Real problem with mega st4

[galine]

Hello everybody,

 

Recently i found a atari mega 4 but it doesnt work it power on the key board led is green the screen turn on but i have a strange screen at the same of the tos screen

 

The floppy drive turn on ready but no acces ( when I put the machine on I hear a small mechanical sound)

I try tu unplug the first tos eprom and I turn on the machine and I have the same screen for have nothing i must unplug all eprom.

 

http://www.hiboox.fr/go/images/informatiqu...4bfb5f.jpg.html

 

 

I think is the tos who is out of order but I haven't eprom programator for try to reburn them and try again

 

I don't know what is the probleme and I hop I can have somes help here.

 

Thank you in advance Galine.

Edited February 20, 2009 by galine

[galine]

I have some news for my mega i put here all news possibility

 

 

 

 

1} check you have plugged the monitor plug in the right way up as most can be plugged in upside down

 

 

 

I haven't monitor or original scart ' make a homebrew d9 with RVB, sync, and ground I have already made that on another atari st and the cable works correctely.

 

2} you may find that the reset circuit for the machine has failed somehow

ive seen faulty/jamed reset buttons cause this issue

 

 

 

I think about that but i haven't idea were it can be wrong and i think if it realy that i will have just whit screen like when we push on rest switch no?

 

3} disconnect the floppy drive and any internal hard disks and try again

 

 

 

all my test are make with floppy drive unplug atari can start without.

 

4} the main mpu 68000 has failed

5} memory issues

6} the 32mhz dot clock has failed

 

 

 

I think the probleme is here but it's realy dificult to know were -_-. but I hope no cause i doesn't imagine make a spagetits plazza on my memory area (remplace all memory chip by one old pc memory) i havent the precision for make a good job and i take a risk to kill my dear mega 4 ^^.

 

7} the mono/colour monitor change over chip has failed 74F257??

 

 

 

I dont understand realy what you whant to say me what is 74F257?

 

Thank you for your help and sorry for my bad english.

[galine]

hello I haven't yet found chip for test my mega st but I kepp hope let me know if you have somes chip to sell me for try to see what is wrong thank you in advance galine.

[techie_alison]

Hi Galine,

 

Where are you geographically for starters? Francais? Come over to; http://www.atari-forum.com/search.php?sear...d=active_topics

 

More often than not it's something dead simple, so not a huge worry there.

 

Looking at your screen, it's the RAM. It's ALWAYS the RAM. Well, alot of the time it's the RAM.

 

How good are you at soldering? Ideally you need to get all of the chips out and get sockets in, so you can work by elimination.

 

Faulty TOS will just give you a blank screen and maybe some bombs. How many TOS chips are in there, 2 or 6? It is very unlikely to be the EPROMs.

 

RAM!

Edited March 19, 2009 by techie_alison

[galine]

Hi techie_alison

 

 

yes I'm living in france ^^.

 

Sorry for this long long time with no answer i work on other machines but my mega is always patient -_-. and if it's the ram i haven'n yet capacity for fix it -_-. I'm electronic learner. If you know someone who can remplace my old ram by an pc at ram I'm verry interested maby a dai i will cappable to make that alone^^.

 

I unplug plug all mobile chip and clean them all but no result.

 

 

for my tos it's a rainbow tos

 

Thanks for all Galine.

[galine]

I looking for tuto or topic about fix atari mega 4 ram or for a remplacement by a sim ram can you help me cause I haven't found that -_-.

 

thank you in advance Galine.

[techie_alison]

You have mail. :-)

 

...containing a 70-page PDF of the Field Service Manual that I've just spent a week writing.

[+poobah]

You have mail. :-)

 

...containing a 70-page PDF of the Field Service Manual that I've just spent a week writing.

Oooooooh!

[+poobah]

You have mail. :-)

 

...containing a 70-page PDF of the Field Service Manual that I've just spent a week writing.

Oooooooh!

[techie_alison]

Oooooooh!

 

Dahhhhhhhhhhhhhhhhh.

[galine]

hi,

 

Sorry for this long time without news it's not cause I win or totaly destroy my mega st just really overbooked with sommes other problemes. but now I have more time for my 2 mega st dead.

 

Yes I have realy say 2 a friend guive me a mega st 1 moded in 4 but with my chance it's also dead (20 bombs at boot screen nothing else)

 

I will send mod pics cause it realy beautifull I think i'ts an old mod cause it use an big card with on it the same ram chip like on the official mega 4 mother board.

 

I don't know if I must by me another atari cause with my legendary chance I will recive another out of order machine -_-.