On Mon, Dec 3, 2018 at 11:00 PM Mauro Pintus <mau...@tiscali.it> wrote: >
> > Checking some signals with the oscilloscope it looks like it is looping after > a fix time without completing the boot. > > Francesco Messineo (another user of this list) wrote me in this days to offer > some help and he suspect I damaged the RAM. Thank you again Francesco. > I bought a desoldering iron and I hope in the next few days I'll find the > time to try removing all RAM modules and fit one at a time in the first > socket (hoping one module is still alive). I actually suggested the RAM could be damaged when he opened SW3 (the RAM backup power) with SW5 (the main power switch) closed is that some logic and the RAM have Vb as Vdd rail and almost the rest of the system has Vdd derived from Vp (via the dual output inverter). Now, if you look at the schematic, SW3 removes both Vb and Vp, but, on Vb there's only a few bypass capacitors to ground plus 1 uF electrolytic, so it might discharge quickly, while on Vp there's at least one 470uF capacitor plus another 470uF on the output of the inverter on Vdd side (yes, also much more logic powering from it, but stil...). What might happen in this case is that the Vb got quickly to 0V with still some inputs of the chips powered from it have something like +5V applied; in this case, the protection diodes on the input start conducting and some of them might get shorted or degraded from this current. It happened a few times on logic that I designed that had a backup power for CMOS RAM, I had to make sure that all inputs to the RAM were either following Vbackup or already switched to logic 0 before removing the backup power. So in this situation I would examine all the logic powered directly from Vb and that includes the RAMs. Usually a quick test with a multimeter (with all circuits powered off) from each input pin to Vdd pin of the chips can show if there's some damaged input protection diode. HTH Frank IZ8DWF > > > > Sent from my iPad > > On 03/dic/2018, at 19:06, Jan Vanden Bossche <jan80...@yahoo.com> wrote: > > Mauro, > > What do you need to repair your M-10? > > Greetings from the TyRannoSaurus > Jan-80 > > > ________________________________ > From: Mauro Pintus <mau...@tiscali.it> > To: m...@bitchin100.com > Sent: Saturday, 1 December 2018, 16:12 > Subject: Re: [M100] Olivetti M-10's for a new home > > Thank you Jeff, really appreciated. > Now I keep my finger crossed :) > > Have a nice day > > Mauro > > > > On Dec 1, 2018, at 3:59 PM, Jeffrey Birt wrote: > > Mauro, > > You have a need for them, so you should have them if the original person does > not speak up. Fixing your machine is a better use. I have no specific need, > just thought it would be neat to have a machine with AZERTY keyboard. > > Jeff_Birt > > From: M100 <m100-boun...@lists.bitchin100.com> On Behalf Of Mauro Pintus > Sent: Saturday, December 1, 2018 7:50 AM > To: m...@bitchin100.com > Subject: Re: [M100] Olivetti M-10's for a new home > > I was soo exited I didn't see the other answer from Jeffrey, I'm sorry... > Hope we can find an agreement, I'm really interested but I don't want bother > anyone. > > Mauro > > > > On > > > >
