Apple //c slow wave display

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Apple //c slow wave display

New topic as I continue to troubleshoot my old Apple //c and try to bring it back to life.

Now that it boots (yay!, thanks for the help from this forum), the display has a slow "wave" left-to-right that moves up from the bottom to top.   It is not the monitor.  I switched out the little //c monitor for a Apple Color Composite monitor.   Same symptom.

It repeats about every 15 seconds or so... starting from the bottom, slowly progressing up to the top, in curved grouping about the 1" in size like someone is taking a hold of the edge and pulling it left very smoothly.   Again, NOT the monitor as I've tested on two different monitors with same result.

Thanks for any ideas.

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60hz hum

Sounds like to me that the IIc is getting some 60hz AC from the power adapter. Is the adapter you are using the OEM Apple "Brick on a Leash"? Or is it the ebay Switching Mode power supply one. If you have a good quality meter you should be able to probe the connector on the power supply and mesure the AC ripple coming out of it. You should also see the ripple coming out of the internal regulator box. You really should not have any more than 150mV (miliVolts) ripple coming out of either the regulator or the power supply, thats a rough number, but any AC is not good to have in the computer. I will check mine In a moment and give you the numbers I have from my OEM one.

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Could be a bad video

Could be a bad video connection (try wiggling and turning the video cable at the computer. Also make sure there is nothing within a foot anywhere around the monitor just to rule out interference from things (like other monitors).

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Apple OEM
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Meter readings

@Pinkyboy1006, thanks for the readings.  I have only had simple multimeter and get very near same output voltage on OEM brick power supplies (I have two, both read same).   I have also checked the reading after the power supply inside the case, and get the following at J1: Pins 6,8=-11.53v,Pins 14-26=16.96v (input voltage), Pins 28-34=5.07v, Pins 36-40=12.3v. (all EVEN Pins of course).

YESTERDAY I took delivery of a Rigol DS1054Z and a Tripplite IS500HG Isolation Transformer from Amazon.  (EEVLOG gave me confidence to make this purchase) and hope to be learning this weekend how to measure the ripple.

 

I will report back once I check all the suggestions here, and report values once I learn how to take them with the scope.

 

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Additional video information

So I took the suggestion to check the video cable as well as the proximity of other monitors. 

 

1) I disconnected the composite video from the Apple Color Composite monitor completely.

2) I hooked up my //gs  RGB monitor.   Result.  Bright blue screen with thin black lines about 1 inch apart vertically.

3) I hooked up composite again AT THE SAME TIME as RGB, and the composite display was completely wonky.  Not displaying text and flashing etc.

4) Unplugged the RGB cable, leaving composite connected, and the composite screen went back to normal text!  (still with slow wave tho')

 

Does this description help anyone recognize what this might be?   Power problem?  Bad graphics/video chip?

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“RGB”

so that connector looks like a standard apple RGB connector but it is not. So try not to plug the monitor in again, if I remember right one of the video pins on the iigs monitor goes to +5 volts if you connect it to a iic. You are lucky that the iic recovered from that. Anyway if you use the ac measurement on your meter on the pins you already  mesured with DC you should ONLY get maybe at max 100mV AC. When I get home from work today I will open my iic and measure my regulator box to compare to yours.

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Voltages

I measuerd at the J11 connector with my simple multimeter set to AC~V and got these:

Pins 6-8 = 0.018

Pins 14-22 = 0.065

Pins 28-34 = 0.003

Pins 36-40 = 0.006

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all fine

all of those voltages seem ok. There is one more thing i can think of that I should have thought of before. The video connector. While you still have it open, try turning the barrel of it, if it turns easliy solder the barrel on the back side and see if that fixes it.

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