bradd1978 Posted November 2, 2015 Share Posted November 2, 2015 I've had this board laying around for awhile but have had some issues with it. I've cleaned the cart connector, rebuilt the power switch, no AV mod just RF. The Coleco Bios screen comes up fine, difficulty selection screen runs fine, then the game starts and the top of the screen has garbage graphics. I've repaired many of these by replacing the VRam chips but usually the Bios screen is a mess, and referencing the service manual makes it easy to pin point the problem chips. This I have no clue where to start. Anyone experience this? Anyone know if its VRam or something else? Thanks :-) Quote Link to comment Share on other sites More sharing options...
SiLic0ne t0aD Posted November 2, 2015 Share Posted November 2, 2015 Still looks like RAM to me, perhaps just one bad chip.. I'd replace them all if you haven't done so already. Quote Link to comment Share on other sites More sharing options...
bradd1978 Posted November 2, 2015 Author Share Posted November 2, 2015 Still looks like RAM to me, perhaps just one bad chip.. I'd replace them all if you haven't done so already. That's what I'm leaning towards. I have a bunch of NOS chips so I'll probably just do that Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted November 2, 2015 Share Posted November 2, 2015 Yeah...I have one that was doing this. I attempted the +5 video ram mod (My second attempt at one) and once again went from garbage graphics to just a black screen when done. So... I do think the vram is the cause of any of this glitching, but just don't see to have any luck trying to fix it even with my Hakko 930 desoldering iron..ugh. Quote Link to comment Share on other sites More sharing options...
bradd1978 Posted November 3, 2015 Author Share Posted November 3, 2015 I have a Hakko 808 and I still have problems with those CV vram chips. Not a fun task for sure. Thanks for chiming in though. That sucks your +5 Volt mod didn't work. Did you double check solder joints and any possible lifted traces? Quote Link to comment Share on other sites More sharing options...
+nanochess Posted November 3, 2015 Share Posted November 3, 2015 It's pretty hard to remove the VRAM chips. You need to put new solder typically. It's easier to desolder, cut pins by the top, remove, desolder again. And all this trying not to damage the fragile pads by overheating. I had an easier time with the Z80 and RAM chips. Quote Link to comment Share on other sites More sharing options...
Nebulon Posted November 3, 2015 Share Posted November 3, 2015 Is it just me or is it brutally hard to melt the solder on these ColecoVision boards? I tried working on one and cooked it royally. Any tips from the pros? Has anyone had any success installing sockets for the chip locations to make future IC-swapping easier? Quote Link to comment Share on other sites More sharing options...
matthew180 Posted November 3, 2015 Share Posted November 3, 2015 (edited) The secret to soldering / desoldering, like welding, is having clean tools and work pieces; and no-clean liquid or tacky flux is your friend. Desoldering is *twice as hard* as soldering, so practice and patience are critical. If you are in a hurry or cut corners you are going to destroy your work piece, in this case you old computer. Get a box of Q-tips and 99.9% alcohol (no, the grocery store bought "isopropyl" is not good enough, it leave a residue.) Mouser has it (http://www.mouser.com/ProductDetail/MG-Chemicals/824-1L/) and Frys Electronics stocks the same product, as well as the flux. Get some medium-braid wick with flux. I also highly recommend ChipQuik (one SMD1 kit will last you a *long* time). Digikey sells it, and Frys also stocks it (I never lived near a Frys until the last year, it is really nice.) A hot-air bath will make you job much easier and you will have less of a chance of wrecking the PCB. I highly recommend you read all the while papers on the Zephyrtronics website (http://www.zeph.com/papers.html), especially the ones on the hot-air bath and low-temperature desoldering and rework. Very good information, and if you can afford their tools I recommend them. I made a hacked-up hot-air bath with my heat gun and really large joist hangers. It is not pretty, but it works and I can desolder / repair just about anything, even PCBs with large power and ground planes. You should have a decent temperature-controlled soldering iron. Also, get a brass-sponge instead of using water sponge. A water sponge will heat-shock your tip every time you wipe it. Keep your tip tinned with a blob of solder while it is sitting in the holder, better to burn solder than your tip. Wipe the tip regularly on the brass-sponge while working. Gently clean all the pads, top and bottom. Add some flux and reflow the old solder, maybe adding some new solder to the joint. Use solder with LEAD! Do not mix lead and lead-free. All the old systems use leaded solder. Get non-acid tin-lead solder with no-clean flux. You also only need about 645-degrees F for your iron. Don't run any hotter or you risk destroying the pads and components you are working on. Don't leave the tip on the parts any longer then you need to do the job, and never more than 5 to 8 seconds at any one time. Use wick to gently pull out as much solder as you can. This takes some time and resoldering the joints with new solder may be necessary to get all the old solder out. If you have a powered desoldering tool like the Haako, use it. I *just* got one not too long ago and it works great. You need to keep it clean though, which can be an adventure in of itself. I don't recommend the manual desolder pumps. I have one and have used it for a long time, but they tend to cause me to use more heat on the joint for longer than I would like so I tend not to use them. One place I do use the manual desolder pump is when I have a board upside-down over my hot-air bath and I have applied ChipQuik to a bunch of through-hole parts I am removing. In this case the joint is already liquid at the low air-bath temperature and I can just go around and suck the solder out of each hole nice and easily / cleanly. If you need to use ChipQuik on a through-hole IC, note that once you add the ChipQuik to the joint you will not be able to extract it easily with wick. It just does not work very well / at all. You really need hot-air with ChipQuik, but if cleans up easily with hot-air and an alcohol drenched Q-tip. You literally can roll the old solder into little balls and push it off the board. Be careful not to get ChipQuik on any joints you are not working on! You don't need a lot of ChipQuik, a little goes a very long way. Once you add ChipQuik to a joint, try to move the pin a little bit in its hole so the ChipQuik mixes with all the old solder. The joint will get nice and squeaky when it is all mixed and loose. When you are done and the part is out, depending on your method(s), you can resolder the empty holes and use wick to easily re-extract the solder. This totally cleans any old solder still in the hole and tins the pad and through-hole, and leaves the pad looking like it did the day the board was made (usually). Constantly clean and reclean the pads with alcohol while you are working, removing heated flux residue and old dirt. I wipe my iron tip on the brass-sponge almost after every joint when I'm desoldering. Work under good lighting and magnification. You can get a relatively cheap (or expensive, they are across the board) circular magnifier with a florescent or LED light that provides nice lighting for this kind of work. Good luck. Edit: By the way, you can use an F18A to fix your VRAM problems since it does not use the CV's DRAMs (they can be completely removed from the board or just left intact.) Edited November 3, 2015 by matthew180 2 Quote Link to comment Share on other sites More sharing options...
+nanochess Posted November 3, 2015 Share Posted November 3, 2015 Is it just me or is it brutally hard to melt the solder on these ColecoVision boards? I tried working on one and cooked it royally. Any tips from the pros? Has anyone had any success installing sockets for the chip locations to make future IC-swapping easier? Add new solder and everything goes easier! Quote Link to comment Share on other sites More sharing options...
Nebulon Posted November 3, 2015 Share Posted November 3, 2015 Holy Toledo! Thanks guys. I imagine you've already seen this (but just in case...): http://www.colecovisionzone.com/page/coleco%20industries/tech.html http://www.colecovisionzone.com/photos/coleco/colecovision%20tech2.pdf This ought to help people narrow down the chips to replace on the board. Quote Link to comment Share on other sites More sharing options...
SiLic0ne t0aD Posted November 3, 2015 Share Posted November 3, 2015 (edited) Check some Chip Quik, awesome stuff. Edited November 3, 2015 by SiLic0ne t0aD85 Quote Link to comment Share on other sites More sharing options...
NIAD Posted November 4, 2015 Share Posted November 4, 2015 Has anyone had any success installing sockets for the chip locations to make future IC-swapping easier? Yurkie has been adding sockets for numerous chips on the CV PCB for years and my main system that was modded up by him has sockets for the BIOS, Controller ICs and RAM chips. After all these years, I don't recall if he put in sockets for other chips like the VDP, sound chip, etc... I guess now I'll have to open her up to refresh my memory. 1 Quote Link to comment Share on other sites More sharing options...
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