Figuring out why an instrument doesn't trigger on something it should "see" is often a tricky problem. However, if they claim a 3 MHz bandwidth, there's probably something that they know about its internal workings that don't jump out at you when perusing the spec's. Perhaps, as was the case with many non-TEK 'scopes in the mid-late '70's, some simply couldn't do it. A really precise and very sensitive trigger circuit is quite costly, and until the early '80's TEK used a very costly circuit that outperformed everyone else. By 1980, or so, HP figured out how to trigger nearly as well with a less costly circuit, so, after a few years, that's what everyone, including TEK was using.

If it samples in the 100-MHz+ range, it should be capable of better than what you describe, but if firmware is involved to any extent, it may, as you've suggested, have "issues" with slow signals sampled together with fast ones.

BTW, I can still get a nice, crisp, display with my 475A, when, often enough, my 2467B's won't trigger reliably on the same signal without a lot of fiddling.

RE