Just sharing some info that might help someone here.
I'm a little particular when it comes to powering my precious 8 bit machines with old power supplies. The Atari power supply pictured below was one of the first types distributed with Atari machines in Australia during the early days. There is also an identical looking one that goes with the c64. The only good thing about these is that they're rebuildable. Besides there being no mains fuse anywhere they utilise a very simple circuit and a 7805 linear regulator which runs very hot ( even with a heatsink ) and is very inefficient.
Two things have to go. The voltage divider ( two resistors ) and the voltage regulator. I also remove the large cap temporarily to test it before putting it back in. At the time of writing I realise that I don't need the smaller cap on the output so I'll remove this later once I get my fuses.
There is a little trimpot on the module. You'll need to turn it anti-clockwise quite a bit before the voltage starts to change. I adjust the voltage to just over 5v because I know it's going to drop under load slightly.
I've been fairly busy working on a DRAM & Basic ROM tester for 64kb Atari systems. This is really my first attempt at writing any 6502 for the Atari but I wanted to start off with something simple before I started porting some c64 games to the Atari. It gives me a chance to learn more about the hardware. I've finished testing in MAME and Altirra and I am currently testing this on real hardware to catch any last minute bugs or make improvements before I release it... for free of course.
This program installs in the OS ROM socket and is used as a means for testing the DRAM and Basic ROM. If you have some spare 27c128s lying around then this can easily be installed.
I've currently purchased a few different systems to test my program in. But I might need some help from someone to test in an A800XLF system if I can't get my hands on one.
What it does.
Performs data line integrity checks ( checkerboard and inverse, walking 1s and walking 0s, 1s and 0s and exhaustive )
Exhaustive takes the longest and is probably overkill.
Tests 0x0-0x7ff first to test integrity of the stack and lower mem before using it.
Copies the program rom into DRAM once the above memory verified good.
Turns the OS ROM off then tests the DRAM 0xc000 - 0xFFFF.
Displays bit pattern / test being performed written to DRAM ( also useful for verifying video hardware / PMG ).
Plays sound to indicate CPU is functioning ( for systems playing blind ).
1. Code for address line integrity ( walking 1s/0s ) checks are in but are currently not being used, this will be added in a later version of its feasible and necessary.
2. Write a version for stock 600xls or adapt the current image to handle those systems.
3. Look at writing a version for the Atari 800 for stock 48k systems.
4. Add another indicator / arrow to point out which memory region is bad.
5. Any other suggestions ?
Here is a video of an example of bad ram and bad basic rom.