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Need help with SECAM (French) Colecovision


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#1 zCRP OFFLINE  

zCRP

    Space Invader

  • 23 posts

Posted Sun Sep 24, 2017 11:11 AM

Hi All,

 so I got hold of a French CV (board model 91209 rev B), thinking that given its built-in RGB support it would be a good replacement for my current av-modded PAL model.

 

Upon receiving it I turned it on, and despite being in bad shape (extremely dirty) it started correctly, and I immediately saw a sign of bad vram chips (there was character corruption exactly like described in the technical manual). Apart from this the unit looked fine. So I took it upon myself to install replacement vrams (I bought a bunch of MB8118-10 chips) doing the 5V mod at the same time. I removed coils L2 and L3, and the left pin of L3 to a 5V source nearby.

 

Then I turned on the CV (without cart) and got a black screen. I turned it off again, inserted the Q*Bert cart, and back on. Now instead of a black screen I get a blue screen, no chars or anything else, just blue. I can hear the initial jingle and if I press 1 on the controller the game appears to start, but hangs shortly after. the screen is now black again and in the middle of the screen there is a single yellow artifact. For all that I know it might be a sprite. But at the point the CV is frozen, no sound, and no way to do anything else save resetting and going back to the blue screen.

At this point I also socketed the VDP and two ram chips, and tried installing replacements that I have sitting around, but to no avail.

 

I checked and rechecked all the solderings, and did continuity tests between all vram chips and the vdp, and everythin appears in order. Successively I also decided to deep-clean the board by washing it in a dishwasher and drying it in the oven at 65C. But nothing changed, still same blue screen plus freeze.

 

The next step I would try is to reflow the whole board by placing it into an oven at 250-300C, that might maybe fix any soldering issues.

 

Does anyone have any other suggestion on what is going on and what I might try before throwing the board into the oven? I have also ordered 2 replacement Z80A and will try to install that and see if it makes a difference. At this point almost the whole board is socketed save the bios, the sound chip and the various 74LS... chips. I do not have an eeprom programmer so I have no way of replacing the bios chip.

 

Side question: on the board there is a trimpot. I have not seen any of these on ntsc or pal boards. Any ideas what it is for?

 

Thanks

Chris



#2 zCRP OFFLINE  

zCRP

    Space Invader

  • Topic Starter
  • 23 posts

Posted Thu Oct 5, 2017 1:42 PM

Anyone?



#3 zCRP OFFLINE  

zCRP

    Space Invader

  • Topic Starter
  • 23 posts

Posted Sun Oct 15, 2017 9:08 AM

I have socketed the whole board and replaced *all* ICs (bios chip coming from a working CV). The CV still will not work. Can anyone please give some suggestion on what I might try next? I do not have an oscilloscope but I do have a logic analyzer. Can I use that to check if signals are good, as stated in the tech manual? What should I look for exactly?

 

Many thanks for any help!!!

 

PS: the power supply is fine and works with a different unit. the switch is fine as well.


Edited by zCRP, Sun Oct 15, 2017 9:14 AM.


#4 Pixelboy OFFLINE  

Pixelboy

    Quadrunner

  • 7,725 posts
  • Location:Montreal, Canada

Posted Sun Oct 15, 2017 10:33 AM

What does the cartridge connector look like? If there are any worn pins inside the cartridge port, that could explain your troubles.

#5 omf ONLINE  

omf

    Dragonstomper

  • 729 posts

Posted Wed Oct 18, 2017 5:49 AM

you

 

I have socketed the whole board and replaced *all* ICs (bios chip coming from a working CV). The CV still will not work. Can anyone please give some suggestion on what I might try next? I do not have an oscilloscope but I do have a logic analyzer. Can I use that to check if signals are good, as stated in the tech manual? What should I look for exactly?

 

Many thanks for any help!!!

 

PS: the power supply is fine and works with a different unit. the switch is fine as well.

you might try examining the crystals, one may not be connected on one of the pins,  a crystal that is connected by only 1 pin is rather useless and will give you a permanent black screen.

 

you may have hit it by mistake when doing the mods you have done

, failing that you have probably damages a board trace so that it is not connected, inspect all the ram chips and make sure that all pins of the chips can be reached by the joining traces, so test at the other end of themand the chip pin leg






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