Thank you Fugu and Brian for the feedback. Yes I tried the beep BASIC test with no luck and also the cold start (the M10 and the M100 are almost identical...).
I made few other measurements trying to replicate what Brian is doing and for sure the unit is in a loop... In the linked google photo album I added another picture (the first one) showing the ROM CS (Pin 20 yellow trace) and the IO/M of the main processor (Pin 34 blue trace) https://photos.app.goo.gl/8YSbaAxZBuXu5rjC2 As you can see at the beginning of the repeted sequence, I get only 5 pulses on the IO/M The strange thing is that there is so little activity on the RAM CEx (chip enable), like nothing is loaded. Finally I measured also the CSx (chip select) on the LCD connector and none are moving, confirming that on the LCD nothing can be displayed. Mauro On Dec 13, 2017, at 7:01 AM, Fugu ME100 wrote: > Vee at –4.9V is good. > > You may have already looked at these options, so apologies if you have… > > The repetitive nature of the ROM CS cycling could be the CPU in a software > loop waiting for keyboard input. Have you tried the BEEP test from BASIC to > see if the motherboard is actually running? > > Have you tried a cold start? On the M100 press ctrl+pause while powering on, > not sure about the M10. It could be the memory is corrupted with the loss of > backup power. Always a good idea when first powering after switching off/on > the backup power.. > > > From: M100 <[email protected]> on behalf of Mauro Pintus > <[email protected]> > Reply-To: <[email protected]> > Date: Tuesday, December 12, 2017 at 5:24 PM > To: <[email protected]> > Subject: Re: [M100] diagnose > > 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 >> >> >> > >
