=*=*=¢ ATARI 1050 DISK DRIVE REPAIR¢ Defective Head Park Switches¢ By D. R. HAULSEE¢ Reprinted from M.A.G.I.C.'s¢ Newsletter by OL' HACKERS,¢ with thanks!¢¢ (I downloaded this article from one of¢ the bulletin boards that I visit. I¢ can't remember which one or when I¢ found it. I have absolutely no idea¢ if this mod works so you're on your¢ own. - Grant - 8 BIT Librarian of¢ MAGIC.) (Editor, DITTO! OHAUG AND I,¢ are not responsible if it doesn't¢ work! A.P.)¢ ¢ DESCRIPTION¢¢ One possible failure of an ATARI¢ 1050 disk drive that will cause¢ endless boot errors is a failure of¢ the sensor that detects if the read¢ head is parked. This sensor is¢ currently NOT reaadily AVAILABLE as a¢ replacement part, but MUST be in¢ working order for the drive to¢ operate. This article will help you¢ to replace it with more commonly¢ available parts.¢¢ TOOLS NEEDED¢¢ #2 Phillips head screwdriver¢ #1 Phillips Head screwdriver¢ 30 watt maximum soldering iron¢ Small flat blade screwdriver¢ Small needle nose pliers¢ Epoxy or equivalent glue¢ Xacto Knife¢¢ COVER REMOVAL¢¢ Turn the 1050 on its back and¢ remove the 6 phillips head screws. ¢ Carefully turn the drive back onto its¢ feet and set it down. Gently lift the¢ back of the cover and slide it¢ forward. The front bezel will come off¢ with it.¢¢ DIAGNOSIS¢¢ The head assembly slides on¢ tracks and is driven by a stepper¢ motor located to the right of the disk¢ platter. The head assembly has an arm¢ that sticks out to the left. This arm¢ slides into a u shaped sensor when the¢ head is retracted.¢ Connect power to the drive but do¢ not attach it to the computer. Turn¢ the drive on (do not put a disk in the¢ drive). As the drive powers up it¢ must find the location of the read¢ head. If the head is parked, it will¢ index the head forward until it clears¢ the sensor and then repark it. If the¢ head was not parked, it will retract¢ the head until it is parked.¢ If the sensor is bad, the head¢ will index forward 1/4 of inch and¢ stop. Every time the drive is turned¢ on the head will index forward. ¢ Eventually the head runs out of travel¢ and will bang repeatedly on the¢ forward stop. When connected to a¢ computer, you get a boot error because¢ the drive cannot find the boot¢ sectors.¢ As a final test, disconnect the¢ J10 connector on the circuit board. ¢ Do not pull on the wires!!!!! Use the¢ needle nose pliers. It is the next to¢ last connector on the back left of the¢ circuit board. When the connector is¢ removed, 4 pins will be exposed on the¢ circuit board. Jump the front two¢ pins on the board together and turn on¢ the drive. If everything else is¢ alright the head will begin to¢ retract. As soon as the head begins¢ moving, turn the drive off and remove¢ the jumper. If the head did not move¢ backwards then the problem is in the¢ circuit board or the stepper motor. ¢ That is beyond the scope of this¢ article.¢¢ DESCRIPTION OF THE SENSOR¢¢ The sensor is composed of an¢ infrared LED and an infrared photo¢ transistor. Either one of the pair¢ could be bad. I have not found direct¢ replacements for them, but, a pair¢ made by Radio Shack will work. The¢ LED is part number 276-143A and the¢ receptor is part number 276-145. ¢ Please note, these parts are larger¢ than the original parts and will not¢ fit into the existing sensor housing. ¢ You will have to fabricate a housing¢ for them.¢¢ PROCEDURE¢¢ 1. Remove the sensor from the drive. ¢ The wire tie to the frame must be¢ cut.¢¢ 2. Cut the sensor from the wires. ¢ Orient the plug as it goes in the¢ drive. Place shrink tubing over the¢ wires and then solder the parts to the¢ wires as follows. The order is from¢ front to back.¢¢ 1st wire-emitter of part 276-145¢¢ 2nd wire-collector of 276-145¢¢ 3rd wire-cathode of 276-143A¢¢ 4th wire-other lead of 276-143A¢¢ After soldering, position the¢ shrink tubing over exposed connections¢ and heat it.¢¢ 3. Plug the J10 connector back into¢ the circuit board.¢¢ 4. Fabricate a mounting that¢ positions the LED vertically looking¢ down. The mounting must have fore and¢ aft adjustment and position the LED¢ above the arm on the head unit. The¢ arm on the head unit must pass under¢ the LED. Ideally,the photo transistor¢ pair should face each other. ¢ Unfortunately, there is not enough¢ room under the arm for thr receptor. ¢ By trial and error I discovered that¢ the receptor can be placed on its¢ side. The LED though must shine¢ directly into the receptor.¢¢ 5. Fabricate a mounting that¢ positions the receptor horizontally¢ looking toward the head mechanism. ¢ The mounting must have fore and aft¢ adjustment and allow the arm on the¢ head unit to pass over it. I cut the¢ original housing into pieces and glued¢ the LED and receptor to halves of the¢ mounting. I then used standoffs to¢ set the parts to the correct height.¢¢ 6. Turn the drive on. As the drive¢ powers up it will position the head¢ over the sensor pair. If the head¢ will not position, check to make sure¢ that the wires are properly¢ connected.¢¢ 7. Now that the head is being parked,¢ make sure that it is parked in the¢ proper place. As a starting position¢ the back end of the head mechanism¢ should be 3/8 of an inch from the¢ inside boss that holds the arms that¢ the head slides on. If the location¢ is wrong, turn the drive off and move¢ the sensor pair as required. When the¢ drive is turned back on it will repark¢ the head. Continue moving the sensor¢ pair until you get the 3/8 dimension. ¢ The sensor pair is only moved with the¢ drive powered off.¢¢ 8. Connect the drive to the computer¢ and attempt to boot a disk. SPARTADOS¢ is less sensitive to head location¢ than DOS 2.5. If the disk boots, run¢ some programs to check that the drive¢ can read all disk sectors. If the¢ drive can not read all sectors or will¢ not boot then move the sensor pair a¢ little forward or backwards. My two¢ drives both held a dimension of 7/32¢ of inch on the gap referenced above.¢¢ 9. Be patient. Eventually you will¢ get the correct gap. Reassemble the¢ drive cover and you are finished.¢ =-=-=¢¢
