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581, 585 Power Supply Mod
If you own a Tektronix Model 581A or 585A Oscilloscope, you will want to check out this important modification for the high voltage power supply.
Purpose of Modification:
To reduce the failure rate of Vertical Output tubes (V1274 and V1284), internal arcing of the +350V series regulator tube (V737B), and to prevent contacts K601-4 from sticking.
This modification applies to the following instruments and serial numbers:
Instrument Serial Numbers
581A 3875 - 5069
585A 5969 - 9249
RM585A 100 - 1019

Step by Step Description:
  1. Locate the gray-red-brown wire on terminal 2 of K601. (See Figure 1.)
  2. Locate the two gray-red-brown wires in slot 11 of ceramic strip CSJ on the Sweep chassis (See Figure 2.) One of these two wires is the other end of the wire mentioned in step 1.
    Unsolder and remove these two wires from the ceramic strip. Using an ohm-meter, determine which one of these wires is connected to K601-2. Completely remove this wire from the instrument. If you do not want to damage the cable lacing, clip each end of the wire as closely as possible to the point where it enters the cable bundle.
    Solder the remaining gray-red-brown wire back into slot 11 of CSJ.
  3. Locate ceramic strip CSA on the rectifier bracket (see Figure 3.) Remove the bare wire that connects CSA slot 8 to CSA slot 12.
  4. Locate the two gray-red-brown wires in slot 9 of CSA. Unsolder and remove these two wires, then use an ohm-meter to determine which one goes to K601-1. Solder this wire into slot 8 of CSA, then resolder the remaining gray-red-brown wire back into slot 9 of CSA, where it was originally connected.
  5. Install a new piece of gray-red-brown wire from ceramic strip CSA, slot 12 to terminal 2 of K601.
  6. Locate ceramic strip CSD on the power supply chassis (see Figure 4.) Solder a bare wire from slot 7 to slot 8.
  7. Check K601 for welded contacts. Separate the contacts as necessary and burnish them to restore their correct operation.
  8. Update the power supply schematics in your instrument manual to reflect the modifications. (see Figure 5.)
  9. Visually inspect the instrument, then apply power and check for proper operation.

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Last modified on  2/29/00 10:07:54 PM