vgcollector

I just wanted to verify I am checking the pins in the right way since this is reversed. Here is my assumptions for the pin locations.

Ok, here are my findings. Just to clarify I started with pin 1 on the right side of the chip, and then 40 would be in the top left. For signs of life, check pins 1 and 2 for blinking. In fact, everything from 1-9 ought to blink some. -1-blinking, 2-low 10 and 11 only activate when it's writing data to a chip. So unless a game is in the middle of playing, 10 and 11 are uncertain. -didnt test 12 is ground, so should read low. -Low 13 comes from the CV's address bus and will probably be blinking as a matter of course.- Low 14 and 15 are select inputs from the CV. They will be reading high unless it's actually talking to the chip.- 14- blink, 15- low 16 goes low whenever vertical retrace happens, but only when the interrupt is enabled by software. I would expect it to be constant high for this situation. But if it's blinking, that's acceptable. - Low 17-24 are the system data bus, so you should see blinking on all of those.17-19 blink, 20-24 blink, 25-32 will be dependent on VDC reading memory. I suspect them to be pretty quiet unless a game running-Didn't test. 33 is the +5 supply and should read high. - Low 34 is an external reset input and should read high. -Low 35, 36, and 38 (note that we skip a pin here) are the video signal outputs. They are analog, so the probe will probably not give you any useful indications from them. -didn't test 37 is a clock output. The CV leaves the pin disconnected, but it ought to be blinking. Blinking 39 is also disconnected but will probably be blinking if you probe it. Blinking Finally, 40 is the clock input. We already tested it from the clock generator, but you could check it here at the input just to make sure it didn't get interrupted on the way.-Blink Let me know what you think of these readings. The Pin 33 & 34 were the ones that stood out to me. Thanks for the quick replies. I am probably done testing for the night, but let me know what direction you would like me to test or re-test.

Ok thanks. I thought I had it right, but I wanted to make sure because if I wasn't I needed to find out now. ChildofCV, I checked all the readings on the chips and they match up with what you had above for chips U22, U8, and U7. I was really hoping one of these would have showed us some failure. What should I check next? I am really learning some new stuff, and thank you to everyone who has responded to this post. Hopefully at the end I will have some kind of procedure that will help anyone who gets the black screen issue when you switch on the Colecovision. I am good at documenting fixes.

Finally got brave and hooked up the logic probe. Now I want to make sure I am numbering the pins correctly. From the top of the chip using U22 as an example. I have 14 pins total. I read that the numbering sequence is in a counter clockwise order. So looking at the top of the chip where it is labeled U22. The pin 1 is on the left goes down the left side 1-7. Then 8 starts from the bottom of the right side of the chip and goes up along the right side 8-14. Am I numbering the pins correctly?

HI, I recently purchased the Ultimate SD Colecovision cartridge. I have a Colecovision with a bad memory chip. I ran the diagnostics using the cartridge and I received a failure code on the VRAM of 0x7143 [71,BF]. However I can't find any diagnostic codes that will help me identify which chip is bad. If you are familar with the test, I get the first white video screen and then I get the error. I appreciate any help. I have looked for this code or even part of it, but I can't find anything in the documentation I have found so far. Thanks

Ok, thanks. I see what you are connected to now. I couldn't see the tip of clip connected until you told me where it was connecting. Thank you again. I will let you know what I find. I hope to get this done in the next couple of days.

Great picture. The black clip is attached to the frame of the power switch, but what is the red clip attached to? I appreciate the detailed picture. I just want to make sure I am doing it right.

Getting closer to using the probe, but I don't want to damage it from the start. If you were using the logic probe on the Colecovision where exactly would you connect the black and red clips.I am looking for specific locations so I connect them to the correct spot. Thanks again for your help.

You had it right. I have one working one and then 3 with the same black screen issue. Thanks

I have used the tv set with my working Colecovision and it does fine. I am pretty good at eliminating problem possibilities.I use my good Colecovision to test the RF cable, TV, and power supply. I hope to test with the logic probe before the end of the week. Thanks for your assistance. Vgcollector

ChildofCV, thanks for your help. I am working on some other things, and then I will get back to the Logic probe. Have you heard much about the Atarimax for the Colecovision? I am thinking about getting one because it has the Colecovision diagnostics. That would be helpful in testing the memory. Thanks, I just wanted to let you know what I was working on. Vgcollector

One other question from this newbie about using the logic probe. Do you test this with the power switch on? If turned on, do I need a cartridge in the slot.? I plan to try it out tonight. FYI I did test with the Frogger cartridge and I got no sound. That oscillator may be the culprit since you said it starts everything else. Thanks, Vgcollector

Where should I plug in the red clip? I will try and do this today or tomorrow. Thanks for the specific information. Vgcollector

Do you know if I can attach the black lead to the +5 on the power plug in on the Colecovision and the red lead to the -5? Then do you know what pins to check on the chips? Thanks, Vgcollector

I went and bought a logic probe. Now I will have to look at some youtube videos to learn how to use it. Are you able to test most of the Colecovision chips with this? This could be a real game changer if I am able to find a bad chip with it. You have been most helpful. Thanks, vgcollector

You really have put a lot of time into this. Thanks for all the great documents.I can pretty much fix the controllers, the Super Action Controllers, the roller controller, and most issues with the Atari Expansion module. I am still working on my skills with the driving controller. This one issue is one of the few that I have not been able to isolate, but it would be nice to be able to come up with a check or checks that would identify which chip or chips are failing. I am an electronics novice when it comes to things like voltages and knowing what a chip does, but I am good at troubleshooting. De-soldering the chips on the pcb are tough. I have done the controller chips, and the memory chips, but that is about it so far. Is there anything out there that will allow you to test each chip for voltages to make sure they are getting or putting out the correct readings? Thanks, Vgcollector

Do you know what chip number it is? This would explain a lot. Is there a way to check voltages on that chip to make sure it is working properly? This is excellent information. I appreciate you sharing this!! I am going to try and put together a lot of the info out there specifically related to the CV motherboard like what is the function of each chip number. That will help me and others identify problems with the chips for troubleshooting. Thanks, Vgcollector

I will look for the oscillator or crystal. What is the function of the oscillator? Thanks, Vgcollector

I will try the Frogger that is a good idea too. Thanks I appreciate all the suggestions. Vgcollector

Thanks for the information. Here is what I have done so far. Tested power supply for voltages and they all check out. De-soldered power switch cover and cleaned the power switch. I do get video and audio using the Atari Expansion Module so the RF should be ok. Cleaned cartridge slot and checked for anything in the slot. When turned on, the screen is black and sometimes has a hum which varies from time to time. This happens regardless if a cartridge is in the slot or not. I have 3 Colecovisions doing this same thing, Most of these boards seem to be in good condition and one Colecovision was super clean so I was surprised when it didn't power up correctly. I appreciate the help with this one. I know this issue has been brought up in these forums before, but I have never seen a clear cut solution. I am a novice on the electrical stuff and some of the terminologies, so I appreciate the clarifications. Thanks, Vgcollector

I found the Y1 connector on the 74LS138 chip. So did you have to resolder the chip? I just want to make sure I know that your terminology when you use the word "leg: are you referring to one of the pins of the chip? Thanks again.

Hi, thanks for the tip. Where is the Y1 located on the system board. I looked for it but couldn't find it. Thanks for your comment. I just saw it.

Hi, I am new to this forum but I have been collecting and repairing video game systems for a while now. My favorite system is the Colecovision. I have learned a lot about how to fix broken ones. However, I have not been able to fix the black screen issue. I always clean disassemble the power switch and clean it and resolder it. This fixes a lot of issues. The one thing that stumps me is black screen issue where when powered on your Colecovision displays a blank black screen sometimes with a hum. Has anyone come up with the steps to try and fix this? I am not the best at checking voltages, but I do have a voltage tester, but I don't know what pins to check. If anyone can help it would be much appreciated. I have read a lot of forums on this subject, but very few end with the fix. Thanks in advance.