3 1/2" DRIVES FOR TI

(Reprinted from TI DBITS by John Parken of TI-Chips)
The 5 1/4" format of the TI has been a plus because 5 1/4" disks have been more or less set aside for the more popular 3 1/2" format on the PC. The people who get rid of 5 1/4" disks because they don't use them anymore give me a good source of disks to reformat for my TI. People get rid of disk files full of double sided double density which work fine with the TI.
For people who are putting no more money into their TI, you can buy 3 1/2" drive for use with your TI till you decide to retire it. Then recycle them on your IBM system. If you have a Corcomp disk controller you can use 3 1/2" disk drives and only need low density disks for them. I have thought about putting 2 3 1/2" drives in my system because I have seen so many 3 1/2" disks on sale with a rebate for their whole purchase price. I just bought 100 Sony disks for $39.00 and got a $30.00 rebate check, 9 cents a disk. Hard to pass a deal like that up. I can't understand how the manufacturers can make any money off a deal like that but I love them.
I wrote this article in another article, then I bought two 3 1/2" drives and found things not to be as I thought. That prompted me to get it working before I submitted the article as true. So here we go.
When hooking up 2 3 1/2" drives on the Corcomp disk controller card in addition to the two 5 1/4" drives you have in the P Box, no problem right! Well drives have changed, all IBM 3 1/2" drives are set up for drive 2, which for IBM is OK. These cable takes care of selecting drive 1 or 2, but what about my TI? Gone are my drive select jumpers and no select as to high or low density. I can use the same approach as IBM uses. I will do my switching in the cable: pin 12 or wire 12 is the drive select #2. If I want drive 3 all I do is move wire #14 coming out of the disk controller to wire #12 into the drive. The disk controller will then consider that drive as drive #3. The drive select lines on a Corcomp card are 6=drive #4: 10=drive #2: 14=drive #3:
The drives I used I bought at a show for $19.50 each. They are Neutronics 3 1/2" 1.44 meg. At the show I also bought the splitter cable to power the drives. I did have to go to two different tables to get the right combination I needed. First a Y 5 1/4 (larger connector) to get my power outside of my P Box. I did experience some problems with the 3 1/2" drives by just using the P Box power supply so I did add an external 5 volt power supply. The supply I used supplies 1 amp 5vdc. You can buy a wall plug-in 5 volt power supply from Radio Shack, when you hook it up the black and red wire are GND and 5VDC.
Then a double 3 1/2" (small connector). These 3 1/2" drives only need 5VDC. Use a volt meter to see which wire from the wall 5 volt power supply are GND and 5VDC. A 24" length of 34 conductor ribbon cable with one 34 position card edge connector and 2 34 pin socket connectors make up the cable. All odd pins are at ground potential.
Please remember this is for a Corcomp disk controller only. Even when you use a 3 1/2" 1.44 meg drive it will only format your 3 1/2" disks to 360k and only if you cover the density hole with tape (black) or use some of those write protect tabs.
As I wrote this article I built the cable. Then I tried it. It did not work. The drive lights came on (all four) all the time. Upon further inspection when the card edge connector was crimped on it was off just enough side to side to short all the pins together. I cut off that connector and recrimped a new one and problems fixed. These connectors should be available at Radio Shack. Having the 3.5 drives is nice. Again TI is a winner only because we do have some compatibility with IBM equipment.
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