Hi, I have a not working Olivetti M10 and a Rigol DS1104Z oscilloscope, so I made few measurement to try to help Brian and in the mean time try to troubleshoot my unit.
My unit was working properly and stopped as soon as I flipped the NiCd battery switch off while the unit was ON (done by mistake with the cover open). Now the screen turn on but I can regulate just the contrast and no text appear on the screen. I also made a small arduino circuit to test the LCD alone, and I'm able to write text on it, so the LCD should be fine. BTW I think Brian is using way too long ground leads on the oscilloscope probe. I made my measurement clipping the alligator clip to the metal case of the main crystal that in the M10 is grounded with a pice of bare wire. Is your scope grounded? I can see in one of your pictures the usual US plug with only 2 terminals... Here are some screenshots of my measurements. https://photos.app.goo.gl/8YSbaAxZBuXu5rjC2 Pictures: 1) CLK pin 37 of the 8085 2) Pin 7 of the 8085 3-4) CS Pin 20 of the ROM it seems to cycle over and over 5) Reset * at power on VEE is 4.9V V across the battery is 4.02 when the unit is on and 3.9 when off Tomorrow I'll continue hoping Brian or some of you can confirm/compare some of my measurements. Have a nice day Ciao Mauro NOTE: I think I will measure all the pins on the system bus so anyone with an oscilloscope can do the same without opening the unit case... On Dec 11, 2017, at 9:28 AM, Fugu ME100 wrote: > Ah the “special tool” requirement always hated to see that in any step….. > > What did the –5V measure on the meter? If it is not within spec neither the > LCD or buzzer will work. > > From: M100 <[email protected]> on behalf of Brian White > <[email protected]> > Reply-To: <[email protected]> > Date: Sunday, December 10, 2017 at 11:30 PM > To: <[email protected]> > Subject: Re: [M100] Fwd: Re: diagnose > > 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 > >> > >> 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://photos.app.goo.gl/K1AIj3Pmt15xXfR72 > >> > >> > >> -- > >> bkw > >> > >
