jdgabbard

Out of curiosity, does anyone know what the voltage at pin 2 of Q4 should be? According to the schematic HERE it should be 9v DC. However, from doing some reading, I am hearing that the cassette port specifies 6.5v DC for the motor. This doesn't seem right at all since it would end up being around 8.6v DC after passing through the transistor.

Here is a project for a digital (non-pc) joystick adapter: http://www.cithraidt.de/joyadapter/index.html

I seem to remember there being something me very obscure examples from way back in the late 90s. But I dont remember how common they were (I continued to use DB15 until the mid 2000s).

Does the MSX count? ?

I discovered this information and just had to share with the community. So I shot a video, and uploaded it last night. To be clear, its not a complete VIC-20. But should be useful to most collectors. This is also the basis for my post in the Commodore sub-forum about VIC-20 Video issues.

Yeah, its not the TV. However, I will say that I do get a little bit of a rolling interference (very light, but noticeable). At first I thought it might be an issue with the White and Dark trim pots, as Ive had a similar problem, and adjusting those worked. However, that has not been the case with this VIC. I am figuring either a resistor or a capacitor has gone out of spec, but without knowing a ton about the video circuitry of the VIC, or commodores in general, Im hesitant to poke around until I can study the schematic. Im hoping someone has seen this before and has a starting point to suggest.

Thanks for the reply. The TV gets used infrequently with various systems. A IBM 5160, TI-99/4A, SNES, NES, Genesis, a second VIC-20 (works fine with the TV), and various other computers. I have not tried it with a different TV. But that may be worth trying.

Hey guys, I recently came into possession of a VIC-20. Today I plugged it to test it, and was created with a short black screen during the memory test, then a composite image as below. Shortly afterwards (3-5 seconds later) the video did a slow creep into the second picture. Then another 3-5 seconds later it lost sync with the TV and the video was lost completely. Trying this again after about 10 minutes provided the same results: short black screen, composite video for about 5-7 seconds, then video distortion, then I powered off the machine. I wouldn't think it is the 6560, since I am getting video. But seems like it is loosing horizontal sync. But that is just my guess. Any gurus out there experience this problem before? I appreciate any pointers. Links to images of the video: http://retrodepot.net/wp-content/uploads/2018/07/img_5858.jpg http://retrodepot.net/wp-content/uploads/2018/07/img_5859.jpg

Yeah, sounds like poor connection on upper address lines. Maybe some cold joints? You might try reflowing with a soldering iron to see if that fixes the problem.

Yeah, I supposed I'll probably have to search through a lot of the older magazines. I seem to be just running in circles on Google...

Does any one have a copy of the Disk BASIC ROM listing, or even the Source, that includes comments? I've seen Disk BASIC Unraveled II as found here. But that is for the CoCo 3. I'd like to pick apart the commented code to see if some of it could be re-purposed for a pet project I think I'm going to start up. Commented code would help, as I'm not too familiar with 6809 assembly (most of my experience is with the z80 and it's mnemonics). I've searched for hourse, and I've had a hard time coming up with what I'm looking for. I downloaded F9DASM and disassembled the disk Basic v1.1 code with an offset of 0xC800, but the code isn't even close to that in the Unraveled book.

artrag, thanks for the link. I'll make another pot of coffee and go read. Like I said, I'm 'MSX Standard Retarded'. I've wanted to get into it for some time. And now that I've done as much z80 development as I have, I see no reason not to learn about this standard as well.

I also suggest the TL866 programmer. It tests pretty much everything where 74xx logic is concerned.

I really find this thread interesting as I finally decided to take the leap and buy my first MSX computer, I decided to go entry level with a Casio MX-10. But may step up from there. I see a lot of talk about the SD Cart with 512k of onboard ram. Seems to be beneficial to any MSX. But the website doesn't seem to elaborate on any of the technical specs (I'm assuming a lot of that is so that they're not ripped off by someone wanting to sell clones). But being basically dumb to the MSX standard, I'd like to find more information on exactly what features this offers. Anyone have any place they can point to? From the perspective of someone who works with electronics quite a bit, I am going to say it really just depends on the particular design. Internally, it is going to go through a transformer which is going to lower the voltage from 110v or 100v down probably something in the range of 24v A/C (if 100v) or 26v-ish A/C (if 110v). These transformers step down by a ratio, and have their own limitations. But assuming they planned for the potential for +12v and -12v DC, at this point it would (most likely) go through a bridge rectifier which would convert to DC voltages. Either +24v, or +12v and -12v. From those voltages it would be regulated down to the required voltages. Assuming +5v (virtually all components work at 5v, but later on would go to 3.3/3.6 and now days down to 1.6v...), there would be at least a LM7805 (most common in that era). So the question really just depends. In most cases, I would say that the biggest problem would come from the voltage regulators which would have to dissipate more heat from the increased voltage. Most of the time this isn't going to be a problem. But over time heat helps to break older components. So my concern would be what was the initial voltage fed to those regulators. Ie, are we feeding an LM7805 with 12v at the preferred 100v? If so that 13v isn't going to make a huge difference. But if we're feeding it 24v at 100v, then the 26-27v at 110v A/C may put it way over spec and cause some pretty serious heat problems resulting in magic smoke escaping.... It really comes down to opening up a particular design and seeing how it is made. Probing around, and determining for yourself what the accepted tolerances are. If you don't feel comfortable with that, its best to buy some type of step down / step up rig that can convert to the specific voltage / hertz you need.

Centurion, I didnt realize that was another members blog. I read over that a while back. Good read. I plan on 3D printing my own case. Though Im not sure if I will use the original keyboard, one of the new tactile keyboards, or just stick with my idea of using a custom mechanical keyboard. Ive already got the PCB layed out....leaning that way.... As for the boards I ordered, I just got notification this morning that the boards are done and being shipped. I should have them in a few days. Here is what the board house sent by email.

Thats correct, its just the PCB. But the I also ordered the two most expensive components from overseas ( The ADC was $15, and the voltage regulator was $5 from US sources) which substantially lowered the cost of the BOM. I will have extras if you are interested. But youre still looking at about $60-80 in BOM cost. But youll have a working NTSC PCB. But if youve never built a kit computer, this might not be for you.

You can occassionally find new old stock of Beige towers. I found a listing on ebay back about 2 years ago that was selling Beige Towers that were between the P-II and P-III eras in styling. I ended up buying two of them. One is housing a Pentium II system with a Voodoo II card. The other is sitting in a box waiting for the day that a suitable donor comes along. I also aquired 3 decent Pentium III era towers (matching) a while back from a buddy of mine who was cleaning out an old house. However, one has some damage done to the metal, it and another have paint damage, and the 3rd is in awesome shape. I currently have a P-III system in the nicest one, and the two other sitting in a closet waiting to get dealt with. Then there is the IBM Aptiva 350 that I acquired along with a IMB 5160 several years ago. The Motherboard is dead as best as I can tell (no signs of life, although I have not probed around on it). It was a very interesting case that I really like. But only with that it would have fit a standard AT/ATX style MB, rather than the awkward dual-riser style that it sports. I currently have a P-I Industrial SBC in it, just taking up space in the top of a closet. I'd really like to find some decent priced (and in decent shape) AT "Mini" Towers in with the Frequency LEDs on the front. Preferably with toggle style power switches rather than push button. But that is just a pipe dream, as I do not tend to see any for less than $100 even for ones that are in horrible shape. And sadly, I think the scrappers have acquired all of the ones in my geographic area. But I'm way off topic now. You're right. Beige / White / Cream was a classy color for computers. They really should bring it back.

I saw this posted earlier today elsewhere. It's a pretty cool idea. But they lost me once they got the price tag that they put on it. It's too expensive for a novelty. If I want on that bad, I'd just try to 3d print it rather than spend a couple of hundred dollars on a computer case.

VicViper, it's interesting that you bring this up. I just ordered a small batch of Harlequin 48k boards about a week ago. I really only need one, and will likely offer the others on my website. But there are also several ebay sellers out there for the 48k and the 128k variants. If you're not familiar with the Harlequin, you might check it out. It has NTSC compatibility. It can be a little expensive to build one, since they have quite a large BOM. But are a good option for us in the US who need an NTSC option.

I was actually looking at the LM1881N and the LM1981 ICs this weekend. They are video separator circuits that can strip the sync (1881 = vertical, 1981 = vertical and horizontal) signals out of a composite video source. Then you would just have to translate this to a 9v logic level, as well as inverting (I believe). That means you should be able to tie it though a transistor pair (for amplifying) to a 74LS06 (open collector) to generate the 9v sync signal.

Don't feel bad. I know nothing about analog signaling either. But how you just described it made a lot more sense. My understanding from reading the the information I had is that you still need a way to slow down the signaling to match the VDP's. However, what you're saying is that the 9918A handles that itself. You just have to tell it when to do it, i.e.: provide the 9v sync signal. And if it truly is that simple, it should be just a matter of inverting the horizontal sync and amplifying the signal to a 9v level.

Tursi, thanks for the response. You're always Johnny on the spot with your experience. So to confirm what your saying, when the TMS9918 is fed a composite signal without decoding the Sync (and timing it with the VDP's sync) the video in seems to display just fine when the external video is the only thing on the screen. When an overlay is attempted they get all out of whack. And when the TMS is just doing it's normal everyday thing there seems to be crosstalk between the two. Would that sum it up? In your experience, do you believe it would possible without a lot of hardware? It seems like separating the sync from the composite signal is doable. However, timing it to the VDP wouldn't be so straight forward. Obviously it does work, as you have played with it yourself. However, I'm curious if it could be made reliable without having to create a whole new daughter board full of circuitry. It seems like you could use an open-collector not-gate (74LS06) to generate a 9v sync signal from the composite video. Since the sync signal is below 0v. However, then you'd have to figure out how to amplify the lumanince above the required voltage to switch the 74LS06 back on. And then you still need to create the timing....

While messing around with my 99/4A, I decided it might be fun to rig up a circuit to play with external video. From my understanding of the 9918A, the EXTVDP pin is the pin that is responsible for video input. As I understand it, this was used on some computers to do video text overlays. However, I cannot find any documentation of this. The 9918A manual suggests that it is used solely for the purpose of cascading VDPs, utilizing RESET as a "Sync". To my mind, this was in reality a poor man's SYNC, as you're only resetting both controllers to put them on the "same page" so to speak. And would make sense, since the circuits I have seen show that both the VDPs use the same crystal oscillator to keep "in-time". But that is just my impression. Who knows a thing or two about the the EXTVDP pin, and can speak intelligently about video input circuits and how they interface to the VDP? Is it as simply as supplying the EXTVDP pin with a composite signal? Or is there something more that is required? The BYTE article on the 9918A adapter for the Apple I ("High Resolution Sprite-Oriented Color Graphics" - Steve Ciarcia) has a schematic that suggests that it truly is as simple as inputing a composite signal. However, the text of the article contains the following: To me that suggest that there needs to be some type of decoding logic. But for the life of me, I cannot figure out how this would work. Even if you used the composite signal to creat a SYNC signal, there would still be no way of synchronizing with the VDP's clock. But it seems as though it should be possible, as I seem to remember hearing somewhere that MSX computers were popular with TV stations for text overlay. Does anyone have any information on this?

Archive.org is one of the coolest websites I've ever found. Literally, everything you can think of is on there somewhere..

If you're interested in this project, I have been updating my YouTube channel as well as my website as I progress. At this point I've already ported TinyBASIC over to the system, integrated it into my monitor, and expanded it with several useful BASIC commands. Here is my latest video, and my website is in my signature line. I am also planning on adding mass storage, but I need to get some protoboards in the mail before I can start.