Apple II Europlus : no boot, screen pattern garbage

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Apple II Europlus : no boot, screen pattern garbage

Hello everyone

 

I've solved my first problem on this Apple II Europlus i'm trying to repair ; it used to have a 14Mhz clock (!)

Changing a 74S in the clock generatin made it 1Mhz again, it tok a while to figure to right one as this was not the most obvious one (linked to phase 0) but another one, the 4 bit counter.

 

NOw I have some (pal) video output ; garbage. :(  I've read all topics on this forum about this kind of issue before posting :) Some points to broken links, which does not help.

My display shows a pattern of blocks of  vertical lines, looking a bit like 7 position dip switches one next to the other

https://ibb.co/KqZgHn2

 

No beep

 

I get the exact same pattern if I remove the CPU

 

So something is very wrong ; basically the PAL generation works, but the CPU doesn't even start or cares.

I cleaned the whole motherboard, reseated multiple times all I could think of.

 

I'm not much experienced in Apple repairs, and would appreciate some pointers about where to sart in such case

I do have an electronics lab so I can make measures if needed.

 

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https://commodore.bombjack

https://commodore.bombjack.org/apple/apple-books.htm

 

 

I'd recommand starting with the "How to Repair and Maintain your Apple Computer" book you can find the PDF for on that link.

 

You may also find some of the other books like the Sam's Computerfacts and Apple Technical Procedures books useful.

 

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This PDF basically says that

This PDF basically says that if my motherboard is bad I should get it to a technician :)

 

 

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That other book from your

That other book from your link

The_Apple-II_Circuit_Description

Looks more like the kind of info that I can do something with

 

I'll first check all the clocks, as this is obviously something that was broken in mine.

 

I would rreally appreciate of people having the same kind of problems (an aple II that doesn't even start the cpu and has a video output) would share their debug process... As you're really left in the dark when the computer does not boot at all

 

 

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Could be lots of things, but

Could be lots of things, but most proabaly a RAM issue. Unless you want to spring for something like the ROMXe which can diagnose RAM even when the computer won't boot, your next step should be to swap RAM chips from the upper banks into the lowest one until it boots.

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Sorry, the Sams book "Apple

Sorry, the Sams book "Apple II Plus IIe Troubleshooting & Repair Guide" might be better than the other one I mentioned.  It acutally has a chip level trouble shooting guide.  It's been a while since I've needed to do that.

 

 

 

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