Easily replace ste mega ste and TT030 dma buffer ic's.

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Easily replace ste mega ste and TT030 dma buffer ic's.

Postby simbo » Sat Jan 23, 2010 12:11 am

Lots of people debate this dma issue,
however this is'nt the place to bleet on about the in's and out's.

If you want to change them or you cant get hold of a dma chip,
that allegedly is one with a repaired fault.
I've had this flaw using my atonce machine appear twice,
both times it wiped some data but I was able to recover easily.

You can see more info about dma chips in the hardware discussions pages;
Attached is a picture set that shows how to remove them and replace both ic's,
did think of a funky utube film but I just cant be bothered making it and i've things to do.

You need only remove the top cover and back of the floppy cover and drop out the floppy drive first.

Now you need a few tools.

a pair of radio plyers,
a sharp pair of sidecutters,
a soldering iron and some 22swg lead/tin/flux core solder
a 74HCT245 and a 74HC244 is fine
I used these however other ic's are possibly better,
in this one I just changed the two buffers as its dma chip is a good one maybe???,
this one also has an atonce emultion board and runs windows 3.1, and has tos 2.06.

In my other ste I used 74ACT type buffer, and also replaced a few other ic's while I was there,
that one has a faulty dma chip number, but runs perfect with multiple drives and usatandisk and has mutlitos X4.

ic's like
74ACT245 u302
74ACT244 u307
74ACT74 u308 I used a F type here again no act avalible

most important is U305,
I use a 74F06 here as I couldnt find 74ACT06,
this helps poor floppy tie up and data loss {packet loss} with modern 1.44mb drives interface's,
and also a hdd signal is buffered by this ic and this is the worst offender.

Anyway; at the top of each pic is some advice tips etc..
remember to place the ic's in the fresh cleaned pin holes the right way around,
with pin 1 going the right way or your gona damage things.

once fitted check for any shorts or shards of metal around the pcb and any pulled pins you didnt discard etc.
you should be carefull not to drop any in the first place...!!!
you now can test your work.

If you test an atari ste anyway... for one, with the floppy disconnected youll get 4 bombs,
just before it gets to the desktop; basicaly when it tries to check the floppy drive.
add back the floppy, setup the hdd or usd and test the atari accesses the drive's both hdd and floppy.
Any errors shut down at once and check your work.
reassemble and test it all works fine.
your ready to rock!

changing the buffers is upto you and will cure many issues with packet loss
read the details about this dma issue in other post before deciding,
but finding a dma chip maybe harder and a bit harder to change a soldered on one
the same method however applies.

Few things;

Try never to use sockets when using TTL or any other ic's that carry signals at speed
the added capacitance a socket introduces and can cause issue's and the same applies to the dma chip or floppy controller.
A socket is a BAD idea electricaly anything clocked over 5mhz should'nt have a socket on it is a basic rule.
I very seldom use them even turned pin types are just as bad.

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