Thanks for that tip. And oh like some GM repair manuals where replacing an entire transmission might be 11 steps, but one of them is to use the $12,000 machine no one outside of the factory has ever even seen.
On Dec 8, 2017 1:38 PM, "Fugu ME100" <[email protected]> wrote: > It might be better to use the CLK (37) output as a reference if it is > needed. The CLK is derived from the X1,X2 XTAL inputs and should not be > impacted by the loading of the scope probes. > > The M100 reference manual is quite good for troubleshooting some parts, > although it does have a few broad instructions like “Check All IC’s”. > :-) > > From: M100 <[email protected]> on behalf of Brian White < > [email protected]> > Reply-To: <[email protected]> > Date: Friday, December 8, 2017 at 9:55 AM > To: <[email protected]> > Subject: Re: [M100] Fwd: Re: diagnose > > I noticed something a couple days ago. Those noisy gnd and 5v lines were > only like that because I happened to have probes on both X1 and X2 at the > same time. > > Later I was looking at a good M100, and happened to only be watching X1 > and others but not X2, and everything was much better. But just by touching > a probe to X2 while another was on X1, both gnd and 5v went exactly like > those pics I posted from the bad M100. I can probe either X1 or X2 and it's > fine, but not bith at the same time. > > I don't actually see any special reason to monitor either of those signals > except briefly to verify they exist, or to provide something steady to > trigger on while probing others. Just pointing out something I saw that > explains those ugly traces. > > On Dec 7, 2017 11:45 AM, "Josh Malone" <[email protected]> wrote: > >> Yeah - there is something very weird with the ground on that Tandy. >> Maybe some problematic traces? Or a bad IC leaking current to ground? >> >> Can you measure the DC power consumption? It should be ~60-70mA IIRC. >> >> On Wed, Dec 6, 2017 at 10:14 PM, Brian White <[email protected]> wrote: >> > After watching a youtube video about how to use an oscilloscope by >> sparkfun, >> > I switched all probes and channels to 10x and adjusted the trim caps in >> the >> > probes against the built in test signal to make the square wave look >> square. >> > >> > With gnd ref on the cpu gnd pin 20 instead of chassis gnd, and a couple >> > probes on X1 and reset_in, and one probe on chassis ground, now the x1 >> and >> > reset_in signals are steady, reset_in looks flatter, and only the trace >> for >> > chassis ground floats and bobs up and down now. >> > >> > So chassis ground simply floats around in relation to the rest of the >> board, >> > or at least in relation to the cpu. Not a bad afe in the scope. >> *chagrin* >> > >> > >> > -- >> > bkw >> > >> > On Dec 6, 2017 7:38 PM, "Brian White" <[email protected]> wrote: >> >> >> >> This is the bobbing I was talking about. It's dumb for me to even be >> >> talking about it yet since I haven't even done a basic comparison >> check on >> >> some other reference yet. >> >> >> >> https://youtu.be/b9jAYsfTOzQ >> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2Fb9jAYsfTOzQ&data=02%7C01%7C%7C33b7c3a9b7cd4909b28f08d53e64ed91%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636483525556528212&sdata=UvTz5UI2LRigb2jv0YVX%2BQqcwLR1LS1JpfYvVsiA3Ts%3D&reserved=0> >> >> >> >> And here's another look at a different signal hooked up a different >> way. >> >> Here, I have the ground ref hooked to the gnd pin 20 on the 8085, NOT >> the >> >> chassis ground. And CH4 is on pin 18, AD6. The offsets, trigger, and >> >> vertical scales are all visible on-screen. >> >> >> >> https://photos.app.goo.gl/mel4CKym2EtcV1352 >> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fphotos.app.goo.gl%2Fmel4CKym2EtcV1352&data=02%7C01%7C%7C33b7c3a9b7cd4909b28f08d53e64ed91%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636483525556528212&sdata=Z%2FNVGP3BjFaZW64aT0rMQteNAfXinZKhIC0XL6c%2BK%2Bk%3D&reserved=0> >> >> >> >> https://photos.app.goo.gl/K1AIj3Pmt15xXfR72 >> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fphotos.app.goo.gl%2FK1AIj3Pmt15xXfR72&data=02%7C01%7C%7C33b7c3a9b7cd4909b28f08d53e64ed91%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636483525556528212&sdata=vX%2FNje%2BZK0f1cDmSAeohlNWJlD%2BZi1%2FHbUawQmBi0y8%3D&reserved=0> >> >> >> >> >> >> -- >> >> bkw >> >> >> > >> >
