
Subject: [TekScopes] B92A no sweep

I forgot to mention that, initially last week the problem began with the
sweep working fine for the first 30 seconds and then quit. It might come
back for a few moments, even another 30 seconds on occasion before not
working at all: I assumed from a component warming up. This week however it
has not worked at all. I was able to use a thermal camera to look at heat on
the boards and found nothing unusual.Whatever it is, it isn't intermittent
any longer.
------------------------------------
Posted by: brentleew2003@...
------------------------------------

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[Non-text portions of this message have been removed]


Joseph Tatum
 

On the 2465 I just got going, heating the board with a hair drier worked to make it start working right. But freezing would not make it act up. Had to heat the MUX with a soldering iron to isolate the problem.

When you do need freeze spray and do not have easy access to it; get a can of compressed air that is used to blow dust from computers. You can turn it upside down and get the same effect as the freeze spray.

I once had a problem with a computer monitor that would come on when heated. I put a wire wound resister on the end of a dowel and connected it to a 12 v supply. I used that to reach into its innards and isolate a small cap that was causing the problem.

Probably none of the is news to most on here, but it might help sombody. Hope so anyway.


brentleew2003@yahoo.com <brentleew2003@...>
 

I like the power resistor/heater plan. Very area specific, too. 
Happy Connecting. Sent from my Sprint Phone.

------ Original message------From: tatumj1@... [TekScopes] Date: Tue, Feb 14, 2017 10:11To: TekScopes@...;Subject:RE: [TekScopes] B92A no sweep
  On the 2465 I just got going, heating the board with a hair drier worked to make it start working right. But freezing would not make it act up. Had to heat the MUX with a soldering iron to isolate the problem.

When you do need freeze spray and do not have easy access to it; get a can of compressed air that is used to blow dust from computers. You can turn it upside down and get the same effect as the freeze spray.

I once had a problem with a computer monitor that would come on when heated. I put a wire wound resister on the end of a dowel and connected it to a 12 v supply. I used that to reach into its innards and isolate a small cap that was causing the problem.

Probably none of the is news to most on here, but it might help sombody. Hope so anyway.

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


brentleew2003@yahoo.com <brentleew2003@...>
 

I wonder if you recall what kind of cap that was that you found with the resista-heater. I only think of electrolytics being subject to age. But I imagine others could fail as well.
Happy Connecting. Sent from my Sprint Phone.

------ Original message------From: tatumj1@... [TekScopes] Date: Tue, Feb 14, 2017 10:11To: TekScopes@...;Subject:RE: [TekScopes] B92A no sweep
  On the 2465 I just got going, heating the board with a hair drier worked to make it start working right. But freezing would not make it act up. Had to heat the MUX with a soldering iron to isolate the problem.

When you do need freeze spray and do not have easy access to it; get a can of compressed air that is used to blow dust from computers. You can turn it upside down and get the same effect as the freeze spray.

I once had a problem with a computer monitor that would come on when heated. I put a wire wound resister on the end of a dowel and connected it to a 12 v supply. I used that to reach into its innards and isolate a small cap that was causing the problem.

Probably none of the is news to most on here, but it might help sombody. Hope so anyway.

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Joseph Tatum
 

It was a small mylar cap. The ones that are cased in clear plastic. They look silver as you can see the foil inside. I doubt it would work on an electrolytic. I do not remember ever making anything work by heating an electrolytic. I suppose it could, maybe does, happen. I remember trying to heat the exposed metal on some but do not remember that it ever helped.


 

Generally speaking these are very reliable, and have very low leakage if
this is the one I am thinking of. That is important for a linear ramp.

Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, February 14, 2017 3:37 PM
Subject: Re: [TekScopes] B92A no sweep

It was a small mylar cap. The ones that are cased in clear plastic. They
look silver as you can see the foil inside. I doubt it would work on an
electrolytic. I do not remember ever making anything work by heating an
electrolytic. I suppose it could, maybe does, happen. I remember trying to
heat the exposed metal on some but do not remember that it ever helped.
------------------------------------
Posted by: tatumj1@...
------------------------------------


Joseph Tatum
 

You are right. I don't ever remember finding another one bad. That one was in an old CRT type computer monitor I bought at Fort Rucker Alabama DOD sale.


Brent Watson <brentleew2003@...>
 

Apparently electrolytic's aren't the only cap that can fail.

From: "tatumj1@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Tuesday, February 14, 2017 3:36 PM
Subject: Re: [TekScopes] B92A no sweep

  It was a small mylar cap. The ones that are cased in clear plastic. They look silver as you can see the foil inside. I doubt it would work on an electrolytic. I do not remember ever making anything work by heating an electrolytic. I suppose it could, maybe does, happen. I remember trying to heat the exposed metal on some but do not remember that it ever helped.

[Non-text portions of this message have been removed]

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Brent Watson <brentleew2003@...>
 

But fail very rarely


From: "Brent Watson brentleew2003@... [TekScopes]" <TekScopes@...>
To: "TekScopes@..." <TekScopes@...>
Sent: Tuesday, February 14, 2017 7:40 PM
Subject: Re: [TekScopes] B92A no sweep

  Apparently electrolytic's aren't the only cap that can fail.

From: "tatumj1@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Tuesday, February 14, 2017 3:36 PM
Subject: Re: [TekScopes] B92A no sweep

  It was a small mylar cap. The ones that are cased in clear plastic. They look silver as you can see the foil inside. I doubt it would work on an electrolytic. I do not remember ever making anything work by heating an electrolytic. I suppose it could, maybe does, happen. I remember trying to heat the exposed metal on some but do not remember that it ever helped.

[Non-text portions of this message have been removed]

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[Non-text portions of this message have been removed]


 

Everything, even a humble piece of solid wire, has failure mechanisms. Humans have lots of them. Stars have them on a longer scale. The fundamental particles in the universe have failure mechanisms too and eventually decay although the timescale for those is hundreds of orders of magnitude longer. It is all just a matter of time and of failure rates.

Good engineering involves balancing things like failure rates, costs, space constraints, manpower, parts availability, repairability, usability, uniqueness, etc.

Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, February 14, 2017 7:41 PM
Subject: Re: [TekScopes] B92A no sweep

Apparently electrolytic's aren't the only cap that can fail.

From: "tatumj1@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Tuesday, February 14, 2017 3:36 PM
Subject: Re: [TekScopes] B92A no sweep

It was a small mylar cap. The ones that are cased in clear plastic. They look silver as you can see the foil inside. I doubt it would work on an electrolytic. I do not remember ever making anything work by heating an electrolytic. I suppose it could, maybe does, happen. I remember trying to heat the exposed metal on some but do not remember that it ever helped.

------------------------------------
Posted by: Brent Watson <brentleew2003@...>
------------------------------------


Michael A. Terrell
 

That sounds more like a polystyrene capacitor.

-----Original Message-----
From: "tatumj1@... [TekScopes]" <TekScopes@...>
Sent: Feb 14, 2017 6:36 PM
To: TekScopes@...
Subject: Re: [TekScopes] B92A no sweep

It was a small mylar cap. The ones that are cased in clear plastic. They look silver as you can see the foil inside. I doubt it would work on an electrolytic. I do not remember ever making anything work by heating an electrolytic. I suppose it could, maybe does, happen. I remember trying to heat the exposed metal on some but do not remember that it ever helped.



Michael A. Terrell


Joseph Tatum
 

You are right. I was not satisfied with the term mylar when I typed it. The description I gave fits a polystyrene cap but I did have the name wrong. But that is what it was.