SNES Repro works on one SNES but not other

snakestersnakester
in Help Wanted!
I am wondering if anyone has ever encountered an issue like this. I am using a Retrostage Megarom 2.0 board and on my SNES Jr it works perfectly. On my other SNES it will start but will turn off within a minute, at different intervals but always within a minute. The red light is still on but the screen blanks and goes to a blue screen and says no signal. Original SNES games and repros I have made with donors work on that console but not the retrostage one. Any help would be greatly appreciated. Thanks in advance. 

Comments

  • MrPete1985MrPete1985
    You are getting cross talk on the CIC lines and it is causing the game to cut out. The earlier model are more prone to this than the later models



    I had some customers report the same issue when I was using the Retro Stage boards, I switched to Marks boards and my customers said they played fine

    https://www.mortoffgames.com/super-nintendo-/homebrew-equiptment/boards



    Mark's board have the SuperCIC closer to the cart edge with more ground fill to prevent cross talk.
  • snakestersnakester
    Thanks for letting me know. I thought it was something wrong with my console or not enough power going thru the board but tested Lo and Hi rom, ram and no ram. All seem to have the same problem. Do you know if I can hand wire anything to bypass the problem? So far tested 6 of these and all are doing the same thing. I'll have to go to mortoff for my next batch of SNES boards. 
  • MrPete1985MrPete1985
    Well it is an issue with the layout and trace routing on the board. Maybe if you bend up the data pins on the SuperCIC and ran wires to the cart edge that might help but I am not sure.



    Installing a SuperCIC in your console might fix the issue also but if you take them over a friends house you might run into the same problem again.
  • snakestersnakester
    I tried cutting the data traces and wiring to the edge connector worked for a little longer but still shut off within 5 minutes. Was trying to fix it because half of them were going to my brothers and he only has the original SNES.
  • MrPete1985MrPete1985
    There are a few different revisions of the big SNES, I am not sure the exact models that are affected so it might play on his or it might not.



    Best advise I can give you at this point would be see if you can return them and pick up some of Marks boards.



    Retro and I went back and forth for a while when this happened to my customers, we thought it was caused by a bad batch of 22uf caps that I got that were measuring out of spec. After replacing them with new ones I sold a few more and that the issue was solved but then got another report. At that point Mark's boards were on the market so I just switched to his exclusively.



    It was Mark that told me about the cross talk issue as he had ran into it during his prototype phase.
  • snakestersnakester
    I am going to have him test it tonight. Thank you for all your help. I will definitely be picking up some of Marks.
  • RetrostageRetrostage
    Originally posted by: MrPete1985



    There are a few different revisions of the big SNES, I am not sure the exact models that are affected so it might play on his or it might not.



    Best advise I can give you at this point would be see if you can return them and pick up some of Marks boards.



    Retro and I went back and forth for a while when this happened to my customers, we thought it was caused by a bad batch of 22uf caps that I got that were measuring out of spec. After replacing them with new ones I sold a few more and that the issue was solved but then got another report. At that point Mark's boards were on the market so I just switched to his exclusively.



    It was Mark that told me about the cross talk issue as he had ran into it during his prototype phase.

    It's not actually cross-talk at all. It's a matter of the 74HCT chips being used on certain consoles, from what I figure is weak power/flakey caps in the console.



    If you switch out the HCT series for the LS series then the issue is resolved. 100% of the time.



    The CIC is not the culprit here, which is why it works perfectly fine on some consoles. If it was cross-talk due to a board problem then it would happen on all consoles.



     
  • MrPete1985MrPete1985
    I still think it is the a CIC issue. If you put just the CIC into a board and put it in the SNES you will get a black screen, without a CIC the SNES will not even attempt to output an image. If the issue were with the HCT parts then the SNES should at least have a black screen rather than getting a no video input message from the TV.



    The boards I linked use all HCT parts.
  • snakestersnakester
    Just tested it with a LS139 and 2 HC 257's and it seems to be working in the other console. I was originally using HCT139 and HCT 257. I tested with a game genie just to see and that made it do the same thing as before on the older console. Going to order the LS 257 and try that but I think that's the fix. Since the game genie did not work on either console with the HCT but works with the Ls and HC on the JR console. Relieved it wasn't my console at first when I posted I thought that my console might be putting to much power into the cartridge.
  • RetrostageRetrostage
    Great to hear, if you run into any other issues please PM me directly.
  • MrPete1985MrPete1985
    What exactly is the difference between the HCT and LS chips, looking at the data sheet I am not seeing why one would work and the other would not
  • wiggyxwiggyx
    Originally posted by: MrPete1985



    What exactly is the difference between the HCT and LS chips, looking at the data sheet I am not seeing why one would work and the other would not



    It doesn't seem like it would matter, but this is indeed the issue.  I ran into the same issue a couple of years back.  Retrostage recommended that I make the switch as well and that particular issue never came up again.

     
  • RetrostageRetrostage
    Originally posted by: MrPete1985



    What exactly is the difference between the HCT and LS chips, looking at the data sheet I am not seeing why one would work and the other would not



    Look at the voltage and timing between the two chips.



    For comparison, I checked out Texas Instruments 74HCT139 and 74LS139, respectively. It may differ slightly between brands, but it should be close. All values below are when operating at TTL levels.



    74HCT:

    VOH 3.84V minimum during H level outputs (no typical values in sheet)

    ~43ns transition time from inputs to outputs, as well as enable transition



    74LS:

    VOH 2.7V minimum (3.4V typical) during H level outputs

    ~33ns transition time from inputs to outputs, as well as enable transition



    It may not seem like much, but 10ns is a huge difference in timings for electronics. And over a 1V difference (at minimum levels) between high output (VOH) draw between them. That's a pretty big difference.
  • MrPete1985MrPete1985
    Definitely an odd issue. Glad I am wrong and it is an easy fix.



    Sorry for bashing your boards Retro. Has your documentation been updated to note that HCT parts are not compatible? I know the guide I put together for you says that HC, HCT, and LS will all work, that part will need to be updated.
  • RetrostageRetrostage
    ^^ Yes, PDF has been updated with links to the LS series in the parts list, as well as a recommendation to use them over the HCT.
  • NeoGeoThaiNeoGeoThai
    I got the same probleme here.

    Made 2 repros with Megarom 2.0 boards : Wonder Project J French version and Seiken Densetsu 3 French version, both games crashed/black screen randomly on Super Famicom. (I tested the games on 3 different SFC).

    So I desolder all HCT parts and replaced them with LS parts, but still got randomly crashes.

    The only way I get a stable game is to use my repros through the AD29 adapter !!



    For me it looks more a CIC problem rather then a HCT/LS problem.
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