> On 26 Nov 2017, at 06:15, Tony Duell <ard.p850...@gmail.com> wrote: > > On Sat, Nov 25, 2017 at 11:02 PM, Adrian Graham via cctalk > <cctalk@classiccmp.org> wrote: >> Evening! >> >>> OK... Firstly, measure the voltage on pin 8 of the monitor PCB. Can you get >>> it to swing from 0 to around 12V? >> >> Yes, it tops out at 11.82V. > > Can you get it down to 0V?
Yep, it runs from 0-11.82V. >> >>> Scope the video output from the CPU board (on pin 2 of the monitor PCB). Is >>> it a good TTL level >>> signal? >> >> Yes. Given that it’s TTL and a 3-wire connection (composite plus H&V sync) I > > You mean 'video', not 'composite'. Composite is an analogue signal with the > video information and the syncs all combined Indeed. My brain was saying ‘video’ but my fingers typed ‘composite’ :) >> should be able to feed that into a PET monitor shouldn’t I? Wish I hadn’t >> given >> away my ‘big’ TRS80 Model 4 :/ > > I have no idea if the sync polarities are right, but you can try it with a Pet > monitor. A TRS80 Model 3 has the same monitor as the Model 4 of course. I’ll make up an extension cable I think, got more PETs than I know what to do with. I used to have multiple Model 3s AND a Model 2 but they had to go when I moved to a smaller house back in 2010. > (And I wish I could find a 4P over here….) Perhaps embarrassingly I can’t remember where mine came from but given I’ve had it since the early noughties that’s not surprising. It may even have been from a car boot sale. > > What happens if C101 is removed? Also try running it with TR101 > removed (or at least the emitter lead of that transistor disconnected). Nothing happens, in that the picture is the same as it is with both those components fitted. Cheers A