Cumana reborn issue

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tgrimwood
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Cumana reborn issue

Post by tgrimwood » Thu Mar 26, 2020 9:42 pm

I have recently bought a lovely new Cumana reborn drive. Upon turning on the device, whilst it is connected to the Atmos, the Atmos crashes as per the pic. I can't get the drive to load a game. Is this a power issue and if so, what is the resolution? I have a new 2amp power supply, and the original Oric power supply too. I have used them separately and swapped them over, to no avail. I am going to try using the new supply, with a 3-way splitter to see if that resolves the issue. I would be grateful for any suggestions.
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Dbug
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Re: Cumana reborn issue

Post by Dbug » Thu Mar 26, 2020 9:43 pm

I wonder, could playing with RV1 at the bottom of the Oric help?

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Re: Cumana reborn issue

Post by tgrimwood » Thu Mar 26, 2020 9:50 pm

Dbug wrote:
Thu Mar 26, 2020 9:43 pm
I wonder, could playing with RV1 at the bottom of the Oric help?
I'm not very technical. Although I have had this Oric since new, I only ever played games. Could you elaborate on what you mean please, and what that would achieve? Thanks.

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Re: Cumana reborn issue

Post by Dbug » Thu Mar 26, 2020 9:54 pm

viewtopic.php?f=8&t=1968&p=19721&sid=50 ... e1a#p19721

I remember that the Microdisc, sometimes would display a message "Please adjust RV1", so you would have to use a tiny flat screwdriver and pass it through the hole at the bottom of the case to adjust some resistor, resulting in the disk drive being happy.

Now, what that does exactly, I've no idea :D

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Re: Cumana reborn issue

Post by mikeb » Fri Mar 27, 2020 4:49 pm

Dbug wrote:
Thu Mar 26, 2020 9:54 pm
viewtopic.php?f=8&t=1968&p=19721&sid=50 ... e1a#p19721

I remember that the Microdisc, sometimes would display a message "Please adjust RV1", so you would have to use a tiny flat screwdriver and pass it through the hole at the bottom of the case to adjust some resistor, resulting in the disk drive being happy.

Now, what that does exactly, I've no idea :D
Note: I don't think it's RV1 on ORIC you need to adjust -- the two controls under Oric are for the frequency for the 4.4MHz colour signal (for PAL UHF output) and for bias for the DAC used to convert output of the video PROM into an analogue signal.

There's an RV1 under/inside a Cumana and similar interfaces. Its job is to adjust the timing when the disc interface writes back onto the bus. What happens is that when the timing is wrong, the disk interface puts data on the data bus at the wrong time, and it stomps on the ULA's use of the data bus, corrupting the image (as shown) ... (if it's a little bit wrong, that is. If it's very wrong, it will stop Oric booting at all).

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Re: Cumana reborn issue

Post by kenneth » Fri Mar 27, 2020 6:09 pm

The potentiometer seems to be used to adjust the delay of the signal on MAP which authorizes the use of hidden RAM, it is necessary to make restarts with a slight rotation of a few degrees each time ...

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Re: Cumana reborn issue

Post by Dbug » Fri Mar 27, 2020 6:17 pm

I stand corrected, thanks :)
So yes indeed RV1, but on the controller board instead of the Oric.
The question is: Does Cumana Reborn have such an adjustment?

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Re: Cumana reborn issue

Post by tgrimwood » Fri Mar 27, 2020 9:11 pm

mikeb wrote:
Fri Mar 27, 2020 4:49 pm
Dbug wrote:
Thu Mar 26, 2020 9:54 pm
viewtopic.php?f=8&t=1968&p=19721&sid=50 ... e1a#p19721

I remember that the Microdisc, sometimes would display a message "Please adjust RV1", so you would have to use a tiny flat screwdriver and pass it through the hole at the bottom of the case to adjust some resistor, resulting in the disk drive being happy.

Now, what that does exactly, I've no idea :D
Note: I don't think it's RV1 on ORIC you need to adjust -- the two controls under Oric are for the frequency for the 4.4MHz colour signal (for PAL UHF output) and for bias for the DAC used to convert output of the video PROM into an analogue signal.

There's an RV1 under/inside a Cumana and similar interfaces. Its job is to adjust the timing when the disc interface writes back onto the bus. What happens is that when the timing is wrong, the disk interface puts data on the data bus at the wrong time, and it stomps on the ULA's use of the data bus, corrupting the image (as shown) ... (if it's a little bit wrong, that is. If it's very wrong, it will stop Oric booting at all).
If it is that, is there anything I can do to rectify it myself?

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Re: Cumana reborn issue

Post by mikeb » Sat Mar 28, 2020 5:53 pm

tgrimwood wrote:
Fri Mar 27, 2020 9:11 pm
If it is that, is there anything I can do to rectify it myself?
Adjust it! :)

VR1 is supposed to adjust a monostable (delay) which delays a copy of the Oric 1MHZ clock.

According to notes on the Cumana schematic, it is intended to create a signal that is 150ns *ahead* of the Oric clock signal, so that some slow piece of hardware can get it's thing done in time and data placed on the bus correctly.

However, it is not possible to create a signal *ahead* of an input, so it actually triggers off the previous clock cycle edge, to give the illusion of "leading by 150ns". This only works because the clock is a regular repeating signal.

Without test equipment to observe/measure the timing, the best thing you could do is move it a small distance clockwise (or counter-clockwise), and see if things improve. There will be a range where it works, outside of that range, it won't work. Put it in that range and leave it alone.

Note it's best to do this once Oric/Cumana have been switched on for a while and warmed up, in case there is any drift with temperature.

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Re: Cumana reborn issue

Post by tgrimwood » Sat Mar 28, 2020 6:01 pm

I believe I have resolved the issue by using a new 2amp power supply and 3-way splitter connected to everything at once.
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Re: Cumana reborn issue

Post by kenneth » Sat Mar 28, 2020 6:27 pm

That's better!! 8)
The difficulty is the simultaneous start of the units to avoid crashing any of the units. Three-way power is a good solution.
PS: The photo is very good, it could have illustrated a computer magazine of the 80s...

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Re: Cumana reborn issue

Post by Steve M » Sat Mar 28, 2020 6:59 pm

Bazinga.

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Re: Cumana reborn issue

Post by tgrimwood » Sun Mar 29, 2020 4:34 pm

kenneth wrote:
Sat Mar 28, 2020 6:27 pm
That's better!! 8)
The difficulty is the simultaneous start of the units to avoid crashing any of the units. Three-way power is a good solution.
PS: The photo is very good, it could have illustrated a computer magazine of the 80s...
Imagine if we had that technology and quality of games in the 80s!

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