Re: Weird lines down the display

[Alistair J Ross <mail@ataliross.co.uk>]

On Thu, 16 Sep 2004 09:10:06 +1000, David Wilson wrote:

> Do you have 40 one pixel wide lines spaced at 7 pixel intervals?
> If so I would check the chargen (reseat the IC as one of the output
> pins may not be making a good contact with the IC socket) and the
> parallel to serial chip (74166) [reseat it as well] as these are the
> only two chips that have the text video data in parallel form.

David, how accurate you are!

I had a quick squint at the Apple II reference manual and noted 
that the 74166 was indeed something to look at.

On prizing it out of its slot i noted that it was corroded quite
badly on one pin only. A gentle rub later, a reseating and all was
dandy.

I didn't believe all of this 'skootching' business up untill now
because I have 3 dead Apples on my hands at present, but this
sure did fix this one ;)

Thanks guys!

Alistair Ross

> Alistair J Ross <mail@ataliross.co.uk> writes:
>>  I have obtained a EuroPlus mainboard in working order. I don't recall
>>touching the mainboard and causing any damage, but now when it starts up,
>>I get straight lines down the screen in text mode. I can still see the
>>text on the screen but the text remains. The machine seems to be working
>>fine otherwise. If I switch it to graphics mode with 'GR' - the lines
>>dissappear apart from the text area at the bottom of the screen.
> 
> Do you have 40 one pixel wide lines spaced at 7 pixel intervals?
> If so I would check the chargen (reseat the IC as one of the output
> pins may not be making a good contact with the IC socket) and the
> parallel to serial chip (74166) [reseat it as well] as these are the
> only two chips that have the text video data in parallel form.
> 
>>Is this a faulty display ROM or could it be a problem with the monitor?
> 
> Possible (ROM) and extremely unlikely (monitor) as you say the lines go
> away in GR mode - the monitor is just displaying dots - it cannot tell
> if they are text dots or graphic dots...
> 
>>Why would the problem not initially show it's self and then show now?
> 
> Failures have to happen sometime :-(
> 
>>Anyone seen a problem like this before?
> 
> No.
> 
>>PS: Where is the video rom on a EuroPlus?
> 
> Same place as on a US II+. Location A5 according to the Red Book (next to
> the keyboard socket). I don't recall it being moved in later revs of the
> motherboard. It should be labeled on the motherboard - 2513 if pre rev 7,
> CHARGEN if rev 7 or later (this is from memory so I could be wrong). Anyway,
> it is a 24 pin IC that is not one of the D0 through F8 ROMs.

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-----------------------------------------------------------[ Alistair J Ross]--
Alistair Ross
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