The computer was returning an inconsistent quantity of free RAM, indicating one or more chips was bad.
I disassembled the system in order to access the RAM. I positioned the disassembled OSI Challenger's motherboard so that I could test components while powered / live system. View working disassembled
As you can see from the pictures, the system needs some cleaning.
First I replaced the inconsistent RAM until the system returned "7423 Bytes Free" when first booting into BASIC every time.
Next I carefully photographed all of the mods done to this system (factory or owner?), in the event that a brittle solder connection comes lose and requires repair.
J3 Connector (Modem/RS232) 2 3 4 5
J4 Connector (Joystick)2 3
Cassette baud 300/600 switch 1 2 3 4 5 6 *
* Note that the orange and brown wires in the photos are not part of the mod, these wires are used to power the "on/off" light.
After the system checkout, I proceeded to write a simple BASIC program and store it to tape. Worked, good. I also loaded RAM test program I found to test the RAM. No errors found, good.
To load a cassette:
enter BASIC and then type LOAD (but don't press Return yet). Position the cassette to the beginning of the program and press play on the cassette player. Hit Return.
I have my volume turned to 7 with tone set to 9.
The program will actually show the BASIC listing on the screen as it's loading. If you see errors in the program entry (missing / misprinted line numbers for example), adjust the volume or tone until you get a consistent result. If you see a bunch of garbled characters before the program listing appears on the screen, don't worry as long as they stop before the first line of BASIC code appears. If ALL you see are garbled characters and the BASIC program listing never materializes, you may have a bad tape/player.
When the load is done ignore the syntax error warning at the end of the loading process. Hit "SPACE" and then "Return". Stop the tape.
If the program loaded correctly type RUN and Return.
More / Updated Photos