Stepper Motors for the Sputtering System ------------------------------------------ Initial Rev. Apr-2025 Current Rev. 13-Sept-2026 April 2025 ---------- One of the stepper motors for the Rm B148 Sputtering System did not work when Bob tried to use the system. I believe that none of the LEDs on the "Zeta Drive" came on. I worked on the Zeta drive long enough to determine that: - The thermal fuse on the big internal power resistor was open. I believe that this resistor has something to do with one of the Damping systems in the drive. Jumping the thermal fuse did nothing. - It was clear that the drives internal power supply was not running, i.e. the supply for the Analog circuits and Digital logic inside the drive was dead. - Repair did not look fast for easy. With Norman's support Bob purchased a used drive. I believe that it came from some one in Minnesota. - The new used drive worked OK - the sputtering system was running again. The dead drive was put back together and a label was put on it explaining its history and its condition. - All was OK for some months then 12,13-Jan_2026 -------------- - Early Monday morning Reza and Demet have stepper trouble with the sputtering system. When I arrived they had put: the dead driver that had just failed today, the dead driver that failed in April 2025, and the one and only good driver (the used driver purchased in April 2025) all in B112 for me to look at. - I started by working on the driver that had just failed today. It look same as the one that failed in April 2025, i.e. none of its LEDs were ON and the thermal fuse on its big internal power resistor was open. - NOTE: These drivers use a HOT power line connected internal power supply. The line AC is full wave bridge rectified and fills the 2 large electrolytics (which are in parallel) to about 180 V DC or so. This HOT line connected 180 V power is the power that is used to run the motors. I believe that the motors are run via two full H Bridges. All of that circuity is HOT at line potential. - The bulk 180 V DC is also the power source for this drive's Internal Supplies. I believe that the internal supplies are: +5V that is used to run the 3 series Xilinx FPGA and the other internal logic, About +12V that is used to make +8V for the Analog circuits and -12V that is used to make -8V to run the Analog circuits. - The Internal Supply uses a XC3843 controller. This controller regulates on the +5V output and then uses 7808 and 7908 to make the regulated +-8 Volt rails from their +-12 Volt bulk supplies. - The Switch Transistor for the flyback supply, the diode for the +5V output rail, and the 7808 & 7908 are all spring clip mounted to a heatsink boss along with a large switching FET for the Damping system. There is no easy way to remove the spring clips so that you can remove the boss so that you can access the pcb and components that are under this boss. - The UC3843 was not running. The Vc/Vcc input power to it was still too low. The supply power to its VC/VCC power pins was still under the 8.4 Volt Lock Out point. The power feed to the Vc/Vcc pins is: 2x (2x 49.2k Ohm) = 40.2k Ohm to the Raw filter 180V input bus and once the UC3843 starts that a winding on the Flyback runs. There is a (I belive) 100 uFd 35V aluminum electrolytic to ground on the Vc/Vcc pins. I believe that it was leaking enough to pull down the startup supply that comes via the 40.2k Ohm composite resistor. I replaced this aluminum electrolytic. - The supply now runs but its +5V output is only 3.5V and the inputs to the +-8V regulators are also too low (by about the same factor) for them to work. This was all caused by open aluminum electrolytics that are right after the rectifier for the +5V supply. There are 3x 100 uFd and 1x 47 uFd at this point. I paralled one of these with a good 100 uFd capacitor. The +5V bus then came up to +5V and the +-8V supplies are also working. - All of this debug work had been done on the drive that just failed on Monday. The issue is how to put this supply back together because the spring clips are now bend and one of them is broken for the heatsink boss for the internal power supply. - Instead I made the same reairs to the Drive that failed in April 2025, put it back together, gave it to Reza and Demet, and so far I think that it is running OK. - Issues: Finish fixing and put back together the drive that just failed on Monday. The "repaired" drive that is now back in use had only one of its 100 uFd caps in the cap input filter for the +5V bus replaced. Clearly all of these cheep junk no lable SMD mount aluminum caps need to be replaced. The big Al Caps in this thing are only 85 deg C junk. Reza leaves these drives ON all of the time and clearly all of these caps have cooked themselves - just like the still open thermal fuse on the big Damping resistor. Reza said that he would start unplugging these drives when they are not in use. We also need to ground the metal case of these stuupid drives with their line hot internal power. - NOTE the blind vias in the pcb of this drive.