Dennis Stith

I just skimmed through this article on impedence http://www.bluejeanscable.com/articles/impedance.htm and it looks like it has a bit of information to help me research this trouble and move along. I'm going to check the quality of my video cables and also check the resistance with a multimeter of the circuit. Apparantly by being around electronics for so long, somewhere along the way I learned of this magical (or not really so magical) value of 75 Ohms which this circuit has in it. Basically I have seen the term "75 ohm impedence" thrown around a lot, mostly in coax cables used to connect cable TV or VCRs to the tv set through the antenna input port. I'm thinking that either the cable I'm using isn't capable of carrying the 75 ohms across properly (which is pretty likely since I'm using a white RCA cable rather than a yellow one, though they do look the same), something in the circuit (two 150 ohm resistors in parallel for example, maybe something is wrong with the values of one or both of these in my circuit), or there's some signal noise on the composite cables I'm plugging in. That or there's something altogether wrong with the circuit or the way it amplifies the signal is not NTSC safe for the yellow color any more. If I get this circuit fixed, I'll come back and post my results here in case anyone else can benefit from my discovery in the future for their coleco set.

I just tried modifying this circuit to no avail so I put it back to the way it was. The issue still persists. Now I'm starting to wonder if it is the video chip causing this (well it doesn't if I use RF) or what it could be. I have 2 coleco sets. I guess I could add a circuit into the other one and see if the same thing happens.

Is there any alternative? $130 is a lot to pay just to acquire one 32kb rom file. I would buy the Atarimax SD but I just like the carts I currently have and use those, so I haven't really needed it. It doesn't seem like it would make common sense to spend that much at this point. Sorry, I'm still pretty busy ... I do have a bunch of emails to awnser You can have the Mario Bros REV.A rom when buying the Atarimax SD multicart Also included is Mr.Chin

I sent you an email but no response, pm no response. I've been looking all over the net and can't find the ROM.

Wow figure 3 reminds me of the arcade machine in SDF Macross Episode #24 where Max Jenius met Mirya for the first time. Pure 1980s nostalgia. And it makes sense because the arcade machine and the anime both came from Japan.

I did the power switch repair but since I put in LM318N now, it appears the problem is back probably because that LM318N takes power directly from this finnicky switch. But it should work. I posted a new thread about it anyway. The controllers don't have any issues unless there is something besides playing the games that I should be noticing with them. I replaced all 8kb DRAM with the +5V mod and the new ones work fine. I'm not sure what VDP is but I will definitely look into that. I just looked it up, TMS9928A Texas Instruments Video Display Processor. I don't see any sites listing a replacement part for it though mine appears to work. The RF module works fine but I haven't replaced its capacitor yet (yeah I know it doesn't need to be replaced but I have a brand new one so if I get around to it I might as well. it actually doesn't hurt anything, sans the "if it isn't broke don't fix it". You can always do maintenance on things if you know what you are doing and you won't break it. However if someone doesn't know how to work on the coleco without burning the pcb, breaking traces, or burning up solid state components then good luck )

I like the black short sleeve T shirt with the big logo and I like the mug. I'm interested in both.

After I repaired the power switch on this spare Coleco deck and replaced the 8kb of RAM with the +5V mod, the system would start up fine every time I powered it on. Now, with the LM318N taking +12V from the switch and a questionable capacitor between the LN318N circuit and GND, I have noticed that it doesn't always give me video when I power on the coleco now. So I basically somehow have reverted back to the original problem I had before replacing the RAM. I did take out the other circuit (which is detailed on Benheck's page) before putting in the LM318N circuitry so that can't be the issue. Maybe I need to do maintenance on the power switch again or there's something funny going on with that +12V. I mean it only gets +12V to the LN318N after the power switch has been turned on and that leads me to believe that possibly there's a capacitor on that circuit that is suppose to store 12 volts so that the circuit will operate before the power switch is turned on, otherwise that 12V might not be applied to the circuit soon enough for video to display. I'm just guessing on this. If anyone knows a work around to get the games to start better, please let me know. Thanks

Hi I just successfully built and installed the LM318N circuit in one of my Coleco sets. The problem I'm having is, I put in Smurfs Rescue in Gargamel's Castle and when I get to the first set of dark stages (purple sky with black overhang and floor), the graphics on the top of the screen stretch and glitch across the TV set. I'm wondering what I need to check in order to fix this. At first, I thought it might have been the RAM since I replaced all 8kb on the board with the +5V mod. I unplugged the composite video cable and plugged the RFU in and the graphics display properly. This means that it has to be the LM318N circuitry itself that is causing the issue. Any help would be appreciated. I am starting to wonder if maybe one of the capacitors has the improper value. The one on the schematic said to use >1uF for the +12V to GND but that is pretty vague for me. I installed a 10uF 25V capacitor there and it is much smaller looking than the one in the photo on the diagram. Also the ceramic capacitor I bought it smaller and of a different shape (it is a small shiney blue one) than the one on the photo I have in the PDF of this. Its value is 27uF and I wired it in properly. Any help would be appreciated. I'm just starting to think that maybe one of these two little capacitors might not be correct because it is probably for filtering noise.

I actually did finish this and there's a couple things that I can clarify from my previous post. I didn't have to desolder the pins from the RF shield but I did have to desolder the RF shield from the RFU completely in order to access the other side of it. I desoldered the RF out part and soldered the new one in. The traces on this board are susceptible to heat. They appear to try to separate when using a 25W Weller iron. This iron is overkill for this PCB and I am going to either switch to a 15W generic iron or purchase a 12W weller for future use on these. I would not recommend using a quality iron that is more than 15 watts. I thought a 25W iron would work out well but apparantly Weller makes a very very good 25W iron which creates quite a lot of heat So in short guys, don't go down to home depot buying a soldering iron and use it on your Coleco set. I was very careful and didn't mess anything up on mine but next time I'm going to be better prepared. The 25W iron seems to be better suited for more modern consoles that use lead free solder and require more heat to desolder things. Soldering onto modern consoles, on the other hand, is an entirely different story which would take us back to a lower heat iron anyway.

Alright so I finally got some time to take this back apart and take a look inside. I see a whole bunch of ceramic capacitors. I'm not sure how long these last so I'm going to leave them alone. They appear to be some sort of dry capacitor technology. The electrolytic capacitors inside the colecovision set consist of the following: one 50V 1.0uF, four 16V 10uF, and one 50V 10uF capacitor (on the RF board). All of these capacitors haven't blown but I assume due to how old this set is, they probably have completely dissepated by now and possibly are all open circuit anyway. It is late now so I'm not going to test the leads and see if they still work. I intend to replace all six of these capacitors with brand new ones. There is one more place that has capacitors though. I came across a video on youtube of a guy who dremel cut the power supply open and found one bad capacitor inside there. The power supply itself has some larger capacitors in it and unfortunately the only way to open it is to cut it open. I want to find a way to re-seal the power supply back together before I go inside of one. I own two coleco vision sets so one of them I'm going to fully go over and replace some parts including the DRAM and the other one I'm probably going to leave alone for the time being. Although I probably should replace the RF to composite modification in both units with the LM318N circuit board and see if I can find out what needs to be done to the audio circuit as I was reading last night that directly wiring from the texas instruments IC to the composite out for mono is a bad idea. I'll try to come back and post on here soon with part numbers from digikey so people know what to buy. Keep in mind that this maintenance I'm doing does not appear to be necessary presently since I haven't actually tested the capacitance of the parts that are still on this board. This is just for information only.

They don't just store power, they also filter it so it gives a clean signal. My first project was CCC (Carbon Copy Card) for Gameboy which is how I may have first come to understand filter caps. In its schematic, the author of the PCB stated where to put most of the capacitors and he gave a diagram to follow. The circuit board did not have holes for all of the capacitors in his diagram and so the end user is instructed to put them there only if he wants to because they are filter caps. All of the filter caps on that circuit were the ceramic type. I remember it has one large electrolytic capacitor on it (which I once mistakenly thought was bad even though it wasn't bulged). I replaced it once but later found out it was the power switch that was bad. Since the power switch was double pole, I just desoldered it, turned it around, and soldered it back in. Works. I'm uncertain if the ceramic type have electrolyte in them but it is doubtful so far. So I don't think all capacitors have "liquid" inside of them. But you have to understand that this liquid is soaked up in a paper/sponge like material so it isn't really ever going to leak out onto your PCB anyway. Also the electrolyte only dissepates in small quantities into the air and so everything is going to stay relatively dry unless maybe you toss the coleco into your bath tub and turn on the faucet Storage of small amounts of power can be done with solid components. There are "solid capacitors" now which most often are surface mount and still contain electrolyte. This electrolyte is mixed within a polymer, rather than being soaked in a sponge, and the whole thing basically is a solid prior to and after assembling. If you have a PC built within the past few years, take a look at the main board and you will see them on it rather than the usual electrolytic capacitors that are commonly seen on Pentium 4 and early Core2Duo motherboards. These solid capacitors take the place of electrolytic ones and also have a longer service life. I haven't attempted to replace an electrolytic capacitor in a circuit with a solid capacitor, but since electrolytic capacitors are usually so easy to replace I haven't really had a need to yet. Long ago, I found that if you calculate it, you have to keep a PC on 24 hours a day, all year for 3 years straight for the capacitors on the motherboard to go bad. There are some motherboards that continue to function longer and this probably means that the capacitors were mostly used to filter current and do not break the operation of the system when their life span has been exceeded. However, of course, there have been motherboards that failed prematurely, such as ASUS Pentium 4 boards primarily P4P800 series models, and that was due to the manufacturer choosing an inferior quality capacitor/manufacturer for it systems boards. I have a Pentium 4 P4P800 which is currently on its third P4P800 motherboard more than likely due to this. I'm not even sure why that computer still works today. Anyway it is possible that an engineer might tell you "they're needed" just to make things simple because they are used to a lot of people in their day to day life that don't want to listen to detail on why they do things a certain way (e.g. they won't understand anyway so let's give them a simple answer) However the ones I come across online always give me the proper explanation and in case of the project that I soldered together years ago, the CCC, it was clearly stated that they were "filter caps" (the ceramic ones anyway).

yeah that details electrolytic capacitors. I saw a few on the coleco board. but there are also ceramic capacitors which are light brown disc shaped solid state components. I'm not sure if those go bad but it looks like those are made from alternating layers of metal and ceramic only so probably nothing to worry about. there are so few electrolytic capacitors on this, it might be a good idea to replace them since the system is so old. they probably aren't doing anything any more anyway.

wow whoever is playing is terrible, look at the deaths lol. got a crystal out from the rock demon by dying even rofl. I see now though here, fire air then water crystals and the guy made 2 super crystals and went after the rock demon. apparantly that was too few. the tutorial I showed above said to make 8 and then go in there. I think you can do it on less but I just followed the instructions and it went well. In my save state, I have 3 dragon eggs and a pretty high score now. This game is fun but once you figure it out, you see that it is yet another repetative small game on the Coleco.

Awesome. I didn't realize there was a prototype of this game for Coleco. Cool stuff.