fauxscot

Three sources of video junk.... one is the busted video chip (it's eating some graphic blocks), another is slightly out of tune RF modulator and the last is probably power supply noise.

Well, I have to tell you... I am not easily impressed but you sir, are a rock star. I cannot believe what you have done! I am sitting here chuckling out loud! My god, what amazing work. You must drop me an email so we can talk more efficiently. Jumping jesus on a pogo stick. Amazing.... F

Pix from this AM: https://www.dropbox.com/sc/vse5gh5719eusha/nR5QQq9nww

News on the multi-cart front... Had to set things aside for a few weeks and deal with other projects, but finally got back to work on it this weekend, late. I have built a composite card that fits in the card slot and takes the place of all the RAM chips and the resident ROM chips. It has been misbehaving and presenting a complicated debug, leaving me uncertain as to what has been going on. It uses one RAM chip and one latch, plus some haywires. Takes a very slight mod to pick up two processor outputs. Sorry for going dark, but what should have been a simple build and test took a lot longer than expected. One reason was that the S2 I was using was not one I had a huge amount of confidence in. I am using a busted video chip, too. And a micro-system troubleshooter which SEEMS to work pretty well, but which was giving me ambiguous results. Finally this morning, I re-checked everything, made a few tweaks and now have an operational Studio 2 running out of a 32K battery-backed RAM chip. This is the first step in making it into a universal card. Right now, it's running RCA code, but doesn't have to. An enterprising lad might write an entirely different 'OS' for it. (That would NOT be me, BTW.) Pix in a minute or two. It's downstairs waiting for me to make the first move in a bowling match. Woot.

So I was working on a few busted units and got 3 of 4 to work. #4 is now the multi-card development platform. After getting one of the units fixed, i boxed it back up in the box it arrived in, duct taped it and headed off to the post office, since i live where there is no UPS store. Decided to ship it first class, as I am a cheap bastard.It cost me EXACTLY $18.02 to mail it. Whack, huh? Anyway, concerning the multi-card. I'm planning to make it universal, but step one is to make it work in basic form. I'm off of it for today, but will work some more over the weekend, I hope. My current card has 32k of memory, more than enough to store all the games, I think. More than enough to support an operating system or monitor, too, except the 1802 does not have a hardware UART for serial IO. It's expensive in software terms, too, and the processor is slow as hell. But in terms of raw memory, the 32K I have installed is a lot of memory, considering that the original has 2.5K, of which 512 bytes is RAM. I have a lot of 32k chips, too, so there is a premium for me to get this approach to work. yesterday morning, when I stopped for the day, I could read and write all locations, and the software was installed but did not work. Today, I can no longer read reliably, but can still write to page 0 with no issues. Not sure why. The 1802 is unusual in that it has a muxed address buss that latches the high order byte first. I have a pile of 87C257 latched EPROMS that latch the low byte first, and is IS POSSIBLE to re-map the contents to make that work, but non-trivial and i think, poor form, so I'm opting for a HC573 or 574 octal latch / octal D-flip flop (either should work), and the DS1644 as a combination program store and RAM. I don't have any spare 1622 SRAMs laying around, and needed to put in some RAM to fix the S2 I am using, so this kills a lot of birds with a single shot. When it works, that is. If it works! If not, on to plan B.

stil working on the multi-card. i've got a 32k ram board made that i'm debugging. contains the system roms, both game roms and the 512 bytes of ram, plus 30K more, give or take. two chips, and they work but not perfectly yet. the idea is sound, and it's just that I have all these battery-backed 32k SRAM modules that has me playing with this. once it works, of course, it works. also cures any S2 that has bad rams or roms. the rams cost $10 a pop and they are available, but i don't have a bag of them like i do the DS1644's. kinda cute. more later. i've been quiet, but not lazy. moving along about as fast as i can push it.

You are the man! Thanks. Good job on the scans, too.

The diode on the 555 circuit is used to provide that non-linearity in the beep, FYI. It was a feature, not a problem!

Thanks y-bot! I appreciate the photos a lot.

For anyone interested, I have been troubleshooting 4 units from two members to get re-acquainted with this thing. One was simple in that it turned out to be misadjusted RF oscillators but otherwise worked OK. Another one was a display chip failure... one bad data line. it was fixed with cannibalizing. The remaining two have 800-8ff RAM problems, but their 900-9ff RAM is good, meaning one of them can be recovered. So 3 for 4... not bad for an old man. I obtained an 1802 pod for a Fluke 9010a micro system troubleshooter and that is what I've been using to test these, as well as normal test techniques based on knowledge of how the unit works. I built a ROM dumper and am working on the multi-card, though I am still struggling with a few architectural decisions before I commit to an approach. This has more to do with part availability than anything, and with consolidating all of those cartridges into one big ass cart, if possible. Stil a few days away from deciding on the best approach, but there are many alternatives. Other thing in the mix include finding the thread on the 1861 video chip replacement using PALs, which I think I will do while I'm at it. (I have a programmer for them and the JED files.) I am interested in this approach particularly for legacy stuff like this thing. That's the news. More as it happens.

any chance you'd shoot a good pix of the back side and post it and/or email it? i'd love to see if it matches the program card schematic i have. pretty cool. have you used it? does it work? this thread is getting so long it might take me a while to find your mention of it, but i do appreciate your mentioning that you have it.

Anyone know who bought this board from member Tempest? I'd love to get my hands on it briefly, and/or get a pix of the other side. It's some sort of Studio 2 programming board, nicely done.

so... i have one of these..... http://www.computinghistory.org.uk/det/6457/Fluke%209010A%20Micro-System%20Troubleshooter/ and later today, i'll have a pod for testing 1802-based systems. shiz about to get real. much easier than scope and hope technique, and i've been looking for an excuse. woot.

not quite yet. i have two consoles to troubleshoot and a few carts already for dumping and testing, so that's enough for the moment. the design I am working on will work for many if it works for two, and the only fly in the ointment is 2k games per Paul R, above. I am thinking about that now. Once it works in prototype, I'll play with the files I have that are available, and at some point, will deal with the additional undumped titles.

hi paul.... i have been meaning to drop you an email and introduce myself. you are an amazing repository of info on this thing and i am duly impressed! i'm in the schematic capture stage of this multicard thing and it is based on 1k pages. i thought that would be liberal and excessive for the smaller carts. what do you think? i suppose I could do a 2k page and bump the EPROM up to a 64K x 8. (I have a bunch of 32k x 8 chips and that's one consideration, but regardless, the concept it identical except for a few wires and some additional combinatorial logic.) Would 2k be enough? the scheme i have uses memory reads at 80xx to select pages. once selected, a short reset puts the unit into the game ROM and a long reset puts the unit back into the selection mode. if i understand the software properly, this shouldn't be difficult to do, but that's what i always say about software and i am always wrong. i am very tempted to buy an 1802 pod for my old fluke 9010 troubleshooter. might be handy for hardware wakeup but the last one i saw was $200 and i am a cheap bastrd. any suggestions greatly appreciated and this is the best time to get them in, as you know, before the concrete sets up.