1084 Monitor with Red Screen

Dipski · 07 July 2018, 02:17

I've got a 1084 monitor that was working well but had a chipped and scratched CRT - I swapped in a CRT from another working 1084 but it is giving a red background screen with some horizontal lines running through it.

Thinking it would be a flaky solder joint that came loose when getting the boards in and out I resoldered all of the joints on the yoke PCB but there was no change.

The picture does display ok, and has all of the colours present - though with that red colour as the background.

Any ideas on what might be going on?

Jope · 07 July 2018, 08:26

Red gun stuck on. Perhaps some gunk inside the tube has fallen into the electron gun and is now shorting it. Unless you had one of the transistors for driving the red gun fail on the chassis or neck board at the same time as you did the tube swap.

Check the transistors first, working back from the red gun. Perhaps desolder the one that is immediately driving the gun and switch on the monitor again. If your red raster is still present, then the problem is your tube.

Hewitson · 07 July 2018, 19:19

If the gun was stuck on wouldn't the red be more prominent? Checking the transistors is certainly good advice.

Backing off the screen pot on the flyback should remove the retrace lines.

Jope · 09 July 2018, 16:57

That's how they are when the gun is constantly firing, red raster + visible retrace lines.

07 July 2018, 02:17	#1
Dipski Registered User Join Date: Jun 2016 Location: Victoria, Australia Posts: 32	1084 Monitor with Red Screen I've got a 1084 monitor that was working well but had a chipped and scratched CRT - I swapped in a CRT from another working 1084 but it is giving a red background screen with some horizontal lines running through it. Thinking it would be a flaky solder joint that came loose when getting the boards in and out I resoldered all of the joints on the yoke PCB but there was no change. The picture does display ok, and has all of the colours present - though with that red colour as the background. Any ideas on what might be going on? Attached Thumbnails

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07 July 2018, 08:26	#2
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,864	Red gun stuck on. Perhaps some gunk inside the tube has fallen into the electron gun and is now shorting it. Unless you had one of the transistors for driving the red gun fail on the chassis or neck board at the same time as you did the tube swap. Check the transistors first, working back from the red gun. Perhaps desolder the one that is immediately driving the gun and switch on the monitor again. If your red raster is still present, then the problem is your tube.

07 July 2018, 19:19	#3
Hewitson Registered User Join Date: Feb 2007 Location: Melbourne, Australia Age: 41 Posts: 3,773	If the gun was stuck on wouldn't the red be more prominent? Checking the transistors is certainly good advice. Backing off the screen pot on the flyback should remove the retrace lines.

09 July 2018, 16:57	#4
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,864	That's how they are when the gun is constantly firing, red raster + visible retrace lines.

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