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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Check this

Greetings and welcome the the Apple II coùmunity :-)

 

Looking at the pictures, is seems there is a mix and match of ROMs : D8 is the Applesoft BASIC ROM but E0 to F8 are Integer BASIC ROMs. Normally E0 socket should be empty but I don't think this is the cause of your problem. You can also remove the D0 ROM which is the Programmer's Aid as it's not required for normal operation.

 

The display seems to be working fine. No beep indicates the CPU is not working or not able to fetch instructions from the ROMs. So you can try :

  • testing the 6502 in another computer
  • replace C14 (74LS32), B11 (74LS08) and F12 (74LS138)
  • testing the ROMs into another Apple II

 

Good luck !

 

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Remove all the RAM except the

Remove all the RAM except the first 16K

Remove all the ROM except for the F8 Monitor ROM.

See if it boots to a * prompt, indicating that you are in the Machine Language Monitor.

 

I'd also suspect the 8T98 chips and its neighbours in Row H, which are address chips for the RAM and ROM.

 

Your system clock is working because you have video.  Could also be the CPU itself...

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Thanks Baldrick :) I have

Thanks Baldrick :)

 

I have previously removed all but row C, and have subsequently removed all ROMs except F8. No change unfortunately.

I've also replaced the 8t98s and close neighbours. In fact most of row H.

I have also swapped out the CPU for a known working one from a C64 disk drive (1541) which also uses a 6502. No dice :(

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amauget wrote:Greetings and
amauget wrote:

Greetings and welcome the the Apple II coùmunity :-)

 

Looking at the pictures, is seems there is a mix and match of ROMs : D8 is the Applesoft BASIC ROM but E0 to F8 are Integer BASIC ROMs. Normally E0 socket should be empty but I don't think this is the cause of your problem. You can also remove the D0 ROM which is the Programmer's Aid as it's not required for normal operati

Hi Amauget,

 

Thanks for the extra info on the ROMs! I've tried with just the F8 autostart ROM installed, and I've also tried another F8 ROM from a ROM card. Subsequently I've verified that the replaced F8 does work correctly.

I've now obtained a later revision motherboard that does work, so I'll be doing some swaps between them to try and localise the fault. Cheers for the help so far!

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