vgcollector
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Posts posted by vgcollector
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Big Ben, on the Atari expansion module if you get a blank screen when plugged in there are a couple of things to check. First clean both the expansion port connector on the Colecovision with some alcohol and do the same for the expansion module connector. If you are comfortable taking things apart, remove the expansion module cover. Then remove the little zif connector ribbon from its slot, clean it as well and reinsert it.
** Please do all of this with the power cable unplugged.
Hope that helps. ChildofCV was very helpful to me when I tried to fix my black screen issue with my Colelcovision. I never got it working, but he was a big help!!
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I finally got back to this. I apologize for the big gaps right now, but my son plays college baseball so during the season I don't have as much free time. I replaced controller chip for player 1 with no change. I have it socketed so I can pull it easily. What is the best location to check with the logic probe to check for the short to ground. I will busy for a couple more weeks and then I should be able to get back at it a little more frequently. Thanks
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Ok thanks, I will start looking at those. Does it matter which one I do first? I have a couple of sets of these.
Thanks
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I meant the SRAM, sorry for the confusion. I will try the U4 chip first, and then see what happens. Hopefully I can get this done in the next few days.I will update you when that's done hopefully with some good news. Thanks!!
Thanks
I replaced the U4 SRAM chip with no change. I am going to change out the U3 chip next.It will probably be later in the week before I have time to do this.
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Well, first we need to clarify some terms. VRAM is the 8 video RAM chips above the video chip. It's actually DRAM (dynamic RAM), but since it's used for video they call it VRAM.
SRAM (static RAM) are the 2 chips below the video controller. They are also the 1K system RAM, so I guess you could still call them SRAM.
In some circumstances, the video RAM can be the fault, but in your case the problem is long before data can even reach the video controller, let alone the VRAM.
That said, the SRAM certainly can be the problem. U4 is the one that connects to the faulty data line (each byte of system RAM is divided so that U3 gets the low half and U4 gets the high half), so it would be the first one I tried. U3 is not connected to the faulty data line, so cannot be its cause (but of course it can still be dead...). But for now, resurrecting the D4 data line between those named 7 chips is the priority. If the RAM chip doesn't fix it, I'd move on to the input chips since they can be abused by static shock and are standard 74LS series chips, therefore easily replaced.
I meant the SRAM, sorry for the confusion. I will try the U4 chip first, and then see what happens. Hopefully I can get this done in the next few days.I will update you when that's done hopefully with some good news. Thanks!!
Thanks
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That would be the left side of C88 at the top of the board.
ChildOfCv, I finally got back to my little project of fixing the black screen issue. I have ordered some new VRAM chips, but while I waited I went ahead and desoldered 2 good working ones from a Colecovision board I got that someone had butchered and it powered up correctly, but the controller ports an traces were shot. So I removed the 2 VRAM chips from the board. Now based on your comments about D4 being held down above. Do you think I should just replace the U4 vram chip and then see what happens. Then if I need to I can replace U3 as well? I have read a lot of the fixes for the Black screen issues and even though a lot of the topics never post what the solution is, a lot of them seem to point to the Vram. I think it has to be something that is fairly common with all the Colecovision boards. Thanks, my soldering skills are slowly improving.
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I was going to ask you what pin can I put a set of ear phones on to hear music if I have Frogger is inserted. I have seen on the forum you can do it, but they don't mention which pin.
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And this is the signal line that is supposed to activate the ROM chip. You said that it is blinking on U5, but not on U2?
ChildOfCv, I appreciate all the help you have been!! I have learned a lot and I will keep posting with progress. I think I may just change the ROM chip to start since I have 2 brand new ones I got from Console 5. I will check the readings on U2 and U5 again to make sure I got them correctly. After the first couple of chips I tested I pretty much tested every chip 2-3 times to make sure I got a good reading. Do you have any kind of document that says what the reading should be on most of the chip pins on a working Colecovision. I do have a working one, and I may just crack it open and take the readings off each chip for comparison.
If you have any part#'s for Colecovision chips you have ordered from Digikey or Mouser please let me know. I can identify chips that are the same, but then they have all the extra letters and I get lost.
Thanks, I will post as I have updates.
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Well this is weird again then.
U5 seems to be working as it ought to: The address consistently lies in the ROM region, and it is indeed attempting to activate the ROM chip. Pin 15 is electrically connected to U2 pin 22, so it also ought to be showing the same readings. With power off, check continuity there. Hopefully this is another miscounted pin thing.
Anyway, it appears that the biggest issue is that something seems to be holding D4 down. Unfortunately, there are 7 chips that connect to this pin: U1, U2, U4, U9, U18, U19, U20. Then there are the expansion ports and the cartridge port. I assume you've already given the cartridge port a close inspection? Also, take a very close look at the top right side of the expansion port, as D4 is in that area too. You should get a resistance reading of any D4 connection to ground, such as U2 pin 20 or U4 pin 14.
As far as which of the 6 is the source of the problem, well here's where desoldering skills come in. I would hope for one of the common chips. U18 and U19 could be destroyed by static while plugging and unplugging controllers, for instance. U4 is a RAM chip, and "stuck bits" are synonymous with RAM, but this is a slightly unusual case that hopefully doesn't involve the RAM. But it's still a logical choice. Anyway, you may need to remove them one by one in order from most likely to least likely, until the short (that I suspect is the problem) goes awa
First, where is a good source of replacement chips? I have a ROM chip, controller chips, and the newer DRAM chips, but I haven't found a place that sells the others except for China on ebay. Also when you refer to D4 what are you referring to there.
If you were doing this what would you replace 1st? I can solder, but I was hoping to narrow it down some. Does the fact that the Expansion module work eliminate any of the chips you listed above. I appreciate all the help you have been. I have learned a lot.
Thanks,
Vgcollector
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One more thing: could you try hitting reset a few times while holding the probe on 22 to see if there's at least a blink of access?
I did this and it blinked each time I hit the reset button.
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The test above was for U2. Testing U5 now.
Ok, tested the real U5 16 pins.Just to clarify the first set of readings is for U2, and the 2nd set is U5.
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I tested CPU pin 22 and it was High, no blinking, and High tone. I tested the U5 chip and mine had 24 pins(short chip) so 1 and 2 were empty as well as pins 27 & 28. So just to clarify the first chip I did the reading on was #3. Let me know what you think of these readings. Thanks
The test above was for U2. Testing U5 now.
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Sorry I didn't see your reply to my post I will check these tonight. I usually get an email on new posts, and I didn't check.
Thanks
I tested CPU pin 22 and it was High, no blinking, and High tone. I tested the U5 chip and mine had 24 pins(short chip) so 1 and 2 were empty as well as pins 27 & 28. So just to clarify the first chip I did the reading on was #3. Let me know what you think of these readings. Thanks
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Sorry I didn't see your reply to my post I will check these tonight. I usually get an email on new posts, and I didn't check.
Thanks
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So on the test you see the first screen with the white stripes on it and then on the next screen it fails? That next screen should be the color test. Also can you post a pic of what your Colecovision main logo screen looks like without a cart plugged in assuming that comes up looking goofy?
Thanks for the reply!! The unit works fine, but it has a screen glitch on Donkey King on the 2nd & 3rd screens where one block isn't displayed correctly. Everything else is fine.
Thanks,
Vgcollector
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Hi, I tried to copy the U3 & U4 second readings list from my spreadsheet but it wouldn't let me attach it or copy it in. I have attached a snip it of what my findings were. Let me know what you think.
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Yes, definitely make sure the pins are connected with an ohm meter (power off).
At the moment, I don't have a strong suspicion about any of the chips until we see the re-check of the pins. But if you really have activity on all the data pins at the memory chips, but nothing at the VDC on that one pin, then that does mean there is a trace breakage somewhere.
Just fair warning: The PCB traces I showed were my own routing and do not necessarily match the board. I routed the traces in order to compare every connection manually. But without removing large chips, I couldn't see those parts of the board well enough to run the traces exactly as they were. But the pin connections themselves will be correct.
Sorry for the late post on this, but here are my latest readings on U3 & U4. I put these into Excel so I could concentrate on the readings.
Second Test Chip U3 Chip U4 Pin# Low/High Blinking Tone Pin# Low/High Blinking Tone 1 Both Yes Low 1 Both Yes Low 2 Both Yes Low 2 Both Yes Low 3 Low Yes Low 3 Low Yes Low 4 Both Yes High 4 Both Yes High 5 Both Yes Low 5 Both Yes Low 6 Both Yes High 6 Both Yes High 7 Both Yes High 7 Both Yes High 8 High No Low 8 High No Low 9 Low No High 9 Low No High 10 High No High 10 High No High 11 Both Yes High 11* Low Yes Low 12 Low Yes Low 12 Low Yes Low 13 Low Yes Low 13 Low Yes Low 14 Low Yes Low 14* Low No High 15 Both Yes Low 15 Both Yes High 16 Both Yes Low 16 Both Yes High 17 Low No High 17 Low No High 18 High No Low 18 High No LowI put an asterisk next to the readings on U4 that were way different than U3. Thanks. I was a little more precise this time.
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One other question. If there is a broken trace, am I looking for the break on the top of the board or on the bottom. I figure I might as well check the traces while I am testing the pins.
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I have not seen any evidence of prior work on this board. All of the solder joints seem to be original. I think I could spot that especially as close as I have looked at this particular board. I will check those spots tonight and update my post when I get that done. I will also look for broken traces. I would think that a broken trace wouldn't happen with the board seated like it is. Is there any chip you are leaning towards as being the culprit yet? Thanks
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Hmmm... there are a couple of things off here. First of all, pin 8 is electrically connected to both chips. So unless there's a bad trace on the motherboard, you should not see any difference between reading the chips. Also, you show all data lines working here, which makes it hard to believe one would be dead on the TI chip. Here's a diagram of the chips to help:
Gd CS A2 A1 A0 A3 A4 A5 A6 9 8 7 6 5 4 3 2 1 +-------------------------+ | _| | (_| | | +-------------------------+ 10 11 12 13 14 15 16 17 18 WR D3 D2 D1 D0 A9 A8 A7 +5
Now, it isn't impossible to see the above happen... if the board is cracked and the traces are broken in some area. But for now I'd like you to double-check the readings. And if you do see blinking on all of the D lines above on both chips, re-check pin 21 on the VDC. It should be connected to pin 14 on the lower memory chip.
Thanks for the pictures. That helps to see how they are connected. I will redo these readings tonight.
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With a dead data bit, I am beginning to suspect memory chips. The CPU only does what it's told, and without good memory it's going to be told some really funky stuff. Could you give me a reading on U3 and U4? I'd offer my expectations, but I need to be somewhere. BBL.
I tested U3 and U4. I did want to let you know that on this one I got some different readings and tones. I will try to describe what I saw on the probe as well as I can.
U3
1-low/high lights lit blinking low tone
2- low/high lights lit blinking low tone
3- low/high lights lit blinking low tone
4- low/hgih lights lit blinking high tone
5-low/high lights lit blinking low tone
6- low/high lights lit blinking high tone
7- low/high lights lit blinking high tone
8- low/high lights lit blinking high tone
9- Low
10-High
11-Low Blinking
12- Low Blinking
13- Low Blinking
14- Low Blinking
15- Low Blinking
16- Low Blinking
17- Low
18 - High
U4
1- Low/High lights lit Low tone
2- Low/High lights lit Low tone
3 - Low light lit Blinking
4- low/high lights lit blinking high tone
5- low/high lights lit blinking high tone
6- low/high lights lit blinking high tone
7- low/high lights lit blinking high tone
8- High
9- Low
10-High
11- Low lit Blinking
12- Low lit Blinking
13- Low lit Blinking
14- Low lit Blinking
15- Low/ High lit Blinking
16- Low/High lit Blinking
17- Low
18- High
I hope this is clear to you. I don't know if you have a spreadsheet with all these readings, but I was thinking about doing the readings on a working Colecovision and then comparing it to what we are finding with this broken one. I think a spreadsheet might be helpful in organizing all of this. Thanks
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Hi, thanks for the additional conditions to check so we are both on the same page. I will test all of these conditions on the Colecovision I am working on. I will test these and then test the pins on VDC again. It will be later this afternoon as I am not home right now.
Thanks
Ok, here is my latest testing results. I verified power voltages are correct. I plugged in Frogger, no sound. I plugged in Atari Expansion Module, got picture and sound.
With Frogger plugged in cart slot
U9 Results- Exception indicates does not match your expected results
Pins 1-8 – Blink
Pin 9- High- Exception
Pins 10 & 11- didn’t test
Pin 12 – Low
Pin 13 – Blinking
Ping 14 & 15 –High
Pin 16 – High- Exception
Pin 17-20, 22-24 – Blinking
Pin 21 – Low- Exception
Pins 25-32 – Didn’t Test
Pin 33 – High
Pin 34 – High
Pins 35, 36, & 38 – Didn’t test
Pin 37 – Blinking
Pin 39 – Low- Exception
Pin 40 – Blinking
U6
Pin 1 – High
Pins 2-3, 6- Blinking
Pin 4 – High-Exception
Pin 5 – Low
Pin 6,7 – Didn’t test
Pin 8 – Low
Pin 9 – High – with Frogger plugged in- Exception
Pin 10 – High
Pin 11 – High- Exception
Pin 12 – High- Exception
Pin 13 –High- Exception
Pin 14 – High
Pin 15- High
Pin 16 - High
FYI, I saw in the CV technical manual that if you have a black screen after playing for a while, check the polarity of C106 which is a 10 uf tantalum. How do you check polarity. This may have nothing to do with the issue but just wanted to tell you I ran across it. It says to replace it if the polarity is wrong.
As always I appreciate the Help!!
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Hi, thanks for the additional conditions to check so we are both on the same page. I will test all of these conditions on the Colecovision I am working on. I will test these and then test the pins on VDC again. It will be later this afternoon as I am not home right now.
Thanks
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The indentation for that chip is on the right, so by the diagram above, you have the two backwards. Also, remember that the pins go counter-clockwise. So pin 1 is upper right, pin 20 is upper left, 21 is lower left, and 40 is lower right.
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 +---------------------------------------------------------+ | | | _| | {_| | | | | +---------------------------------------------------------+ 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40Ok, sorry, I misunderstood what you were saying about the pin numbering being the opposite on this chip. I will retest tonight and post my readings. FYI, I am doing all these tests with power on, a cartridge inserted, and 1 controller plugged in port 1. Is that how I should be testing?
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Black Screen issue with Colecovision
in ColecoVision / Adam
Posted
I just haven't had the time to work on this at all. ChildofCV was a great help to me but I was unable to isolate the problem. My soldering skills are decent, but I wasn't sure if I was replacing bad modules and then maybe not soldering or removing chips without causing more issues. It might be a while before I get back to it. Thanks for checking.