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Re: Oric Atmos Won't Initialise

Posted: Sat Mar 30, 2019 10:05 pm
by NekoNoNiaow
Two things come to mind regarding your issue:

a voltage of 4.85V seems indeed a bit low but this is a DC measurement which can hide AC variations. Have you tried measure AC voltage on that line?
If there are no ripples on the 5V rail, then it should show 0V but if there are then you will measure a non zero value which would indicate that indeed voltage is not stable enough.
If that is the case, then components (such as DRAM) may not be deficient but will fail nevertheless (and possibly randomly).

If you indeed find non negligible AC voltage on the +5V rail, then changing any electrolytic cap around before and after the regulator would seem to be in order.
And while talking about caps, have a look at this appendix: (*) ;)

it seems like this issue would be one that could also possibly be investigated using a diagnostic cartridge with its own CPU (and ideally its own power supply) which could drive the bus signals and test some individual components such as DRAM. Are diagnostic cartridges available on the Oric?

Hope this helps,
Cheers. ;)

(*) in general, I would recommend to change all electrolytic caps immediately after acquiring a retro machine.
They are 30+ years old and them not working perfectly anymore can influence normal operations in very subtle and semi invisible ways. By giving new caps to your Oric, you will be able to better diagnose other potential issues later on. And moreover they can leak and damage the board so just do it first thing. ;)

Re: Oric Atmos Won't Initialise

Posted: Sun Apr 07, 2019 6:27 am
by Equinoxe
I agree changing the caps would be beneficial and had ordered them. In the meantime I gave the motherboards to a tech at work and he said he could use his logic analyzer to check for failed components without needing to plug them in (I'm not sure how this is done, it's way above my very basic understanding of electronics).

There's no diag cartridge for the Oric (currently at least) but a couple of ROMs exist if a person has the means to program them (I'm currently researching how to program a 27128 with a Raspberry Pi more as a fun project for the next long Canadian winter :))

Re: Oric Atmos Won't Initialise

Posted: Sat Apr 27, 2019 1:38 am
by Equinoxe
The tech socketed all the chips and changed all major ICs and RAM now the machine is showing the attached pic. Any ideas? Changing RAM with others changes the display colors. Regulator is showing 4.9V at output so going to change that next.

Re: Oric Atmos Won't Initialise

Posted: Sat Apr 27, 2019 2:18 am
by NekoNoNiaow
4.9V is within 2% of 5V and is well into the recommended zone, there should be no need to change the regulator.;)