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Vyper68 wrote: ↑Fri Sep 04, 2020 2:36 pm Yes 11 and 13 were shorted by a tiny bit of solder across two tracks where the solder mask was missing

Ah, it happens! At least it wasn't between the 12v/0v rail on a DIY plugin board in a PC (Switch on, flash, bang!) ...

Don't leave us dangling, does it work now?

That was how I was looking at the RAM. 74LS257 ----------------- RAM IC20 Pin 9 ( MA6 ) Pin 5 ( A0 ) IC20 Pin 12 ( MA7 ) Pin 9 ( A7 ) IC20 Pin 7 ( MA2 ) Pin 6 ( A2 ) IC20 Pin 4 ( MA3 ) Pin 10 ( A5 ) IC8 Pin 9 ( MA5 ) Pin 11 & Pin 13 ( A4 & A6 ) IC8 Pin 12 ( MA4 ) Pin 7 ( A1 ) IC8 Pin 7 ( MA...

To clarify .. The MA lines come from the ULA to the respective pin on the LS257 as per the schematic but the line out from the LS257 to the Address pins on the RAM chips do not go where they should based on the schematic. For example pin 9 on IC20 should be MA6 which should go to pin 13 goes to pin...

Maybe the TSN module starts up a little slower than a 7905 and a snappy power supply, (either just how it is, or a deliberate soft-start feature). Next time you come across this :- 1) Ensure that you are providing a good solid input supply, powered on smartly. 2) When Oric doesn't boot (as you found...

One stupid idea.. Not a stupid idea! Address lines A0-A15 (as on the CPU and expansion port) are not affected by the ULA (ULA only reads A15-A8, and doesn't connect to A7-A0). So activity on any of the address lines indicates running CPU. Although, if the CPU reads "bad code" from memory,...

Tips above about power supply types and order-of-switch on are correct, but all that comes back to the power on reset not working well enough. If the POR worked, a sluggish power application wouldn't matter, Oric would start correctly. As it is, (especially true with the original reset capacitor + a...

Vyper68 wrote: ↑Tue Aug 25, 2020 6:53 pm I’ll get my coat

No no, grab popcorn! Things could get interesting!

any chips I change I always when possible put sockets in to help with future diags Sockets: OK -- just wanting to check the history of the board. As long as you're sure all the traces are good (otherwise you could be on a wild goose chase fixing a faulty component you'll never find. I fully support...

like INK first and then PAPER, to limit the visually lost column used by INK, This is true, of course the normal Oric BASIC screen (TEXT mode) writes PAPER first *then* INK, revelling in the two "lost" columns! I wonder why? Was it to stop people seeing a 39-column screen and thinking the...

if I take ic5 and ic 6 out I get the same screan so it's deff not them also have tested ic7 on friends machine works spot on On this point: Did you find out if IC5 and 6 work in a friend's machine? Or are theirs soldered in, so you couldn't test this :) From the factory, I think the ULA and the ROM...

Hi thanks for that have tryed all your suggestions but I'm even more confused now if I take ic5 and ic 6 out I get the same screan so it's deff not them also have tested ic7 on friends machine works spot on so not that getting 4.9v on the 74lsxx chips so power getting there also tested rom No one s...

You could start here, grab the PDF and the .ZIP pack of images. http://oric.signal11.org.uk/html/repairguide.htm On the plus side you seem to have a stable decent picture, and while that's an unusual arrangement of bars, that could be down to the specific type of DRAM chips used -- at least it's ord...

Not sure if there's much similarity, but I have a schematic and bare-board scans of the Cumana interface here :-

http://oric.signal11.org.uk/files/pub/cumana/

No service manual though.

The thing is that my 27C512 didn't pass the empty test in my programmer. It did however write the binary in, and while verify fails, looking at the file contents visually show that the binary should be in there in its entirety. I don't know if you or the chip-programmer are to blame there ;) If you...

I found that I could erase a UVPROM with an 18w UVC germicidal tube in less than 1 minute. If anyone needs to. Erase or nuke? Did you mount the tube inside the chip ;) ? "The recommended erasure procedure is exposure to UV light at 253.7 nm of at least 15 Ws/cm2, usually achieved in 20 to 30 m...