Thanks for the reply Chris, at some point, past when I'm comfortable that my unit doesn't have any functional faults that would require warranty claims, I will get inside, as I too was thinking it would be FPGA input thresholds, although again, as the FPGA history is vague on later units and knowing most of the devices used have separate supplies for banks of I/O, internals and perhaps a few other internal blocks, which could actually be lower again than the 3.3v main supply, the actual trigger point could be relatively low anyway. I note Camomille's circuit shows a number of lower voltage supplies, that could come into play. Once I get past that checking period, I will endeavor to see what the actual level is at the FPGA input. A nice thought about an internal pull-up possibly being enabled, as it would indeed influence the reaction to the external signals.
The only real item I had hoped somebody else could check, is if their units accept negative edge EXT triggers (on this round of software), purely from the functional aspect. Is mine typical or the odd man out? Please don't see that as anything pressing, it isn't, I can happily live with what I have found but if the unit has a fault, I'm in the window to get it replaced. Owon may even get back to me!
I have now resolved the Gould/Advance OS4000 DSO issue. It was one of the 1bit, 1K memory chips, from Intel (2102 static RAM). The data sequence coming out, isn't the same as that going in. I cannot source any of these, so have moved it to the lsb position, where it is hardly distinguishable. It had been a bit of a gut feeling for some time and I've contemplated putting a block of more modern memory in, even though most of it won't get addressed. I noted these old chips have very variable levels between them too, some marginal on TTL transition levels. I have some around 2.7v. The "stuck" bits make an attempt but never reach the threshold. The VDS1022i is pretty much superior in every respect to the OS4000, except nostalgia and my own appreciation of how it helped me produce, what were pretty unique designs at the time!
Good to hear you are also into audio! I have an omni-transmission speaker project running, that will eventually have 5 drivers per stereo channel, each driven separately to maintain damping levels. The lower end is taking some time to design, as it is inverse tapered transmission line loaded and using concentric tubes to reduce panel radiation. Top end is the Dayton air motion transformer, mid range is covered by two 3" metal coned units and the bottom end is a composite coned unit. The extended bass, when required, is likely a 10 or 12" but has yet to be bought. All but the very top end are forced to radiate in an omni pattern but forcing the tweeter becomes a bit pointless (and rather difficult, with the short wavelengths involved, so easy to produce lobes), although it sits in a spherical housing to minimize diffraction effects. Except the extended bass, which would be guilding the lilly, they are point sources. There are reflectors involved but well within a wavelength at their crossover points. Sorry, not intending to hijack the subject of these discussions!
Best regards!
EDIT: I had an acknowledgement from the UK Owon office, that my observations were sent to the development engineers and will respond when a reply is received. Owon certainly have a professional approach to customer liaison that should be commended, responding the 1st working day after I sent my observations. I'm certainly impressed.