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juicylemon
March 17th, 2014, 06:16 AM
I am about to receive an Oric-1 which has RGB video and RF output. The problem is that I do not have a monitor that accepts RGB input and I do not have a tv with scart or rf input. I do have a commodore monitor with composite in. Does anybody know if there is a composite signal somewhere inside the oric 1 that I can use?

ChrisCwmbran
March 17th, 2014, 06:38 AM
From this thread here:

http://forum.defence-force.org/viewtopic.php?f=9&t=186

it sounds like there are probably ways of achieving this. One of our members, Carlsson is involved in the thread, so hopefully he can respond and shed more light on this!

carlsson
March 19th, 2014, 02:47 AM
I'm not sure how to get composite video from an Oric. As far as I remember, they output varying signal strength depending on batch and model. I seem to recall even getting a SCART RGB output was a bit of a fiddle with lots of capacitors and stuff just to stabilize the signal. Some of the newer, French made (?) Oric-1's or if those were Atmoses apparently output better signals than the early UK models do but I might might be wrong about this.

The composite video hack as described in the thread might fail if the signal going to the RF modulator is too weak to be used as composite video input to the monitor, it might be enough for the RF modulator to work with. I have read about this for a number of other home computers and video games, that you can't always expect that the RF modulator is fed a nice 0.7 Vpp (or if it should be 1.0 Vpp) signal that you can tap. Even the ZX Spectrum might be on the verge for this hack to work, depending which monitor or TV you use in the end, but usually it works fine.

Which Commodore monitor do you have, an 1702, 1802 or 1902? I suppose in theory there probably are RGB to composite converters, whether they work well with the signal levels output from the computer or not is to find out.

jltursan
March 20th, 2014, 12:06 AM
As carlsson already told you, the Oric video signal is very weak. Although it only need the usual mod, it must be not enough to feed a good composite video signal to you monitor.
You can try with the standard amplifying solution (transistor, capacitor & resistor); but probably you'll end in need of a powerful amplifier (AD724 maybe?)

juicylemon
March 20th, 2014, 10:47 AM
Ok, thanks. I just tried to use the signal without amplification and this is the result:
17885
Does this mean that the signal is to weak, or is something else wrong?

vwestlife
March 20th, 2014, 12:16 PM
Ok, thanks. I just tried to use the signal without amplification and this is the result:
17885
Does this mean that the signal is to weak, or is something else wrong?

Looks like the video signal is fine, but the computer is stuck in a reset loop or has some other problem.

juicylemon
March 20th, 2014, 01:34 PM
Thank you for the hint! I read that the 5V line should be stable before the reset. I used the switch on a power supply to turn the otic-1 on and that caused the problem. The oric works if I turn on the power supply before I connect it to the oric. My Oric is modded It has a switch and the two memory chips has been replaced. Furthermore an extra Rom has been added. I can switch between "Oric extended basic V1.0 1983 Tangerine" with 47870 bytes free and "Oric Extended Basic v1.2 1984 Tangerine" with 37631 bytes free. Does anybody know what the intention of this mod is, apart from the memory upgrade? Originally it was an 16k Oric-1.

carlsson
March 21st, 2014, 12:07 AM
Well, you can change ROM version. The early ones 1.0 and perhaps 1.1 were quite buggy, which is one of the reasons why the Oric Atmos was released. It uses the same motherboard, but with newer ROM version, a case in black and red instead of white and a keyboard with real keys. The Atmos has 64K out of which 48K are usable for programs, I believe the other 16K shadowed behind ROM is used for floppy drive controller ROM. So as far as I can tell, by toggling the switch to 1.2, your Oric would rather be Atmos compatible, in particular if the RAM chips also have been upgraded from 16K to 64K.

jltursan
March 21st, 2014, 12:14 AM
Nice, the 1.0 ROM is the Oric-1 original one, full of bugs. It was promptly replaced with the one in the Atmos, version 1.1.
The ROM 1.2 is a hack done by Pascal Leclerc (http://pleclerc.free.fr/Oric/OricPage.html) with some enhancements over the old 1.1 version.

About the memory, there's no upgrade at all. You've the standard 48K RAM; but the buggy Oric-1 1.0 ROM reported video RAM as user RAM, that's why it shows so much memory. Since ROM 1.1 it was corrected and the startup message display the correct amount of memory :-)

juicylemon
March 21st, 2014, 03:46 AM
17892
17893
These are pictures of the board. It has two D4146C RAM IC's
From the back it looks like these have been hand soldered on the board for this mod. Also the socket for the second ROM and the 74ls00n below the speaker have been soldered on. I'm not sure about the sound chip and the resistor that goes across it.

jltursan
March 21st, 2014, 05:30 AM
Way cool!. You have an original 16KB model upgraded to 64KB. The RAM ICs can't be seen clearly; but they must be a pair of uPD4464. That's why they look hand soldered, IC11 aswell.
Both ROM sockets have been filled and the usually empty second socket is occupied with the old Oric-1 ROM. I think it's better to use a bigger EPROM (27256) and burn both ROMs, then you can use a switch to select the active ROM (after doing some mods to the EPROM).

The other mods in the back of the motherboard look like the mandatory service bulletin mods, mostly designed to improve reliability of the Oric-1.

As you have the PCB now, it looks extremely close to what a Nova 64 PCB looks like. The Nova 64 is a extremely rare Atmos clone built in Yugoslavia.

juicylemon
March 21st, 2014, 07:17 AM
I think it's better to use a bigger EPROM (27256) and burn both ROMs, then you can use a switch to select the active ROM

Why is that better? Because I can already switch between the ROMs

jltursan
March 22nd, 2014, 04:35 AM
Just a matter of taste: less crowded PCB, less drawn power if you choose the right IC and this way you can go for an even bigger EPROM/EEPROM and burn four ROMs (1.0, 1.1, 1.2 and diagnostics ROM) :-)

juicylemon
March 22nd, 2014, 05:45 AM
Ok, I understand, but I think I'll leave it like this and enjoy this computer as it is for now :)