Greg,
Thanks for your good suggestion. The signal at the input of the trigger generator looked great and I assumed the balance circuits was okay. I checked the adjustment for trigger balance and found that the junction of r200/c200 was at -3V rather than +65mv. I adjusted for the +65mv and it syncs very good now. I should have checked the external sync too.
Thanks for your good help.
Jerry
Greg_A <greg.a@...> wrote:
Jerry hi,
I looked for you schematics and I think you could concentrate on signal flow from Q184, Q190 up until U200 pin #15 - that should be trigger in for that chip.
Greg
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At 07:13 AM 2/4/07 -0800, you wrote:
Greetings,
I have an SC501 that has poor sync. The unit works better at Usec settings than Millisec settings. I can swap U200 with a unit that works good and see no improvement. I can set 2 units side by side on extenders and compare voltages and waveforms and not see anything suspicously different between the two. One is stable and locked, the other is very, very, close but not stable. When the sync on the bad unit is at it's most stable point, the blanking output slows dramatically and the screen flickers.
The power supply voltages are good with no apparent ripple. The Msec timing cap, C230 measures the same on both units(0.987uf and 1.02uf).
I am attaching the schematic for the U200 circuit. Suggestions are welcome. I would love to see a datasheet for U200. It is a Tektronix made IC, pn 0155-0055-00.
Jerry
