Oric-1 display problems

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nivrig
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Oric-1 display problems

Post by nivrig »

Hello all. I picked up an Oric-1 recently, saving it from a skip. It largelt works, but it maybe has a few problems and I'm looking for advice on fixing them. For reference I'm using a modern 9v 2A PSU and a powered SCART lead.

On boot from cold, this is the display:
Image

After letting the machine sit powered-up for a few minutes, it will start, but the display is odd. BASIC PEN/INK commands show colours on screen, but there is some background colour flickering and the characters seem to shimmer.
Image

There is also a short (15s, silent) video here to illustrate:
https://imgur.com/iMkqyhZ

Leaving the machine powered on for longer (15m?) improves the display so that it's pretty much perfect.
Image

I tested voltages internally with a multimeter. All the main ICs are getting a good 5v, and none feel overly hot, apart from the 74LS365 IC22 near the RGB port. The meter shows 0v across it's Vcc/GND pins. I'm not an electronics guy so I don't know if this is normal or not.

I know from experience some other machines can have weird warmup problems like this if they have bad capacitors. I noticed a couple of the blue electrolytic caps on the PCB but they look OK visually.

Any suggestions as to what to look at?

Thanks!
nivrig
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Re: Oric-1 display problems

Post by nivrig »

Update: after more experiments, the strange display problems are intermittent and not seemingly related to how long the machine has been on for. It might be the Oric and my monitor randomly not getting along. Removing and reinserting the SCART plug will reset the display to a good picture.

On first cold start the Oric still freezes at the vertical lines screen. I think this is some kind of RAM test? Waiting a few seconds then powering off and on will let it boot.
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Chema
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Re: Oric-1 display problems

Post by Chema »

Which SCART cable are you using? Can you test on another TV? (I guess no)

About the booting thing, the Oric was quite "lazy" on booting. I always had to plug the PSU first, then insert the jack in the Oric and not the other way round. I ended up installing a switch on the cable. What you see (with vertical strips) is common when the Oric does not boot. I've seen this, although it is more common to see the usual "horizontal white bars" pattern.

There was a service modification which tried to improve this behaviour. Check http://www.48katmos.freeuk.com/servman.pdf

But some hardware expert around this site can better tell how to improve this power up sequence.
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Dbug
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Re: Oric-1 display problems

Post by Dbug »

nivrig wrote: Fri Jun 18, 2021 9:23 am Update: after more experiments, the strange display problems are intermittent and not seemingly related to how long the machine has been on for. It might be the Oric and my monitor randomly not getting along. Removing and reinserting the SCART plug will reset the display to a good picture.
I would open the scart cable and check that all the wires are properly soldered, could just be some corroded pin, or a wire connected by just a thread, that could explain the weak sync or color. Bad grounding as well.

For the boot, yes, like Chema said: Plug on the mains first, plug on the Oric after. It's an issue with the reset of the CPU not being long enough, so it gets started before the power is stable enough and basically crashes on startup... which brings the topic of: Put something on the bus connector (styrofoam, sticky-tape, a female IDC connector from an old floppy disk, ...) so you don't mistakenly plug the Oric power on the bus and fry the ram.
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kenneth
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Re: Oric-1 display problems

Post by kenneth »

The scart must be wired with a video cable type, the coaxial insulation is thicker than the audio insulation, to start, you can leave everything plugged in and add a bedside lamp switch on the 9v power cable.
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ibisum
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Re: Oric-1 display problems

Post by ibisum »

Any time I see these kinds of issues with an Oric, the first thing I do is find a reliable power supply - 1.2A at least. Check yours, it may be weaker than you think.
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