On Dec 16, 2011, at 11:25 AM, Brooke Clarke wrote: > Just a guess. If line triggering does that there may be a problem with the > power transformer. > Use an Ohm meter to locate the transformer terminals for the AC line and then > check from one of those to all the other terminals. > I suspect there's a short in the transformer. > Look at U502 to see of it's burned up.
Thanks for the thoughts. U502 is interesting. It's a small PCB with an 8-pin SOIC and an SMD cap on one side soldered into with a two rows of 0.1" pins into the main PCB. Since it's only a 8-pin IC on top, and U502 is supposed to be a quad comparator, likely there's another 8-pin IC on the bottom on the adapter board. I'd need to desolder the 14-pins to check that. I suspect that SOIC to DIP board is there because the original U502, a MC12040, became unavailable. I'll need to do some more disassembly to check resistance between the primary and the secondary taps. I was wondering about the transformer or other power rails as well. That's why I checked the 6 regulated outputs. While the sonic noise with 'line' triggering is an important clue, I was thinking it was probably more in the logic circuitry since the other 4 trigger modes won't trigger. Unfortunately, I don't have a schematic. Anyway, thanks again for the information on trimming C512. Kevin _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.