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Hi Gang:
Whenever I have a 485, or any other scope for that matter, in my shop for refurbishing I always tap on every potentiometer with a screwdriver handle end while watching the CRT.? If I see any flickering I replace that pot.
As to the shortened trace I would strongly suspect the X6 voltage multiplier, U1600.? The failure pattern for U1600 is a short trace in the center of the CRT.? Sometimes the trace is not visible for several seconds after applying power? To determine if U1600 is putting out 21KV proceed as follows:
1) Disconnect all inputs to the neck of the CRT.? This opens a return path for a high voltage arc which will happen next if U1600 is good.2) Apply power and wait about a minute.3) Remove power and immediately pull out the high voltage connector at the left rear of the scope.? Move the removed end near the CRT metal shield and if you get a big spark you know U1600 is OK.? If you leave the 6 neck connections on the CRT when doing this test you will have an excellent chance of killing U660, the vertical amplifier output.? This fact was verified by me the herd way, I lost two U660's
If no spark occurs you know the X6 multiplier is bad and must be replaced.? They are available as a new item from Voltage Multiplier Inc., Visalia, CA as item VM176.? Price a year ago was $150 each.? If you replace U1600 carefully check R1602, a 15K, 1/2W resistor.? It is frequently toasted if U1600 is bad.
The 485, in my opinion, is the best analog scope Tektronx ever made.? It is versatile, robust, small, has excellent bandpass,? reliabile, fairly easy to repair and has many features that are outstanding.
Good luck but, whatever you do, do not trash it.
Reed Dickinsonreed714@...