shoestring

The firing sound in Dropzone on the Atari 800 is iconic IMO, makes the game so much more enjoyable. Although it's obviously very Defender-esque if you compare the sound effect from the arcade, the c64 version firing sound pales in comparison.

Thanks. I'd say you still have a partially bad RAM chip(s) within the first 64kb of addressable memory. But you might want to check the MMU whilst your at it as emphasized by others. Some bits will fail verification at specific addresses and not necessarily at every address. But from experience these DRAM chips tend to fail completely, most likely due to some faulty power supply or as someone here once put it... a "Commodore attack" ( the act of trying to use a C64 power supply in an Atari 8 bit).

Mine is still far from perfect but what do ya expect for free . For instance it's accurate for partially bad ram, depending on where the fault is. Today I was testing some ram chips from an aux 80 col card for an Apple II, I knew one or more were bad..the built in Apple IIe diagnostic was giving me different results each time I powered up, its usually great for testing the RAM on the motherboard through. After installing those two 4464s from the 80 col card into my XE, it was able to identify U9 as the culprit and did it consistently. When I swapped the two around in the XE it told me u10 was bad. I wanted the ability to test 4464, 4164 ram chips easily. I also aimed at making something that would display a picture on the screen even with no RAM installed in the machine at all, as long as the vital components in the machine are OK... you should always see something.. even if the screen flickering like mad. Sys-check should be much more reliable because I believe it has it's own work ram on the cart.

I've personally known someone who lived next door exchange their c64c several times before they got a reliable one ( machines exchanged stopped powering up after a week or two ) that survived the summer holidays in 86. All of them came with the white brick with the embossed chicken head logo and potted inside. So given they were new and those problems existed back then... the only suitable use would be as a doorstop.

You could also go a step further and type in this basic program which copies the character set from the character rom to the RAM. https://www.devili.iki.fi/Computers/Commodore/C64/Programmers_Reference/Chapter_3/page_110.html 5 PRINTCHR$(142) :REM SWITCH TO UPPER CASE 10 POKE52,48:POKE 56,48:CLR :REM RESERVE MEMORY FOR CHARACTERS 20 POKE56334,PEEK(56334)AND254 :REM TURN OFF KEYSCAN INTERRUPT TIMER 30 POKE1,PEEK(1)AND251 :REM SWITCH IN CHARACTER 40 FORI=0TO511:POKEI+12288,PEEK(I+53248):NEXT 50 POKE1,PEEK(1)OR4 :REM SWITCH IN I/O 60 POKE56334,PEEK(56334)OR1 :REM RESTART KEYSCAN INTERRUPT TIMER 70 END Once, you type in the above listing and run it, then type the following statement to tell the VIC II to fetch the glyphs from ram. POKE 53272,(PEEK(53272)AND240)+1 List the program or type some stuff on the screen, do you still see tearing on the bottom half of the screen ? In some cases character rom can go bad and glyphs can have additional artefacts or missing pixels, so you can also change the letter T to some other shape to confirm that. In your case, I'm confident that the character rom and ram is OK. 10 FOR I=12448 TO 12455: READ A:POKE I,A:NEXT 20 DATA 60, 66, 165, 129, 165, 153, 66, 60

Looks like a bad counter somewhere in the video circuit, could be the VIC II. Is your machine socketed and does this also affect sprites or only character objects ?

From 2016 but still interesting if you haven't seen it before. http://www.pouet.net/prod.php?which=67366

Was definitely the first computer I ever used, I believe a non enhanced IIe from 1983. I was in third grade. Wanted one but we could never afford one. First program I ever used was the Apple IIe Introduction on disk and favourite game at the time was Choplifter. Favourite all time Apple games were Karateka, Lemonade stand, Where in the world Carmen Sandiego ,Swashbuckler and Aztec. Neighbour had a TI, so we played that. I vaguely recall using an 800xl on display at a K-Mart which was running basic but there was also a c64 right next to it running BC Quest for tires. We ended up with a c64 but I always loved using the Apple in school as well and I was constantly dropping into the built in machine code monitor and messing around with the 6502 instructions.

Hi Graeme. Been following your posts on eab and YT updates since Bombjack. Nice to see you here.

Don't you mean c50? Try a polymer solid electrolytic cap ( more reliable ) if you know c50 is bad. It's not rare for those to fail, just search the forum and you'll come up with some results. But I think you'll get better results if you try a proper 5v power supply.

They can and they will, switch mode is inherently very noisy. They're not suitable for continuous use because they're not designed to filter switching noise sufficiently, all they need to do is charge. I'd say your filter needs a tweak. I used a DC-DC buck module in a power supply that I rebuilt which has some filtering but I could still see 150+mv of AC ripple on the 5v line under load, added an additional low ESR capacitor and a choke brought that noise down to around 30mv and cured the jailbar effect.

Saw one for the first time in a shop window late in the evening on the main street in my city. It was an Amiga 1000 with the monitor facing the shop window and there was a fixed digitized image of a red Ferrari on the screen. I'll never forget it, I stared at that image for about 5 minutes in amazement before being pulled away by my parents. I couldn't believe what I was seeing because at the time, PCs were still using EGA graphics and my c64 had similar limitations. From that point on I had to have one but the A1000 was too expensive, we eventually got an A500 with 1.3 in 89 or 90 and the first game we bought was Shadow Of The Beast II, it was $79 which was really expensive in 1990. My brother loved playing Sensible Soccer and Kickoff where as I loved playing Hybris and Silkworm. I had a friend over all the time and we'd watch the latest demos and read all the scene disk mags, he loved downloading protracker mods and would have them playing in the background whilst looking at stuff on the internet. I don't have an Amiga anymore, they are just too expensive to maintain and keep up to date. But I'm still doing a lot of assembler programming in vasm and mess around in UAE. Currently playing around with gfx in mame, dumping them and implementing tilemaps via the copper/blitter. Amiga was a great system, unfortunately it wasn't very well balanced. AGA wasn't much of an enhancement in 92, it was fairly pointless without an upgrade of the blitter or at least a tilemode in hardware.

Dave Haynie was designing the next system architecture in such a way that make would make the next system more modular. That is, separate the graphics from the audio and then I/O. He designed a custom bus that would solve those problems however, PCI came out which solved that problem and did it much better than he did. Commodore actually loved to use standards as long as they weren't rubbish. The next generation Amigas would have had a PCI bus, graphics would have lived on PCI and there would have also been a PCI to Zorro III bridge. Dave had already speced out PCI interface to AA and AAA so the gfx would have lived on a card eventually.

I have one of those PAL International NTSC models. I recently converted it to NTSC to get colour by swapping the crystal and IOU. My write up is here for those interested https://www.jammarcade.net/apple-iie-enhanced-platinum-ntsc-50hz-to-60hz-conversion/

Yes, bin it while you still have a working machine.

Maybe you can use this type of SRAM on a daughterboard to replace the 4 bit rams in the 600xl and XE machines. It's for the c64 but I can't see how this wouldn't work in an Atari computer.

So many possibilities ( mmu, cpu, osrom, ram, 74LS logic ). Maybe even a single bent pin hiding between the top of the socket and bottom of the chip. Do you have any carts to try in the machine ? ( star raiders ).

You can build this overvoltage circuit below for relatively cheap. I modified my Atari and C64 power supplies using a variation of this circuit which introduces a voltage clamp and fuse on the 5v output. http://www.electronicecircuits.com/electronic-circuits/7805-5v-1a-regulated-power-supply-with-overvoltage-protection-circuit Instead of the 7805 I used a DC-DC module and adjusted its output to around 5v, then trimmed the board to fit inside the case. Most of the parts are hidden under the DC module but it's essentially the same circuit. The only changes I made were to the zener diode value from 6.2v to 5.6v and I also added a choke ( not pictured here ) to reduce the switching noise exposed on the 5v line. Winding the pot on the module past 5.7v blows the 2a fuse and protects my machines. Have been running this setup happily for about a year now with no problems. You could also use a TPSM84205EAB, which is a drop in replacement for the 7805.

Only because I disagree with "Macintosh Color" more than Apple II.

I remember Bil Herd saying that they had a warehouse full of those machines but it's unclear where their final destination was.

Arguably it was 3 computers in one with a Z80A or B and could run CP/M, albeit rather slow compared to most other CP/M systems.

The 555 timer is part of the reset circuit, so if it's broke the CPU will just sit there waiting for a RST pulse with its outputs stuck. But I don't think that's OP's problem.

I had the opposite problem with the same result as expected. NTSC 800 and a Commodore 1084S-P1 ( PAL ). So a black and white picture is normal. To solve this I use a Sony PVM 9", which handles both NTSC and PAL.

The ones I've seen all look like re-branded PALs. The ones I have in-front of me are MMI re-branded with c061618 instead of PAL16XXX with date codes around 83. GALs weren't introduced until 1985 but you might be able to find one in an XE? And here is one manufactured by National Semiconductor.