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,

dvador wrote:

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.

dvador wrote:

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,

dvador wrote:
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.

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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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