07-09-2013, 09:00 PM
Another oddity from the early 80s, the Oric 1 had like the Sinclair machines the distinction of being UK designed and built. The company in question, Tangerine, named themselves as such to be on a par with Apple! Their first computer was the Microtan and the Oric 1, then latterly the Oric Atmos (an Oric 1 with updated ROM and keyboard) were released onto the market before the great Christmas Computer crash of 1983.
The Oric's were on the face of it reasonably thought out with proper connectors, a centronics port, dedicated monitor output as well as UHF, and the usual tape port along with an interface connection point. The let down in this case was the keyboard, a chicklet type that was corrected in the Atmos. However, much to Tangerine's shame, the ROM was buggy on the Oric 1 and the same bug was carried over to the Atmos.
This example that came across the workbench was an issue 3 fitted motherboard with 48k RAM being run by a 1mhz 6502 processor. Documentation is reasonably easy to obtain off the internet and an hours research downloaded the service manual. Inside was reasonably clean and tidy with no rot. Some bending of the pins on the centronics port and an external glut of dirt to clean off. The power supply has a nasty gold coloured cap, 4700uf 25v, which was replaced as a matter of course. Plugging in and connecting to a monitor showed a major issue with the UHF output with the image being double screened and fluttering with a grainy overcast. Nothing appeared out of place so a feed from the composite supply to the Astec block was taken but still showed the same image issues. The Oric uses a dedicated ULA to generate RGB + Sync which is them branched, one via a buffer to the monitor output port, the second to a RGB to Comp convertor using a dedicated PROM to do the honours. RGB quality was fine so that ruled out ULA failure, which meant delving into the fine vulgarities of the composite - UHF stage. Supply volts to the five chips was fine, nothing was overheating, the xtal ref freq was bang on target.
Picture quality and balance is done via a basic potential divider circuit, with variable resistor RV1 adjusting the picture quality. The service manual provided a nice clue, twist RV1 one way and the white becomes yellow, twist the other way and the screen will display the sort of issues being displayed. Tapping around RV1 with the blunt end of a screwdriver made the image on the screen jump badly, could RV1 actually be faulty, it was an open skeleton type after all and subject to corrosion. A jet of contact cleaner and movement of the wiper suddenly cleaned up the quality of the output to an acceptable level with all ghosting removed. RV1 is earmarked for replacement once I find a suitable replacement in stores, it appears the carbon track is literally turning into dust. Test operation of all computer functions reveals a fully working Oric 1 machine.
Photo 1: Oric 1 keyboard.
Photo 2: Motherboard
Photo 3: Close up of video generation chips and RV1 preset
The Oric's were on the face of it reasonably thought out with proper connectors, a centronics port, dedicated monitor output as well as UHF, and the usual tape port along with an interface connection point. The let down in this case was the keyboard, a chicklet type that was corrected in the Atmos. However, much to Tangerine's shame, the ROM was buggy on the Oric 1 and the same bug was carried over to the Atmos.
This example that came across the workbench was an issue 3 fitted motherboard with 48k RAM being run by a 1mhz 6502 processor. Documentation is reasonably easy to obtain off the internet and an hours research downloaded the service manual. Inside was reasonably clean and tidy with no rot. Some bending of the pins on the centronics port and an external glut of dirt to clean off. The power supply has a nasty gold coloured cap, 4700uf 25v, which was replaced as a matter of course. Plugging in and connecting to a monitor showed a major issue with the UHF output with the image being double screened and fluttering with a grainy overcast. Nothing appeared out of place so a feed from the composite supply to the Astec block was taken but still showed the same image issues. The Oric uses a dedicated ULA to generate RGB + Sync which is them branched, one via a buffer to the monitor output port, the second to a RGB to Comp convertor using a dedicated PROM to do the honours. RGB quality was fine so that ruled out ULA failure, which meant delving into the fine vulgarities of the composite - UHF stage. Supply volts to the five chips was fine, nothing was overheating, the xtal ref freq was bang on target.
Picture quality and balance is done via a basic potential divider circuit, with variable resistor RV1 adjusting the picture quality. The service manual provided a nice clue, twist RV1 one way and the white becomes yellow, twist the other way and the screen will display the sort of issues being displayed. Tapping around RV1 with the blunt end of a screwdriver made the image on the screen jump badly, could RV1 actually be faulty, it was an open skeleton type after all and subject to corrosion. A jet of contact cleaner and movement of the wiper suddenly cleaned up the quality of the output to an acceptable level with all ghosting removed. RV1 is earmarked for replacement once I find a suitable replacement in stores, it appears the carbon track is literally turning into dust. Test operation of all computer functions reveals a fully working Oric 1 machine.
Photo 1: Oric 1 keyboard.
Photo 2: Motherboard
Photo 3: Close up of video generation chips and RV1 preset
