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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

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

now. I should have checked the external sync too.

Thanks for your good help.

Jerry

Greg_A <<mailto:greg.a%40dslextreme.com>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

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

two. One is stable and locked, the other is very, very, close but not

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

would love to see a datasheet for U200. It is a Tektronix made IC, pn
0155-0055-00.

Jerry