Florescent Desk Lamp-Causing Traveling Vertical line-Classic

[uniserver]

So i am here tearing into this Macintosh Classic.

Pulled out the A/B board, Had to re-cap it, Screen was wavy, HD would not spin etc. etc.

Anyways, Replaced all the caps following my recent post. viewtopic.php?f=7&t=21471

And, Everything now works great!! HD fires right up!

Screen is Solid and Bright.

Only now there is this line. Basically after a few hours of Probing... testing...

I had a hunch that the issue might be caused by external interference.

Whenever I test Compact macs, I always test them with the rear can off.

So I put it all back together, tightened the screws up.

Then fired it back up.

And sure enough this " traveling line " syndrome I was experiencing had went away.

(The line was slight and it would travel from top to bottom of the screen all the way across).

Kind of irritating, because I wasted about 2 hours trying to track this issue down.

At-least it works now.

 

[Trash80toHP_Mini]

That's exactly what happens to CRTs sitting next to/near the Macintosh Portrait Display/RFI Generation Unit.

 

[uniserver]

Really? So you've seen this behavior before?

 

[Trash80toHP_Mini]

Yep, you can't see it in the picture, because of the glare hood, but there was a piece of 18ga. galvanized steel in between the Portrait and the Radius 21" CRT. I was going to ground it, but the grayish horizontal line, rolling bottom to top :?: went away without needing to ground it, but I did so anyway, IIRC.

 

[uniserver]

is that a q605 driving 2 monitors?

what os is on the bad boy, cool custom desk.

you are hard core!

 

[Trash80toHP_Mini]

The Q605 runs 7.5.5 and might or might not have been online at that point. The 2300c/DuoDock MoBo video ran the Portrait and was on all the time. I wouldn't have had issues with the rolling lines on the other CRT for 605 playtime because the Portrait would have been powered down

The Digital Audio, 2300c/DuoDock/Macintosh Display Card 24x, and 6360/G3 were permanently KVM'd to the Radius21.The production/bookkeeping/plotter server setup was always on the switch. I'd swap the 605 out with the 475 at times, but mostly I used the 605 to bring the portrait up to level with the 21 incher on the KVM switch.

Thanks, that was my favorite workstation ever. The fourth Mac on the switch was usually on the backside of the triangular desk. I rotated the playtime Macs on the fourth position on the KVM switch. The side against the wall was intended to be a Gaming PC for my Flight Sim collection, but I never did get that together. The desk was on wheels. The gray, pipe looking thing hanging down was an umbilical carrying AC, Network, and serial connections from a lighting/utilities track above.

The carcass of the desk was a shelf unit holding the 6360/G3 and DuoDock. The main filing drawers were parallel to it, but pivoted to give access to all four sides of the carcass/rack. The desktop was clear Plexi with a frame directly under that Big@$$ CRT. It extended well over the cheap chest of drawers I found, it made a great credenza. You can just barely see the glare off the handle of the G-4 sitting on the floor between the backside of the carcass and credenza. That was supposed to pivot away from the backside of the carcass for access as well, but I never got around to building it.

 

[Gorgonops]

Really? So you've seen this behavior before?

What you saw isn't unusual at all; I used to see it on black-and-white TVs/monitors all the time 20 years ago. (For some reason color monitors seem more immune to it, or at least the symptoms tend to be more subtle.) The line is a burst of interference from the ballast of the fluorescent lamp hitting the monitor every 1/60th of a second, and it moves vertically across the screen because the line frequency of the utility's AC power isn't *quite* in sync with the screen refresh frequency of your monitor. As Trash notes you could get the same thing from setting two poorly shielded CRT monitors close to each other; in that case the interference is usually from close-but-still-mismatched vertical sync pulses.

This used to be a serious problem in offices that had the old eye-killing 60hz florescent ballasts. Most buildings use higher frequency ballasts these days but you still find the old-fashioned ones in small desk and utility lamps.

 

[James1095]

It's known as a "hum bar" and indeed is very common with CRT displays. I've run into it frequently with vintage arcade games when bad connections develop and you end up with 60Hz hum riding on the video and sync lines to the monitor. It's much of the reason why analog television vertical refresh rates usually match the power line frequency of the region. Syncing the vertical refresh to the line frequency minimizes the effect of interference.