577 D2 Display Issues


@gmilliorn
 

I've been trying to restore a 577 D2 that had several problems. The
previous owner(s) hacked up the -12V supply and the regulator was floating,
unheatsinked. The 200V fuse was blown (cautiously replaced, no issues
so far), sticky switches (cleaned), excessive ripple (recapped). After
all that I got the stairstepper working and get the mostly correct display.

There's a few odd issues though:
* Every 1-5 seconds there's a brightness flash on the traces. There's
nothing seen on power supplies or main boards that correlates.
* Focus is sharp but intensity ranges from low-high-low.
* HV is limited to -3362V max (or min?), but should range -3270..-3570.
* There's black soot on the inside of the HV shield as well as the back
of the yoke connector (I can see someone's thumbprint). Not sure
how that happened, but it was in two physically separated areas.

So it mostly looks like an HV issue, but that odd flash makes me worry
it could be the tube. It doesn't appear to have been replaced, despite
the thumbprint. Does any of the above point to one or the other?

Thanks,
Gary


Mark Vincent
 

Gary,

Clean the black soot out of everywhere. You will likely have to remove the tube because of the good chance it is also dirty on the tube, socket and inside the shield. The flashing could be the soot being conductive at higher voltages and arcing over.

Mark


Ed Breya
 

Is this the storage version? I always forget which is which. If it's the storage type, you should always do troubleshooting first in non-store, where things are less complicated. The occasional flashing could be some sort of automatic erasing/updating going on in storage mode.

These also have an automatic intensity reduction function that cuts it down when the collector voltage sweep is small, like around 2 divs p-p or less, to help prevent screen burn. Something flakey in that section may cause odd behavior.

Ed


Andy Warner
 

If the intensity low-high-low thing persists after you clean the soot off,
you may have a weak tube. I assume this is as you move the intensity
control clockwise.

Look for a 5110 scope, they have the same tube, with the telltale graticule
arrows in the lower left corner. I was in the same boat as you a few months
ago, but was able to find a 5110 with a good tube, so do not lose hope.

On Mon, Sep 13, 2021 at 15:07 <gmilliorn@gmail.com> wrote:

I've been trying to restore a 577 D2 that had several problems. The
previous owner(s) hacked up the -12V supply and the regulator was floating,
unheatsinked. The 200V fuse was blown (cautiously replaced, no issues
so far), sticky switches (cleaned), excessive ripple (recapped). After
all that I got the stairstepper working and get the mostly correct display.

There's a few odd issues though:
* Every 1-5 seconds there's a brightness flash on the traces. There's
nothing seen on power supplies or main boards that correlates.
* Focus is sharp but intensity ranges from low-high-low.
* HV is limited to -3362V max (or min?), but should range -3270..-3570.
* There's black soot on the inside of the HV shield as well as the back
of the yoke connector (I can see someone's thumbprint). Not sure
how that happened, but it was in two physically separated areas.

So it mostly looks like an HV issue, but that odd flash makes me worry
it could be the tube. It doesn't appear to have been replaced, despite
the thumbprint. Does any of the above point to one or the other?

Thanks,
Gary





--
Andy


@gmilliorn
 

Thanks for the suggestions everyone, I will start with cleaning the soot.

Is this the storage version?
The D2 is the non-storage. The front-panel intensity pot is very linear, delivering -30..30V to
the HV board. But the intensity range trimmer under the shield is hard to turn and acts oddly,
I wonder if it is contaminated with soot just like everything else there.

I hadn't thought of soot as conductive, though I guess that's obvious in hindsight. The HV adjust
is also in the sooty area, and HV range is also not working.


@gmilliorn
 

While cleaning soot off of everything, I pulled the CRT connector off the back and an
orange plastic segment crumbled to dust. The connector still has a visible key but the CRT
doesn't, so I guess that was the pin 1 indicator. The tube now only has a white silicone
coating and center post.

I reassembled it (fortunately I took a picture) and it works about the same as before. This
time I could hear a high whine. I can see sparks on the intensity pot when I turn it. The
neon lamps fire if I turn it too low.

I guess this soot is all over the pots (they are open frame) and they all
need to be replaced.


@gmilliorn
 

Cleaning the contamination everywhere, and replacing the pots in the 577 HV
driver did not fix the display, so I managed to get a rackmount 5110 at auction.
It has a crisp stable display.

Looking inside, I see that the display half is nearly literally the top half of the 577 D2,
just as Andy mentioned. The only differences I see are the calibrator loop and that the
connections to the HV board are directly wired instead of pin connectors (cost savings,
I guess).

Given the soot that was all over my HV board, I'm inclined to perhaps just transplant
the tube and the board. The schematics seem identical, unless I'm missing something
I'd only have to convert the cables to connector pins. Has anyone tried that as well?


Zentronics42@...
 

I can confirm that the tube is a direct transplant however I do not know about the HV board. I used a 5110 to replace in the tube in one of my 577's no modification needed.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of gmilliorn@gmail.com
Sent: Thursday, October 14, 2021 9:25 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577 D2 Display Issues

Cleaning the contamination everywhere, and replacing the pots in the 577 HV driver did not fix the display, so I managed to get a rackmount 5110 at auction.
It has a crisp stable display.

Looking inside, I see that the display half is nearly literally the top half of the 577 D2, just as Andy mentioned. The only differences I see are the calibrator loop and that the connections to the HV board are directly wired instead of pin connectors (cost savings, I guess).

Given the soot that was all over my HV board, I'm inclined to perhaps just transplant the tube and the board. The schematics seem identical, unless I'm missing something I'd only have to convert the cables to connector pins. Has anyone tried that as well?


@gmilliorn
 

Any advice on getting the tube out? I assumed if I removed the top and bottom rubber gaskets from
the front panel it would slide out fairly easily, but it is fighting me so far. The gaskets appear to be glued in.
The rear clamp is loosened, but removing the three pads around the neck back there seems riskier than
trying from the front.