Apple II Europlus, vertical white bars on screen

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Apple II Europlus, vertical white bars on screen

Hi all :)

 

First post - I have had an Apple II Plus (Europlus actually, I'm in the UK) in my loft for more years than I care to remember, and recently I've decided I am going to get it working, as well as some other 'vintage' computers such as a couple of C64s, VIC20s, Amigas, BBC Model Bs, etc. 

 

It's never worked for me. It was given to me a long time ago because it was faulty, but I can't remember what it was doing/showing on screen at that time. When I first plugged it in recently, it was showing a lot of 'garbage' characterss on screen - mostly '?' or '@'.  Having read around the forums and other pages, I figured this was bad RAM so have been replacing chips in and related to the RAM area since then. I've got myself a working set of 8 x 4116 chips and have put those in row C, all expansion cards have been removed. 

 

This is what it is doing now: The keyboard light comes on, and the screen fills with 10 vertical white bars. There is no beep (but I know the speaker works because there has been a bit of static coming through it before). Nothing changes from here, and the reset button doesn't do anything, although it does bring down the voltage on pin 40 of the 6502 down *a few millivolts*

 

The PSU seems to deliver the correct voltages, but I also have tried a brand new PSU which produced the same results. I'll explain what chips I've replaced in the next post.

 

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These are the chips I have

These are the chips I have replaced so far:

 

All of the RAM chips. There are two rows populated in the picture above, but I've mostly been testing with just row C populated.

LS257 at B6, B7 and C12

LS86 and B2

LS283 at E14

LS04 at C11

LS08 at B11 and H1

LS194 at B4 and B9

LS174 at B5 and B8

8T97 at H3-H5

8T28 at H10-H11

 

Of those, I think changing the address/data line chips (8T97/8T28) made the most different. Those were getting pretty hot in use. Another chip that gets pretty hot is the LS195 at C2, but I haven't replaced this yet. If it's missing, there is no display.

 

So I'm a bit stuck now - I'm not sure where to go next with this. I've checked the board and all the traces look ok, and I can use a multimeter to check voltages and continuity, but I don't have a oscilloscope and wouldn't know what to do with one if I had! 

 

Any pointers on what to check next? Thanks!

 

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