phs172m@vaxc.cc.monash.edu.au (Stephen Harker) (12/07/90)
I had a dead 10MB ProFile drive, and did not want to spend the money asked for a external SCSI drive here in Australia. When I had asked earlier in the year about formatting a ProFile one response mentioned using the ProFile case and power supply for a MiniScribe drive. With this in mind I decided to convert my ProFile to a SCSI drive. This article describes the work I did, I hope it is of interest. Materials Required SCSI drive (surprise), 2 Centronics 50 pin connectors (crimp on type), 1 50 pin female PC connector (crimp on type), 1 12V fan of approximately 6cm radius, 1 hard disk power connector (4 pin female), 1 two pin power connector for fan. Approximately 20cm of 50 wire ribbon cable (I bought 0.5m). Access to some metal working equipment - hacksaw, metal drill bits and preferably a spot welder. Sheet steel of similar gauge to the backplane of the ProFile. Removing ProFile innards The ProFile case is opened by undoing three phillips type screws located under the front lip, and four phillips screws holding the two back metal plates in place. Once these are removed the top can be removed by pulling the front lip forward slightly and then lifting the top half off. Inside the ProFile (looking from the front) is the power supply on the left with a logic board on top of it, the drive is on the right with with an Apple logic board under it - attached to its frame. The logic board on the left is easily removed. To remove the drive and its frame you must undo four phillips screws under the ProFile case, a ribbon cable linking the two Apple logic boards, the two power supply connectors and an earthing strap. These could be removed carefully and put into an antistatic bag if you know anyone who could use them. Power Supply The power supply on my ProFile was rated at 65W according to Apple's sticker on the back of the ProFile. However while their data sheet on the ProFile said 35W. However either figure should be enough for most drives, the one I bought was an internal Quantum 40S rated at 8W. I bought it from Injan Pty. Ltd. (a Mac supplier) in Sydney for $Aust699, plus $Aust10 shipping. There is enough room and power to run two such drives. The power supply has two set of cables, one has 12V and earth - this is good for a 12V fan. The second has +12V, +5V, -12V, Earth and a AC check for the logic boards. For a standard hard disk connector you only need +12V, two Earths and +5V. The color codes for the wires derived from the connector list on the power supply case (240V) are:- red +5V 2A blue +12V 1.5A white AC O.K. purple -12V 0.15A black common (earth) You need to buy the standard hard disk power connector, (most electronic stores should have them). The wires going into the drive, looking from the back are from left to right: +5V Earth Earth +12V Check this carefully with a reference, before connecting to a drive. Metal Work (i) Backplane The next step involves metal work on the backplane to support a fan and the standard SCSI connectors - Centronics C50's. I spot-welded a strip of metal to the backplane to give a location point, this strip was 2cm wide and 5.5cm long, it looks like this (again viewed from the rear): O N OOO O O N OOO O O N RRROOOOOOOOOOOOOOOOO O N RRRROOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Strip viewed from side (actually two strips spot welded): NNNNNNNNNNNNN NNNNNNNNN Where O represents the old metal, and N the new metal, and R metal that had to be removed. The Centronics connectors went on the left, and the fan in the area that the metal was removed from. I did not try to cut out the metal to give a circular shape for the fan. You will need to file off the coating of the backplane in the position for the added strip. (ii) Drive support To support the drive two L section brackets were made from sheet steel to support the drive, looking like this from the front: L L LDDDDDDDL LDDDDDDDL LDDDDDDDL L L LLLLLLLLL LLLLLLLLL Where D is the drive and L the sheet steel. You need to drill holes in the brackets to fit the old ProFile bracket location holes, and holes in the side to fit the drive. I found the old bolts that held the ProFile drive and bracket together to be useful to bolt the drive and brackets together. Connections From an article (cross-)posted in August this year by Thad Floryan, the SCSI connectors and drive are supposed to be connected in a daisy chain like this: ______________________________ / \ [] | \_ Drive / [] | \______________________________/ With the [] being the 50-pin Centronics connector. I found it easiest to wire up the connectors - the wires are straight through so with crimp on connectors there should be no problem (except the crimping - I ended up hitting one connector with a hammer!!!). I used only 8cm of ribbon cable between the 50 pin centronics and the Drive, ie about 16cm in all. According to SCSI specs the cable should be no more than 10cm (Thad Floryan again). Again I found it easiest to fix the fan into the backplane, fix the drive in the case (making sure that all the earthing connectors are in place), before attempting to connect the SCSI connectors. I connected the 50pin PC plug to the drive first then screwed the Centronics plugs to the backplane, taking earthing precautions (drive plugged in etc.). I also connected the ProFile "Ready" LED wire to the drive access indicator (this was a molex type connector, possibly since I had told the supplier that I intended putting the drive in an case). Results My drive works well, it is much quieter than the old ProFile, as well as much faster. It is also far quieter than my GS with its genuine Apple fan in it! I am using the Apple DMA SCSI card and with a 1.2MB system it boots in about 20seconds, and loads all modules of AppleWorks GS in about 20 seconds. It is amusing that it still looks like a ProFile from the front, but has so much higher performance. The only obvious difference is the behaviour of the "Ready" light - it is now disk activity. The back finishing plate still needs some work so that the drive looks better, but this is best left to the end, so that you get the modifications to the holes correct. In my case I did some work earlier which turned out to be wrong, so the plate will not look as good as it might. The main disadvantages are that to change the SCSI ID you need to open the case. Also the drive uses internal termination which requires the case to be opened to remove it if you want to chain from the drive. However it is a genuine daisy chainable SCSI drive and the fan ensures that it keep cool, I did not want to rely on convection as the ProFile does. All standard disclaimers apply, don't try this if you don't have some confidence in your ability to get the wiring correct. In particular I don't know what differences there are in the 110V supply, however the wiring should be the same. On the other hand I found it to be a reasonable project, and having access to some metal working facilities here at Monash University made things easier - or possible in the case of the spot welding. -- Stephen Harker phs172m@vaxc.cc.monash.edu.au Monash University