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If the game works where you can hear sound and such then you have removed more than half the trouble shooting. If its working the cpu, clock, sram etc is all good. That leaves VDP, video ram, RF board. A composite cable into your tv and pin 36 of the vdp should show you a B&W picture. If it is garbled than it could be bad video ram. The atari module will eliminate the RF portion.

So, today I embarked on repairing my expansion module. Let me share a few tips/things I've discovered about these modules. I have 2, one works and one doesnt. I also have an Atari 2600 for testing too. So first off, when I power it on I get a blank screen - or if on and off a few times a few lines but no real picture. At first I thought VDP/TIA chip. I replaced the Coleco TIA with the Atari one. Same thing. Put the Coleco chip into the Atari and no picture. HOWEVER if I put the "Bad" units TIA into the good unit it works. (This tells me the Atari TIA and Coleco TIA are incompatible) So far I have replaced the RIOT chip, and have the same issue. This leaves the processor and 2 transistors. I'll try the processor first, but I am leaning towards one of the transistors, since most likely (Q1) is probably used in making the composite signal. (Just a guess) I havent traced it. I've seen little point since the Atari TIA is different than the pinout between the two would be in question. I'll update if I get it fixed or find anything since there is no info out there on these things.

Tursi, Sorry, your right, I meant 9928 vs 9929. The long and short of it is, 9929 is RGB, we all know that. Swap the chip, and you have RGB. The 9928 is YUV.... which is actually the same as... YPbPr the analog version of YCbCr... With the previous work that has been done before, 5-11 built a board, to output YPbPr (component). However with my experiments, I can confirm, the "blue" is very slightly out of phase with the other 2 signals. Which is why there is a blue tinge to the black color in the picture. Using a pot, trim the blue output by about 92ohms and the tinge is gone. I'm waiting for this.... http://www.ebay.com/itm/141913950282?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT Wire pins 35,36,38 and ground and +5, and one should have a very cheap but effective HDMI out.... All connections would be direct, (Except for pin 35 to Pb, it would need a 100ohm trim pot)

Ok, So I will confirm this for some people. https://en.wikipedia.org/wiki/Texas_Instruments_TMS9918 The NTSC TMS9918 does output composite video. The question no one is asking is HOW. So let me clarify, it uses pins 35,36,38 to create a composite signal. That is then modulated to become RF out. The chip outputs what is known as "YUV". And yes, it is actually TRIVIAL to convert to RGB. All it takes is an LM1881 "sync stripper" and a high speed amp. See here for a schematic. http://www.labguysworld.com/YUV2RGB_Matrix.htm The reason I was interested in the SCART schematic, was I was interested in how the amp in the CBS version was built. As an aside, (I have parts on order to test theory), I believe it might be possible to convert the NTSC Coleco to HDMI for less that $40. (I know, outrageous claim... but 5-11 already did part of the legwork...) If it works I can post a video on how it works, for those that are interested.

So no one?

Does anyone have a circuit diagram of the french colecovision? I notice it has a SCART output. I'm interested for research purposes.

I find this even better than the grease, and it doesnt dry out. the 22a stuff... www.stabilant.com

Check out this auction, am I correct in assuming the Frogger II one is in the wrong case? I know he says they are from the UK, opinions? http://www.ebay.ca/itm/13-Rare-Never-Played-Games-for-Colecovision-Cartridge-Copied-Manuals-Only-/391432543540?hash=item5b23329d34:g:7UEAAOSwgApXDUWz

Hey dude, here it is...

Your the @#%#@$ man dude! I found 2 broken traces between VDP and CPU pin 19 & 20. (Most likely was me when I socketed the chips.) I have it back up and running!! I believe it was bad Vram issue to begin with. 2 fried chips. Thanks for your help guys! Goes to show if you work at it, they can be fixed!

Ok Nanochess, I dont have Frogger, but I do have a cart called Facemaker. which skips the BIOS and plays music on startup. This works! I hear the tone! So to me that means the CPU, SRAM, Clock circuit etc are all working properly. I'm dealing with a video issue? If I go straight to pin 36 of the VDP there is no B/W image. Yet if I check the VDP on the other machine, it works fine. I know the RF board is good, since I know if I plug expansion module #1 in I get video. So do you think the issue is between the CPU and VDP? Ideas?

Wow your on it Nanochess!! I thought we had it fixed... but sadly no... Ok, when I looked, I had voltage on pin 12 of U5 even with power off. (2.5). So I changed U5, and now there appears to be no voltage leaking. It has the same voltage readings as the working one. pin 11 starts low goes high and stays high. pin 12 starts low, goes high at power on, then blips low, but stays high. (same as working one) pin 15 clocks, I dont have a frogger cart but I'll fix that soon. Thanks for your help!

Thanks for your help Nanochess... I do have TTL logic probe... http://www.atarihq.com/danb/files/colecovision.pdf Z80 - Pin 6 - 3.58Mhz measured, Reset Pin 26 goes from Hi -> Low when reset button pushed. Mreq pin 19 has data. Goes high when reset pressed. Pin 22 seems to write data for a half second then stop... I'm not sure how to test chip selection?... 76489 chip pin4 has data too... There is NO tone... 10.74Mhz measured at pin 40 of VDP... There are 2 74ls138's do you mean U6 or U5? (I replaced U6 since it deals with the VDP) U5 pin 15 seems to have data is that bios chip selection?

Which decoders? U18 U19? I swapped out one of the 138 chips at U6, do you mean U5? I haven't touched the 74LS04 since I had a good clock signal, but I'll try that one next too...

The Vram had 2 bad chips, I pulled them all and socketed them. I had to pull them to test, (at least the way I could test) I checked the data bus lines and they all seem fine. I also swapped out U6 and U8, no change.... I did notice that U18 and U19 are connected to the data bus... D0-D7, I know those chips blow, I wonder if one of them is holding down the bus? I havent tried them, but it looks like the chips are available here... http://www.ebay.ca/itm/1PCS-LM1889N-TV-Video-Modulator-A615-LW-/171892149275?hash=item2805920c1b:g:7rAAAOSwu4BV4Tiq

Hey, hey, another from the great white north? (With a picture your farther ahead than I am, if you have B/W pic then your into the RF section. I'd go after the LM1889) Update, So, I've replaced/checked and confirmed the vram is all working. I still do not get the bios splash screen, However, I do get some letters and random patterns, when pressing the reset button. They stay on the screen frozen. Since I know the chips are fine (tested on other machine) I'm going to check the board wiring/pin connections on ram. There are only a few chips left, and since this board is mostly sockets already, might as well keep going.

Update, CPU Z80 is tested and confirmed working. VPU is tested and working. Audio 76489 is tested and working. Sram 2114 is tested and working. I have found a couple of bad Vram 4116 chips bad. Not sure if this would cause black screen, but once they are replaced, I'll update.

Thanks guys, I have tried 2 power supplies, same thing.... this weekend I pulled the pin and brought in a friends working coleco to test the chips on. (I know, scary) I confirmed the sram is good, audio chip, and the VDP chip is functional. I'm focused on Vram right now, however, on the last pages of the service manual, they show pictures of what it looks like when it's not working. It still shows the coleco bios splash screen. persistence is going to be the key...

Thanks for the ideas Nanochess, I'm still plugging away at it, there's not too many threads out there, with people who have fixed black screen / no boot Colecos... This thing still has me perplexed... It looks like all the VRAM pin 14 goes low, so I believe the BIOS has attempted to clear them. I have exchanged the SRAM, with no change, and the BIOS, with no change. I guess onward to the VRAM, soon all but the TTL logic chips will be socketed... Not sure why there's still no BIOS screen...

Sooo... Swapped out CPU have the same issue... So I guess It's on to the BIOS and the 2114 ram?... Buller... Buller... Anyone?...

did some more checking today pin 28 of the CPU RFSH does not cycle, always high.

ok, so I have exactly 10.74mhz on pin 40 of the vdp... pin 36 seems ok, I get black screen, however no coleco logo or insert cart message. On the CPU pin 27 M1 seems to stay low, like it's stuck trying to read from memory. CPU then BIOS?

Ok, so to update.... I have pulled and swapped the VDP, same issue. On to the processor...