ceratophyllum

Thanks, Rolo. Now I have one more thing to try before pulling out the soldering iron.

I bought a few cocos on eBay listed "for parts" and discovered they had no Extended Basic ROMs and that 24-pin eproms are not common. I found these neat 28 to 24 pin EPROM adapters for the C64 over at Retro Innovations. I didn't want to say anything until I had tested myself but all you have to do is flash an Extended Basic 8192KB ROM from MESS onto (for example) a 28-pin 2764, plug it in and you've got Extended Basic. No hex editing, soldering, or jumper wires...just flash and plug-n-play! I used the TL886CS USB eprommer with minipro and a 8KB ST M2764A-2F1.

I just got around to checking and I got 750 ohms across 1 and 16 for G pressed down. I tried F and O and got around 300 ohms. I think the problem is on the trace16 of the flat, cable sticking out because the resistance increases a great deal in just a few cm closer to the end. If I move the probe up the trace toward the keyboard (keeping the other end fixed, of course), the resistance is more like 360 ohms. I have seen this before with my other coco2 keyboard: oxidation or something eats these traces up. That one had it so bad you could see the break. I just tried painting over the high resistance section of trace with a CAIG Circuit Writer pen and went from I,O, J,K, N, M not working to all but O working. The ink takes a very long time to fully dry and the resistance of the wet ink is high. Maybe I'll wait another 24 hours before I check again.

I have F18A installed but I don't have Geneve 9640. (I've never seen one of those before. The Kmarts around here never carried them, LOL.) Can the menu system work on a regular TI, Extended Basic, PEB w/32KB (or nanoPEB). If it can, where can I find it? What's BOOT? I use CFMGR to browse the volume list and insert/remove volumes into DSK1-3. Funnelweb "DiskReview" to browse and launch the disk contents. CFMGR is not so good at loading EA5 games, often there is no text or a lot of graphics corruption. Launching from Disk review works a bit better. Can you point me to one of these disk images? I often get this when I start up with one of them in DSK1. I think I might have messed it up by shuffling things around or copying to CF7 400KB image. The games load in F'web diskreview, just LOAD is broken. GAMESDSK3.dsk

The keys press down on a sandwich of clear plastic sheets with some kind of conductive paint traces. -------top circuit sheet -------insulator sheet with holes under keys -------bottom circuit sheet The sheets are bound together in the corners so that they stay aligned. I gave the area around G a good spray of contact cleaner but the key is still not working. There is nothing special to the naked eye about that particular key's movement or the point it presses down on. Maybe I'll take out the 18 (no kidding!) tiny screws again and have a look with the ohmmeter. Not sure how I would fix a flakey trace...Circuit Pen, I guess.

With the 8 new 4164 chips, I get 24871. I have an Extended Color BASIC ROM in this system, no cartridges or other funny stuff inserted. According to the the instructions above, this is the right amount: Too bad the author doesn't say which issue and page of RAINBOW has the memory test program. I'll just play some games and see what happens.

The games seemed fine at first but little things were off like some letters were corrupted so I went ahead and soldered that jumper W1 (Figure 1 in the PDF below) and replaced them with NEC 4164 chips from eBay and now it is fully working except for the G key. The old chips have numbers: 8040517 8329 and Motorola "M" and Tandy Computers "TC" symbols. Coco2 memory upgrade instructions The May 1984 Rainbow (page 49) referenced above is also a very nice help for the confusing and hazardous (There are too many types of coco1 boards!) coco1 RAM upgrade. I just ordered some more 4614 RAM to upgrade my 16KB 26-3004A "NC Board" coco1.

I have a lot of game cartridges on disk. Most of them are supposed to be EA 5 loaded and I have been customizing FunnelWeb to use them on NanoPEB. I've tried a few games and they seem to load ok, except for DigDug which crashes if you get killed or complete the first level. Anyway, I was just wondering if there is something better/simpler than the F'Web CONFIGURE menu. (I think I've deleted most of the bits that are not needed just to have a menu and the capability to load EA5 PROGRAMs.) I know there are already lots of cool multicarts full of games; making things easier to find on my nanoPEB is just for fun. atari.dsk

Is there a way I can remap a key with a poke in immediate mode? I have extended color basic on a coco2 and my G key will not work. Would be nice to make some other key do ASC(71).

I sorta fixed one of these with "Wire Glue" and a short wire jumping across the bad section of ribbon cable. I say sorta b/c this water soluble glue is not very strong and I am hesitant to cover it up with epoxy because there there's no easy way to get that stuff off when something cracks again. As for the other with the bad "G" key, it looks like I am going to be spending some time poking around the inlay with an ohm meter.

I replaced the socketed 6821 with a 6822. The coco2 still doesn't work and the junk on the screen looks the same. I also tried another CPU. The screen got a little less fuzzy, but the pattern of vertical bars remained the same. I'm not in a huge hurry to unsolder the other 6822 and I'm still waiting on the socket to come in the mail. It was nice when one could just go to Radio Shack and get parts same day..... The SAM is also in a socket, but I don't know where to get a replacement except from another coco. Then there's the 8 RAM chips soldered to the board.

No idea what is the deal with the G key--cleaning did not work. The older keyboard has (most of the second row of the keyboard array (m n i j k l ) not working ) a broken trace in the ribbon cable. Maybe some conducting glue might fix it?

I tried a LOADMing a few games(Space Ambush, Cuthbert in Space) over drivewire and it looks like they work ok. Now if I could just fix the damn keyboard...Took all those tiny screws out, dusted it off a bit, and voila the G key still doesn't work. That plastic membrane sandwich looks like a really great home for mold and tiny bugs. Maybe I'll get a PS/2 adapter from cloud9....

I wrote down the wrong number above, it should be 6439. PCLEAR 1 PRINT MEM gives 11047 I'm also autoloading HDB-DOS 1.4 DW3 from a cartridge. So this is a 16KB system?

I recently got another almost-working coco2 and I think it has 16K ram. The RAM might be bad, because PRINT MEM gives a funny, small number: 6913. Everything on this coco2 is socketed so it should be an easy upgrade, if what I read here is correct. I just solder across a jumper and put in 8 4164s. But what is 4164? Is this the same part?

I have a couple of coco2 keyboards and one has a G key that doesn't work and the other with a bunch of dead keys. I tried cleaning the connector contacts of both, but it did not help. One keyboard has a bunch of small screws on the back, the other I'm not sure how to open because there aren't any screws. The screwless one is from a 16K coco2 and looks slightly different from newer keyboard.

You know, I would like to know more about EDTASM+, too. With my other retro systems (C64 and TI99/4A) I ended up setting up MESS for testing and using a cross-assembler on my PC. Too much eye strain on an old TV and 40 column text editors are mostly no fun. (I also keep typing extra colons because I'm so used to vim. Doh!) Maybe if I had one of those TV to VGA converter boxes for the coco2 it wouldn't give me a headache.....

Haven't given up...Just ordered a few MC6822P PIA from el cheapo dodgy Chinese part supplier. Should arrive in a fortnight if I'm lucky. Possibly PIA-related: Is a coco2 supposed to click the cassette relay when you turn it on? This never happened for me, even when mine was working.

Got my Chinese EPROM eraser today. It took 15 to 30 mins. (First time I tried 15mins and it was all still there when I read the chip back with minipro. 30 minutes wiped it.) I don't really understand why the data is arranged in this funny way, but whatever: putting the Turbo Forth 1.2 "turboforth.eprom" file in the first and last 16KB, with 32KB of FF in between works in my real TI. ./minipro -p "NM27C512 @DIP28" -w forth12_40and80col_64K.bin Found Minipro TL866CS v3.63.2 Chip ID OK: 0x8f85 Writing Code... OK Reading Code... OK Verification OK My first working EPROM. In case anybody else has this particular board+EPROM and wants to upgrade, attached is the turboforth 1.2 image, padded for 64K v03c Guidry board with NM27C512 EPROM. I was just using my old BLOCKS disk. I didn't notice there was a new one. I'll wait until the official one comes out; I'm still trying to get my head around Forth...it is so strange. forth12_40and80col_64K.bin

I get 5.08 V at the side of R2 closest to SALT (IC1). Tried to look for AC ripple with my crap scope. If it's there, it's not much...shows a pretty flat 5.08V. At pin 15 of SALT, I get -13.05 volts. According to page 57 of the service manual(attached below), these are indications the power supply is OK. 6822P is socketed, 6821P is soldered to the board. I guess I'll look for another 6822P first.... How hot is Q1 supposed to get? I see it has a heat sink on it, but I can feel it through the case even with the coco switched off. I noticed this right after I got the system, while it was still working. Could this be a sign of trouble? The manual says check that the amplitude of the ripple at the cathodes of D3,4 is less than 1V, and check at anodes of D1,2 to see if its less than 0.4V. (Compare to figure 5-1, included below with a snap of my scope screen. I can't get an image AC-coupled, so this is the best I can do. D3,4 looks OK, but the ripple at anodes of D1,2 might be a little big? Damn this scope.)

Me too. It was just barely touching: the pin was bent like this ">." I mean the bottom part was going back into the socket. I've got the service manual and I'm going to check the power supply when I have some time at home tomorrow. The computer stopped working the first time I tested it with stuff attached: a "flash pak" cart (containing HDB-DOS) in the side and a Drivewire cable connected. Maybe the power supply was really weak and about to fail; straw that broke camel's back. There's a troubleshooting flowchart, but I'm not sure I want to go much deeper than checking that it's putting out close to 5V. Maybe just try another power supply if it's not. I don't have a good scope, one of those cheap slow scope-meter combos with a bad, impossible-to-see LCDs. Unusable without a headlamp. Is there anything funky about the original or would any old regulated 5V DC power supply like the one from a Play Station Portable (good for 2 amps) do it?

No change after reseating the CPU, MC6847 and the two smaller ICs U12 and U13. Wish I had a spare CPU.... Would this work? Would be an upgrade if it did....

The previous owner definitely did some work: two of the screws were missing when I took it apart. It looks MC6847 is not seated properly because one of the pins is sticking out. It looks like it is just barely making contact with the socket. It is near the top resistor in the picture. Ugh. It is hard to reach that chip with the RF modulator so close, the keyboard connector (it seems to have become one with the ribbon--I dare not pull too hard), and the DIN ports surrounding it. Very little change typing. Entering SOUND 60,20 does not make sound.

I think I remember having a Tandy DMP-1XX printer and reading about ROM upgrades. I used this printer on a TI99/4A connecting it with an Axiom ParallAX. I think I also used it later with a Tandy 1000. But yeah, the print wasn't that great looking even by dot matrix standards. It was better than no printer, I guess.

-ing. (I can't edit a title once it is posted? That makes it hard to mark a post as SOLVED. Oh well.) Anyway.... I was playing MegaBug yesterday evening and the computer froze. Everything just stopped moving on the screen. So I turned it off, removed cartridge and cables (drivewire + joystick) and when I turned it back on BASIC would not appear. The first time I turned it on there was a solid yellow screen. I turned it on and off a few times and I mostly get this pattern of vertical bars that shifts very slightly if I press keys. Does anyone know what has failed? Looking in the top vent, it looks like most of the big chips are in sockets. Is there any point in even troubleshooting this, since I doubt I will be able to get replacements? I don't find CPU, SAM, PIA, etc. part numbers MCXXXX outside of retro computer sites when I search..... Here's what it looks like: