8 replies to this topic

[gibs]

Hello guys,

I have ordered a Colecovision that worked the time of a donkey kong game, then the screen has started to scramble.

1/ I have installed sockets on all RAM modules and the Video chip.
http://dl.dropbox.co...co/P1030274.JPG

2/ I have a ZX Spectrum 48k socketed, and fully working.

I tried the RAM from the Coleco on the ZX Spectrum and it's working perfectly.
I also did a : Print peek 23732 + peek 23733*256 wich return 65535
I would say that the RAM from the Coleco are OK

So I tried to put the 4116 of the Speccy into the Coleco.
I get a screen like this :
http://dl.dropbox.co...co/P1030276.JPG
http://dl.dropbox.co...co/P1030275.JPG

If I put back the Original RAM modules I have another scramble design (you'll see later).

3/ So I thought the Video chip was dead as on the schematics it is addressed by the RAM.
I have replaced the TMS9929ANL > Same result.

The console is able to run a game with sound (original RAM) :
http://dl.dropbox.co...5/Coleco/01.m4v

Here is what happen when I press the RESET button :
http://dl.dropbox.co...5/Coleco/02.m4v

And here is what it does sometimes:
http://dl.dropbox.co...5/Coleco/03.m4v


So I have read the FAQ and I have seen that the power button can be faulty.
I tried to clean it with Soft Air + Contact Cleaner but the console is still not working.

I would give a try to change the 10uF capacitors (maybe they are dry?) and replacing the Power button (Do you think it is really usefull after seeing the videos?)

Any tips are welcome. Thanks for reading.

[gibs]

What I have tried since my 1st post :

I can't get a screen like on my fist post anymore (now the screen is totally scrambled and then 15 sec after, it goes to a Blank signal (no signal) on TV)
It doesn't surprise me. I had "no signal" before going on holliday, and back from holiday the console was runing with the scramble screen again.
Games aren't running anymore too.

1/I have soldered the power switch to ON. Same result, so replacing the Power button will do nothing.

2/ I put back the 4116 of the speccy inside the Coleco.

Now, something interesting : when I power the console one, the screen scrambled but when I hold the reset button, I can get the perfect "Welcome" screen.
What does it means ? Does it means that my Bios chip is ok ? see here : http://dl.dropbox.co...5/Coleco/04.MOV

Thanks for reading.

Edited by gibs, Tue Aug 23, 2011 11:20 AM.

[5-11under]

Hi gibs,

First of all, welcome to AtariAge.

Usually, I've found that if the results are consistent, it's a RAM problem, and if the results are inconsistent, it's a power switch problem. Other options that you could consider are that the TMS9928A is faulty, or perhaps that the standard reset (on power-up) is too short, and needs to be lengthened (try powering up with the reset button pressed, then quickly release it).

One thing to remember is that the 4116 chips want to see the -5V active before the other voltages appear. With the power switch "shorted", the -5V won't get a head start.

[gibs]

Hi 5-11under,

Thanks for the information.

-Maybe I forgot to tell that I tried with another TMS9928A, and the result is the same (not better, not worst).

-Now, each time I power the console, I have a blank signal, and I need to do a RESET to have the red garbage screen.

here are some facts:

* In the previous video (http://dl.dropbox.co...5/Coleco/04.MOV) I could see a perfect welcome screen when I was holding the Reset button.
That was with the 4116 that were on my ZX Spectrum.

* I tried to put back the 4116 that were in the Coleco.
The result is : I have no signal at Power-on and when I hold the RESET button I can't have a perfect welcome screen.
The screen has some glitches like in this new video : http://dl.dropbox.co...5/Coleco/05.MOV

I tried the tip (powering up with the reset button pressed, then quickly release it) but no differences.

I don't understand why both set of RAM are working on my ZX Spectrum.

I have unsoldered & unmounted the Power Button to clean the inside (doesn't work better), I have ordered 2x SN74LS541, I have also socketed the Z80.

Any ideas ?

[gibs]

When I power up the system, I have -5V,+5V,12V at the 4116. I would say that my power switch is OK.

[gibs]

Hello guyz,

As I have different results with my set of RAM. I have purchased some NEW ram modules. I found exactly the same model that was installed on my Coleco.
I'll try as soon as I receive them.

If somebody has an idea of what's going wrong with this coleco, drop a message.

[gibs]

I come back with some clues.

As I said in my previous message, I have a garbage screen, but a proper screen when I hold Reset.
Using the oscilloscope, I have noticed that I have this signal on the collector of the Transistor Q23 close to the video connector.



When I hold the Reset button, the signal is cleaner like this :



I guess this is the signal I should have even when I don't hold the RESET button.

I have traced a bit and it appear that the Signal is also present on Pin 5-6-13 of U30 (HEF4066BP) and Pin 6 of U29 ((HEF4066BP).

Need to check the datasheet of those commutators.

Edit: Here is the Datasheet http://www.datasheet...s/HEF4066BF.pdf
Again, it's a PAL Colecovision.
On the Colecovision datasheet it seems there is only 1 HEF4066BP which seems to be my U30 because it's directly linked to the transistor collector. (Q23 on my board / Q3 in the schematic)
PIN6/U29 is also connected to PIN(5.6)/U30 which is linked to Pin13/U30 : Make sense.


If you have some ideas...you're welcome.

Edited by gibs, Sun Aug 28, 2011 8:57 AM.

[gibs]

SUCCESS !!!!!!!!

I'm happy to inform you that I have successfully fixed the Colecovision.

So...What I've done...

First I tried to replace 3 100nF which where linked to the 1st HEF4066BP -> No change

I went on ebay I I have purchased 4 Ics : 74LS05, 74LS04, and both HEF4066BP.

To gain some time, I have decided to unsolder them and put some sockets.
Then the idea was to invert the 2 HEF4066BP (I thought that maybe not all the switches on the 1st HEF4066BP were used).

Once I put back the 4 ICs, I give a try and the Coleco was working perfectly.

Here is a video : http://dl.dropbox.co...oleco/Final.MOV

And what look like my board :

I'm going to invert the 2 HEF4066BP to validate that the issue was here and do a conclusion.

[gibs]

SUCCESS !!!!!!!!

I'm happy to inform you that I have successfully fixed the Colecovision.

So...What I've done...

First I tried to replace 3 100nF which where linked to the 1st HEF4066BP -> No change

I went on ebay I I have purchased 4 Ics : 74LS05, 74LS04, and both HEF4066BP.

To gain some time, I have decided to unsolder them and put some sockets.
Then the idea was to invert the 2 HEF4066BP (I thought that maybe not all the switches on the 1st HEF4066BP were used).

Once I put back the 4 ICs, I give a try and the Coleco was working perfectly.

Here is a video : http://dl.dropbox.co...oleco/Final.MOV

And what look like my board :
All 10uF cap and 1uF have been replaced, 3 100nF on the left have been replaced. the DRAM comes from my ZX Spectrum.

I'm going to invert the 2 HEF4066BP to validate that the issue was here and do a conclusion.