11.5.7 CENTurbo2 DMA modification

CENTurbo2 DMA modification

First thing when doing any soldering on your Atari, make sure you have the correct type of soldering Iron and solder. A 25 watt iron is fine and you can use a 30 watt if you are careful not to over heat the componets your working on. Anything over 30 watt will be too Hot and you risk heat damage. 60/40 solder is about right. Also, try to get a short soldering Iron, the long ones are hard to do detailed work with. And also use a pencil point soldering tip for detailed work. And make sure that the soldering Iron Tip is clean. Dirty Iron Tips will not solder correctly. And can cause heat damage. If you have a dirty tip, take a knife and scrape it clean, then heat the iron and put solder on it. Then let the iron cool, before using. While soldering use a Very wet sponge or cloth to clean the Iron tip clean as you solder. It's very important to keep the tip clean when soldering.

Now on to your problem. As far as I know there is only one PCB track in the area where the DMA modification is done. If you have the CT2B paper Manual there is a diagram on page 3 or 4 which shows the SDMA (U36), the PCB track, and the AJAX chip (U20). The PCB track starts out from the 2nd pin of U36. Start at the top left hand corner of U36 and count the pins down toward the keyboard and you'll find the 2nd PIN as we will call it. The PCB track starts at the 2nd PIN and runs straight across the board then makes a sharp turn up to go around 2 black inductors. I believe the first top inductor is labeled L66.

This PCB track has to be CUT into for the CT2B DMA modification and also for the 25/50mhz Nemesis Buffer modification.

Most folks cut the track right around where it corners those 2 inductors. So the only connection is to the 2nd pin of the DMA (U36).

First thing I would do is to solder one end of the 100 Ohm resistor onto pin 14 of the AJAX (U20) chip.

Then go ahead and solder the CT2B wire onto the other end of the 100 Ohm resistor.

Now for the connection on PIN 2 of the DMA (U36) chip. Make sure there is no stray solder on the PINS of the DMA chip. If there is, you must remove it some how. Either by some careful desoldering, or by taking a small sharp knife point and scraping it off.

Alot of times, stray solder doesn't completely setup if it lands on cold Pins and etc. So its easy to just pick off if this is the case. Just be careful if you have to remove stray solder.

Now you should be able to use a componet leg cut from a resistor or other componet for the replacement PCB track, Or a small wire. If the original PCB track is completely gone all the way up to the PIN 2, then you will probably need to take a small sharp knife and carefully scrap the Top of PIN 2 so that you can make a soldering connection.

You'll need a length of wire or componet leg long enough to reach from PIN 2 to the Resistor/CT2B wire connection that you made earlier.

After you have all this right, go ahead and carefully solder the wire or what ever you are using to PIN 2. I would use only a small amount of solder and put some on the wire or whatever you are going to use as a PCB track first. If you could get a small amount of solder on the wire/etc then you could just touch the wire/etc to PIN 2 and heat it with the soldering Iron. Just be careful not to use to much solder or you'll end up connecting the other PINS of U36 together. You'll see that they are small anyway and close together. A Pencil Tip for the soldering Iron is good for this connection.

If you can get this connection done right. Give it time to cool. Then all you have to do is simply connect the other end of the wire/etc to the Resistor/CT2B wire.

This should work if done correctly. AFAIK there are no other connections that will have to be made.

If you don't feel that you can do this, then any good electronic person should be able to do this easily. Maybe the person who installed the CT2B for you can do it.

phantomm@kih.net