Strange failure on apple IIe motherboard

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Strange failure on apple IIe motherboard

Hi

I have 2 Apple IIe motherboard and a power supply

when I power the first board, the screen is cleaned and then the simple word "Ram:" is written on the top left corner...
nothing else. I deduced (I may be wrong) that the board is working but lack peripherals and specially a keyboard
(if I remove the 74LS154 decoding the IO I get "Apple II and a prompt"

on the second board, the screen is filled with little colored squares (I guess it's just low resolution) an nothing else.
if I put the rom of the previous board to this one, I columns on screen patterns containing '*'

apparently on of the set of eprom is enhanced the other set standard

any idea to what I should look to solve the problem of the board with the screen filled with colored squares ?

I try to swap many parts without real success...

any idea ?

thanks

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Re: Strange failure on apple IIe motherboard

I Recall reading somewhere that on the Apple ][e, if there is no keyboard, the computer goes into a test mode, with the Blinking Squares..

Can you use the Keyboard to start the Self Test ( Ctrl-Closed_Apple-Reset )

MarkO

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Re: Strange failure on apple IIe motherboard

I dont have any keyboard right know, I'm waiting for a adapter to plug an usb keyboard...

I'm not to worried about the first board, I guess it has a good chance to work with a keyboard and a disk.

but for the board with the screen filled with small colored squares I'm more worried
something is obvious broken

I checked a pdf of hardware failure on Apple IIe but I've not seen this case described

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Re: Strange failure on apple IIe motherboard

by swapping parts, I get strange results

Apparently I detected 2 bad rams chip, I replaced them

on the board with standard rom/6502 I get a black then white screen then a kind of reset and it starts again
if I remove the 74LS154 I get "Apple ][ on the screen and a prompt"

on the board with enhanced rom/6502 I get 2 alternating screens composed of small squares...

at some time on the one with enhanced rom/6502 I got a patten RAM 0 0 0 1 0 0 0 0
the pattern was changing when I swapped the ram chips since I replace the chips I dont get the pattern anymore

on the standard rom mother board, it just displayed "Rams" on top of the screen

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Re: Strange failure on apple IIe motherboard

I didn't read everything carefully, but I did see you didn't have a keyboard. An Apple IIe will not boot without a keyboard (or test fixture) plugged in. If you don't have a keyboard, it will cycle through the self-test (colored squares for ever). Some type of burn in process I presume.

Jay

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Re: Strange failure on apple IIe motherboard

thanks

it's good news, it probably means that after having fixed the broken ram, both board are just probably working
and waiting for a keyboard

thanks to all

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Re: Strange failure on apple IIe motherboard

Hello,


on the board with standard rom/6502 I get a black then white screen then a kind of reset and it starts again

on the board with enhanced rom/6502 I get 2 alternating screens composed of small squares...


You describe the diagnostic screens with unenhanced and enhanced ROMs.
This is the normal behaviour since no keyboard is plugged in.


at some time on the one with enhanced rom/6502 I got a patten RAM 0 0 0 1 0 0 0 0
on the standard rom mother board, it just displayed "Rams" on top of the screen

If this appears, you probably have defective RAM chips. 1 show the positions of bad RAM chips according to the motherboard layout.

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Re: Strange failure on apple IIe motherboard

with a keyboard, both motherboard works

1/ still had some memory problem fixed by changing the bad ram chips.
the screen is very clean, the characters are really nice. (even in 80 col)

2/ the second board works but in 40 Col the characters are slightly blurred..
in 80 col it's almost totally usuable.

any idea for this blurred characters ?

thanks for your help

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Re: Strange failure on apple IIe motherboard

Hello,

any idea for this blurred characters ?

A picture would help but here is a starter if you're using a PAL motherboard and a B&W display. There is a switch located at B-C 15, on the right side (see enclosed picture).
With a monochrome display, you have to select the MONO position. Otherwise (in the COLOR position), the characters will be blurry.

IMAGE(http://img11.hostingpics.net/thumbs/mini_630809AppleIIeMotherboardFront.jpg)

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Re: Strange failure on apple IIe motherboard

I'm using 2 ntsc motherboards with an adapter + vga flat screen

video composite --> HDMI --> vga

works fine one a board
blurred on the other

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