Microdisc Service Manual

If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
How to program the oric hardware (VIA, FDC, ...) is also welcome.
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Chema
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Re: Microdisc Service Manual

Post by Chema »

Problems with random chars on the screen, not booting, faulty loading, etc. are usually related to the MAP signal and the problems with the Oric expansion bus signals. An amplibus may correct those (almost always does), but I've noticed that some flat cables are more error prone.

If your interface works with a Gotek, but not with a real floppy, maybe there is more noise, or the PSU is not able to give enough current or a good 12 volts to feed the floppy drive (some old units need 12v, newer 3.5 drives don't).

But this is just a possibility... may be another totally unrelated problem.

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Vyper68
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Re: Microdisc Service Manual

Post by Vyper68 »

Steve M wrote:
Wed Sep 09, 2020 4:35 pm
If you measure between the middle leg and the one nearest to RV1 on the board I'm getting .925.
Make sure you have this little wire in place.
Hi Steve can you post a picture as the whole of the underside of the Cumana PCB please. I hadn’t fitted the wire so that maybe why it’s hanging, but I can see possibly another in the top right under the power wires.
As far as power goes I substituted the 10v transformer with a 9V 2A centre negative psu to match the polarity going into the board and 7905 regulator on the board. The lead going into the Oric comes off the power rails before they go into the 7905 with the wires reversed to change the polarity to centre positive. I just tried to replicate what I saw without having access to a transformer. I dropped it down to 9V from 10V as the heatsink I had fitted to the 7905 was getting hot trying to dissipate the excess power.
Bazinga!

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Steve M
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Re: Microdisc Service Manual

Post by Steve M »

I'm going to have another look at it later. I don't think there is another wire. It may be a bit of resoldering that you are seeing.
I have to do some more testing swapping power supplies for the drives to see if the Opel will fire up then. It's a bit difficult as my system sits under the monitor, so call the cables stop things from being easily moved.
I really need to get a 3" drive working so I can check some of those disks and move some software onto 3.5".

Has anyone repaired a 3" drive?

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