Apple IIc display lines

[mbaran]

Can anyone help me diagnose this? I've also xposted it to applefritter. 

In this linked photo you can see a rolling "interference" through the display.

This only occurs when the //c is on, but not while just the Monitor //c is on.

It does appear to be more shaky and will distort the text characters on floppy read/write.

Is there a filter/capacitor/component that is responsible for this type of effect that I could replace?

Thanks!

 

[Timbo]

I had some display problems with my Apple II and using a different cable fixed it- might be worth trying?

 

[mbaran]

I've tried two different ones, neither is better than the other. 

As a test I removed the logic board and connected the two wires to the two connectors of the RCA pins on the board, just to make sure the connector itself wasn't tarnished or damaged. Same result. 

 

[Elfen]

That's a few but simple things to fix. Its mostly your video connection and not obtaining a proper ground.

1) Replace your video cable with a short (3ft or less)  RCA to RCA Video Cable. Some people use RCA to RCA Speaker cables and think that it will work and for the most part they do but the longer the wire the more susceptible it will be to picking up stray magnetic noise which will show up on the monitor. Also, the speaker wire is not ground shielded properly like a video cable.

2) clean the RCA Video ports on both the Apple IIc and the Monitor. A very fine Emory Cloth would be best, wrap it around the outside the jack and twist it a few times around to remove the oxidation on both ports.

3) move the Apple IIc's Power Pac away from the system as far as you can place it. It produced a lot of magnetic noise that a monitor and video cable can pick up.

These three alone should fix most video problems with the Apple IIc.

 

[mbaran]

Thanks, I will try a better (and shorter) cable. The two I've tested with are either very thin, or very long. 

As far as the power pack goes, I am using an after market one provided by Dr. Ken B. I wonder if this pack emits more EMI than the OEM one might have? I will route the cables so that it is as far away as possible. 

Does something like http://www.monoprice.com/Product?c_id=102&cp_id=10241&cs_id=1024101&p_id=6026&seq=1&format=2 look beefy enough? I will just cut the band and separate the video from the two stereo cables. 

Or is there some benefit to using the original apple cables such as these http://www.blujay.com/item/Apple-Color-Composite-Video-Cables-for-Apple-II-IIe-IIc-IIGS-Macintosh-Computers-9010400-4096171

 

[mbaran]

So more testing reveals that these rolling lines or "video hum" only appear on the Monitor //c. 

Wonder what could be going on inside there...

 

[TheWhiteFalcon]

You need to feed the little Woz inside the IWM.

 

[Elfen]

I would not cut the video cable to separate them. But it looks like  great buy for less than $2. The Apple cable is great but not at 5 - 10X the price of the regular cable.

If the line is coming from the monitor alone looks like either a shield is missing inside or bad caps/broken solder joints on the board. You can go in and desolder the bad looking joints and then resolder them. Look for burnt connectors and swollen caps inside the board.

The third party power supply has me worried, as it could be sending in stray signals. Better to get an Apple IIc power pack or a Laser 128/Laser XT power pac. The Laser power pac is more beefier than the Apple one.

 

[mbaran]

So 1 more correction, I hooked up the "monitor" to a small media player I have, since it's just an NTSC compatible display device. Works flawlessly. 

I can then narrow it down to two things. Either it needs a seriously shielded cable, which I will test tomorrow when it arrives -OR- that Dr Ken B power adapter uses some kind of floating ground (not from the wall) and there's a ground loop.

The odd thing is that my small media player does not seem to have a ground prong, so surely those run off different grounds. 

We shall see tomorrow. 

 

[Elfen]

Good luck with that. I'm suspecting the D. Ken PSU. You can run the IIc off a small motorcycle or burglar alarm system lead-gel cell battery, it runs off 12V to 15V as I remember. The IIc uses a 65C02 which can as low as 3.5V as some of the other CMOS Chips as well. Its the ports and disk drive requires the higher voltages. But being CMOS, stray signals can go right through them.

Look over this you-tube vid on how this guy did it.

 

[techknight]

Power supply is putting out too much noise. You need the correct linear supply for this thing.

 

[mbaran]

Well, I did speak with Ken B and he has sold nearly 100 of these with no issues. 

That being said, my new cable came today and works perfect. It seems that the IIc simply is noisy and requires a well shielded cable.

 

[Elfen]

Great to hear on the success.

Has that IIc been taken apart by you? To reduce heating in the past, some owners went in and removed the RF shielding.

 

[mbaran]

I've taken it apart many times, but I'm not sure which RF shielding you're talking about? It may have previously been removed, depending on where it was...

 

[Elfen]

When you remove the back from the monitor, there is supposed to be a metal box that covers most of the electronics. But like I said, they mostly are removed long ago as it was a bad design that made them heat up.

 

[mbaran]

I think that giant hunk of aluminum is actually still in that monitor //c. 

There's some components bolted to it though, so I'd have to tie them up somewhere to remove that piece. I'll take a look over the weekend.