If these components are OK remove jumper U on A13, cut pin 3 free and re-install the U jumper with only 4 pins on it. If it still does not work check C1601, C1602, CR1601 or C1603. With power off remove the brown wire shown on the lower left corner of schematic 13, be careful as there is -3KV on that wire, reapply power. Possible problems are shorted HV caps in the A11 PCB. Do not leave the power applied any longer than necessary as a critical bias voltage might be missing.ĥ) If it still does not power up put a voltmeter on U1910 pin 13, if more than 0.5V is present when power is momentarily applied then something is drawing excessive current. U2072 if the -5 is low and, U2086 if the -9 is low. If the +9 rail is low replace U2052 U2062 if the +5 is low. If the +50 V rail does not come up replace U2042 and repeat 4. Put a Voltmeter on the +50 rail and momentarily apply power. With the power off jumper TP1951 at pin 2 of U1910 to ground. This summing junction should be 0V for power to come up. If it does not then repeat part 2 again as another short has developed due to the shock of power being applied.Ĥ) At this point you have determined that power should be on but it isn't. Use similar logic to locate any defective caps on other boards.ģ) Now apply power and is all is well the power should come on. Go to the defective PCB, replace the defective cap and repeat part 2. pull jumpers E, F and K to isolate the A12 timing board and jumpers C, D and AA to isolate the A11 horizontal PCB. If the short disappears when the N and P jumpers are pulled then leave N and P out, move your ohmmeter to the defective rail on the A10 PCB and pull jumper L to isolate the A8 PCB. If no further shorts are found proceed to 3.
Once the first short is fixed re-install all the removed jumper blocks and repeat part 2 again.
Don't overlook R1579, which may be on the back side of A13 if the +5.5V rail measures low or open.
V&r vspd 485 series#
When you find the shorted one check the schematic to see if any series component might be damaged. Remove the associated capacitors while monitoring the DC resistance. Find the number of the defective cap from the TANT_PCB.XXX file that I downloaded to the forum. Before replacing the shorted cap you want to know if the short has taken any other components out. If the short still persists then the problem is on the A13, the power PCB. If the short persists then remove connectors on P1500, P1580, P1590, P1560 and P1570. If the short persists then remove the X, Y and Z jumpers. If you find one with low or 0 Ohms resistance start removing inter-board jumpers while watching the ohm meter. Look for empty sockets or burned or charred components.Ģ) Before applying power measure the DC resistance, to ground, of each of the 13 low voltage power supplies in your 485. Follow these steps in sequence for best results if your 485 ceases to run properly.ġ) Remove case and inspect all PCB's very carefully. I want to pass on a few troubleshooting tips I have developed as an aid to keeping your 485 running perfectly.