cwilkson

Yeah, that was the excuse. If it ain't broke don't fix it! Weather wasn't so bad...things that were exposed were typically in weatherproof enclosures. And sometimes potted in rubber or even epoxy. Water wasn't getting into those. But some stuff like in the signal shacks by crossings was just normal metal cabinet enclosures. Which is fine. Until the roof leaks. Or when it floods.

Having worked in the railroad industry for a short time, I can tell you that NOTHING changes quickly. Around 2010 when I was in the industry, they were still using relay logic systems in parts of the freight world infrastructure. Yes. THOSE relays. The electromechanical clicky ones. Used to perform control logic. They had considered using vacuum tubes but they were not reliable enough. And those new transistor things were still too new and unknown....after 60 years in mass production! It was insane! To be fair other parts of the system were fully modern with microprocessors, cell radios, etc. But not all of them. Fun fact: Train detection track circuits use the rails as wires and the signal is something like a 1 kHz sinewave....at 10 amps peak! A train is detected in a section of track when the bogeys (wheels + axles) create short circuit between the 2 rails, passing the signal from one rail to the other. The train itself is the switch.

I have a DMP132? I think it's a 132. It was a GREAT printer! It had both parallel and serial ports. I used it with my Coco 2 in high school and briefly in college. But I haven't used it for 30 years. I need to just sell it. I remember having a program to do graphics screen dumps. It took forever to dump a PMODE 4 image. But it was really cool. I wrote my own basic program that was much faster. IIRC it could dump the screen to paper in about 1 minute. I always wanted to go back and see if ASM could speed it up. But I think the print head was the limitation. Or maybe it was the baud rate. I think it was limited to 1200 or 2400 baud over serial.

That thing is cool. I was looking for an EAI machine for a long time but gave up finally. Would love to have one.

2nd data point. I just purchased a Harmony Encore with this issue. (Shipped 9/6/23, received 9/11/23) I downloaded the latest software (HarmonyCart-1.3-win32.exe) and I beat my head against this issue for a couple of days before I found this thread. I can confirm the updated 2k4k.arm file (424 bytes) fixed the issue.

Ok. I know you've been to hell and back on this thing. But I didn't see where you had confirmed measuring a buffered clock (PHI_x). It's mainly a check box/sanity check kind off thing and I also wanted to document for posterity. I'm glad you did that that check. One other thing I thought of if you ever come back to it. Maybe the board is dirty? Not standard dirt, but something special. Like carbon scoring or chemical contamination. (even soda could do it). You mentioned the original TIA was damaged. Or at least is was suspect. If there was an "event" it could have left tiny conductive paths that are stealing energy from the oscillator.

One sanity note. "Never" measure a crystal oscillator's output directly. Others have alluded to potential loading effects. In many crystal circuits, adding a scope probe's capacitance in the wrong spot can completely kill the oscillations. Best case, it can slow the circuit down a bit. You should measure the frequency of PHI_0 on TIA-pin4 instead. The ideal frequency here is (105/88)*1MHz. But you should divide your crystal's marked frequency by 3 to get your "correct" value for the CPU clock. To get the best resolution from most scopes, put a single period of your waveform on the screen. And turn on averaging if your scope supports it. Use a big number for the averaging. And measure both frequency and period. Period may be more accurate on your scope. I really don't know...I've never used Siglent gear. Compare your PHI_0 frequency from the problem machine with another one instead of the using OSC frequency.

Got it. That's very interesting. I know that the '723 was pretty popular. It's quite a versatile IC. It can support linear voltage, linear current regulation, and even temperature regulation. And I'm pretty sure I used it to control a switcher back in the 90's, based on a Radio Shack app note. But it seems kind of wasteful in a simple linear regulator vs. a 3-pin regulator. BTW, with a dropout voltage of 3000mV I would never call the '723 a Low Drop Out (LDO) regulator. No matter what TI marketing wants you to believe.

Thanks for the catalog reference! The 26-210 looks like it might work with an MPI. But maybe not. I was looking for one a few years ago but didn't even know what to call it. Or that is was designed for the Tandy 1000-EX. Now I have a few new search terms to work with! Has anyone here actually ever *seen* a 26-210? LOL

Weird sockets on that supply board. What ICs are used? LM723? Or some type of quad opamp?

What is the revision status of the NTSC CleanComp? (the website says v1.0?) I'd like to buy one to compare/review, but it clearly has some pretty serious issues remaining. If the next revision with fixes for these issues is almost ready, then I'll wait. Otherwise I'll get the current revision and live with (or fix) any problems that exist.

What? Really? Still? I thought they supported horizontal video for a year or two. I admit I'm not into TikTok, but I could swear they support it. Damn.

Why are you using a SMPS? I don't see a need and it will only cause you extra grief as you've already pointed out. But maybe there's something special in your circuit that requires a weird voltage? For transistors...are you using BJT or FETs? What type? BJTs are probably faster at the cheap end, but storage delay will kill you if you don't compensate for it correctly.

Real quick cinematography advice. Turn your phone 90 degrees!!! And tell all your friends to do it too! To take advantage of basic human vision wetware. And every computer monitor everywhere. You'll have a bigger viewable image without wasted pixels at the top and bottom and you won't need to pan and scan. You can then use a cheap tripod to avoid shaky cam effects. Even propping the phone against a stack of books will work. I said cheap!

Nice update. There is quite a bit of noise and edge fuzz in the screen captures. I would like to see photos vs. captures to see how much of that is caused by sampling. Your composite waveforms look surprisingly nice. Good band filtering where there's color. Some over/undershoot on the luma stairsteps but it's minimal. Good job! It's great that you're using a scope to actually *see* what's happening vs. guessing and hacking. Makes it *much* easier to improve things. Keep working on the timing between signals. Those spikes are pretty severe and might be visible on a good monitor. Especially if they happen at a bad time. Need to hammer them flat! Be sure to check the waveforms with color active at both edges of the blank pulse. That's one of those bad times. Looking forward to the deep dive for S-video.

Moire pattern on screen is interesting. Does it change if you move your head? Which PVM is that? Overall it looks nice! If you don't see the bars in composite it probably has the comb filter enabled. Esecially with how bad they are on the other display. If that was S-video, then the luma signal is filthy with chroma contamination. BTW, you can see a red shift on the left side of the tree trunks and a green shift on the right side in Pitfall above. It could be caused by a phase shift between the luma and chroma components on the new video board. But it could also be due to the basic nature of NTSC. You can't escape those vertical edge color artifacts entirely without specific filtering inside the monitor. It's in the design of the NTSC chroma signal. And better monitors will be able to show it better. Unfortunately. In general when trying to retro fit these upgrades to old consoles, sometimes better is less desirable. It's funny. Check Pitfall II to see how sharp the color changes are. Pitfall II is more pronounced due to the particular color hues chosen for trees vs. background. IIRC, Pitfall II has a right side shadow that is unavoidable. And check both composite and s-video. Composite comes with some special problems, but it also hides a mulitude of sins. S-video will tell you how well the Luma and Chroma signals are matched in time and amplitude.

Those bars are from a high-amplitude chroma signal coupling into the luma signal. It should not happen with S-video unless you use unbuffered signals for mixing a composite signal. It can also happen with many "magic bullet" video mixer ICs. Bad layout on the board and poor quality cables will compound the problem. Unfortunately the bars *will* happen with composite to some extent...by definition of composite. And ironically, it will look worse on better monitors with more lines of horizontal resolution. They have a better ability to produce sharp vertical edges and they are able to reproduce finer gradations of luminosity too. It's a bad combination. That's why I tested all of my stuff with the "HR" (High Resolution) version of the Sony PVM monitor. It was absolutely beautiful and terrible at the same time! LOL Possible after the fact work around for this thing: If your monitor has a NTSC comb filter available MAKE SURE IT'S TURNED ON!

That's not correct. The 2600 chipset is an NMOS system. All 3 chips are specified for VCC = 5.0V +/-5% (= 4.75~5.25 V). With the exception of the CD4050 (if that exists on your motherboard) which is CMOS and will work correctly down to 3V. TTL also requires 5V +/- 5%. And many cartridges use TTL chips in them. The above is good advice. 4.06 V is unacceptable. You have a few likely causes: A bad wallwart (transformer). A bad filter capacitor. A bad regulator. A short on the 5V line. This is less likely. How you fix it depends on what gear you have available. Try a different known good transformer. It should be 9VDC. And rated 500 mA to 1 amp. If that fixes the problem your wall wart is bad. Get a new transformer. If that doesn't fix it.... Use a bench supply set to 9 VDC. 1 amp is more than enough. You can clip the supply directly onto the filter capacitor leads. If that fixes it your filter capacitor is likely bad. Replace it. If you don't have a bench supply available try the following. Measure the 7805's output with your meter set on AC volts. The output should be very close to 0 VAC. If your meter has a "minimum voltage" function, that can help. Use it and verify that the input voltage never goes below 8V. If you have an oscilloscope that's even better. It can immediately tell you which component is bad. Let us know! If you have a spare 2200uF capacitor you can connect it directly to the existing one's leads as a test. If the 7800's output voltage improves a lot then the original capacitor is likely bad. If you have rock solid input voltage that never dips below 7.5-8V then replace the regulator with a new one from a reputable source. Regulators are cheap and easy to buy from legit distributors so don't risk counterfeits (not ebay or Alibaba or what ever). So are filter caps. Always try Digikey or Mouser to start. Or you can go to Arcade Parts and Repair. Peter sells good stuff. Here are some direct links: https://www.arcadepartsandrepair.com/store/pinball-kits-parts/pinball-parts/7805-voltage-regulator-5v/ https://www.arcadepartsandrepair.com/store/components/capacitors/axial-capacitors/2200uf-25v-axial-capacitor-105c/ EDIT: Fixed a lot of typos.

Almost certainly composite and audio. That up close photo only shows the ground wires. You need to follow the cables under the shield.

I sent you a PM. I'm not sure what you mean with the chroma shift and inductor. What's the exact issue you're trying to solve there? And how? Maybe pictures are the best way to explain: Show the problem on the existing waveform. Show how you'd like to modify the waveform. Show your proposed schematic fix.

Which mod are you using? Schematic available?

I really like your 2 write ups. So many of these 2600 mods just kind of hack around and shove stuff together until they get something that "works". But it looks like you put real effort into studying the stock circuitry and finding weaknesses and defects and possible solutions. Great job! There are still a couple of things for you to find once you get this pass tested but most of the things you've already tried to address. Where are you located? Are you trying to make a PAL mod? (I noticed your reference to COL phase shifting on alternate lines.) Also....Pditfall is supposed to be green not blue! The PAL version especially interests me. Seems like there are a couple of things that would be easier to fix if you had alternating chroma phase available. I dabbled, but never really dived into it. When you get it done I would be really interested to see how it stacks up against mine. And at which level. I made several back in the day, ranging from "pitiful hack" to Prosumer to VGA output. I also had an HDMI version mostly worked out but I became disillusioned with the hobby and walked away. EDIT: PS. Be careful reducing the pull up resistors. The output transistors were designed for about 1.5 mA of sink capability. You can create local hotspots on the die! Best case...nothing happens. Realistic case #1...The pulldowns won't go all the way "low". You may have sync issues, or image dependent luma levels. And if you use CMOS buffers they'll run hotter than they should as their inputs approach VCC/2. Realistic case #2...(less likely, but possible)...Those local hot spots may affect your COL delay chain => unwanted color shift that is image dependent. Bad case...(unlikely, but still! It's bad!)....The hots spots are bad enough to cause your semiconductor junctions to blur and the transistors will stop working over time. The TIA is dead from this. Just be careful.

Oh yeah. And their site wouldn't today. probably a work/vpn thing. I got it loaded now. And ordered. Thank you!!

I want to purchase a Coco SDC. But after searching online, nobody seems to sell them at the moment. Any ideas where to buy? Zippster store = sold out Boyson Tech = closed until January. I really want one of these ASAP. I prefer a new unit, with or without case. But would also consider a used one if anyone is selling.....

I've been wanting to get my Coco 3 system running again for 20 years or more. It's finally set up and running! And now that I have the floppy drives working again and I can read my old disks it's time to move away from that storage format. I currently have an FD-501 controller plugged into a Multipak Interface and it controls 2 physical floppy drives. In the future I want to abandon the FD-501 and drives altogether. I need to do the following: Copy files and complete disk images the physical floppies to an alternate storage medium that's accessible by the Coco for long term archival purposes. Use that alternate medium as a 100% replacement for the physical drives. For compatibility it needs to appear identical to 2 or more real drives from the Coco's point of view. Move files and disk images between my Coco and my Windows PC. The PC could act as a virtual storage for the Coco or as an internet gateway. Or both. I don't care as long as I can upload/download between the internet<->PC and transfer between PC<->Coco. Run under both DECB and some flavor of OS-9 (probably Nitros-9 with a 6309). Multipak Interface compatible. Over the years I've seen many disk replacements come and go. But I don't know what is considered the latest and greatest setup. This is where I need help. What are other people doing? What do folks here recommend? I've seen references to Coco SDC for drive replacement on the Coco side. Can I transfer files between the Coco and the PC using "sneaker net"? I.e. using the SD card to transfer files back and forth? I've also seen references to Drivewire for transferring files PC<->Coco. And for using setting up the PC as a live file server for the Coco. Is one setup better than the other? Should I use both together? What is the optimal set up these days?