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hyuma

Trying to fix Colecovision PAL rev. D

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There is a NTSC rev D and a PAL rev D, and the revs have nothing to do with each other.  But if you've disconnected -5V and -12V from the video memory and added +5V where needed, then you should be good.
Yeah, 12v and -5v are disappeared, now I will order ram kit!

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Today for fun I desoldered the BIOS and read the content to check all was in place. It was a really cool thing to do! 5471973c6a542b017ab9646e68251ca1.jpg2f05457128a2f6729e9c11dfbbc67d6b.jpg

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if you cant get anything useful out of this thing after replacing the video ram chips i have had trouble personally with the following components

 

the two main ram chips      after deciding to replace all the chips on the board because they were cheaper then the two ram chips, it turned out to be the ram chips or chip i think it was that was dead, not everything else 🤦‍♂️

the clock crystal on a ntsc board (one pin had broken so it was only attached with one.  getting a replacement for that was an issue due to overpriced ebay shipping, had to get someone in the US to get it and send it to me so i could get it at a reasonable price.

 

 

 

i still have an issue with my French RGB board (which is the one the ram chips were dead on) where it displays faint white vertical bars on the screen,  i have replaced most of the video circuitry with new but it is stll doing it.   most annoying,  apart from that the machine turns on and functions.  its not the vdp as swapping it into another pal board and testing the board it was swapped into the video is fine, so i have been stumped on that one for some time unfortunatley

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Posted (edited)

the switch is a known bad component, especially after 30 odd years being sat around.  good practice is remove it, disassemble and make the internals shiny again with your preferred method, i use brasso then polish off

 

apply dielectric grease and reassemble and solder back in failing that replace with a different switch

 

 

Edited by omf
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Yeah i polished the switch too
Today I tested other sets of ICs, U30, U31, U32, U18, U19 and all are fine. I have ordered a set of 4164 then let's see next week if the issue disappear! 259f5aa8ce6ab9e2eba1abeb578df1f7.jpg

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if you cant get anything useful out of this thing after replacing the video ram chips i have had trouble personally with the following components
 
the two main ram chips      after deciding to replace all the chips on the board because they were cheaper then the two ram chips, it turned out to be the ram chips or chip i think it was that was dead, not everything else


If you meant the RAM chip 2114 U3 and U4 I tested with arduino code and they are ok



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Ok, RAM replaced, 4164 socketed, black screen with some lines on black screen but I can see PAL message on CEC. I have to test with some CRT and try some composite mod...

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Ok, with composite mod on breadboard i got on my LED TV the message "PAL"  that appears on the top right of my TV. That should be the CEC. After a bit the message doens't worked anymore so i'm assuming that the VDP is not working well. When i wil receive my oscilloscope I will check the signals on it, and for now i just bought a new TMS9929ANL. 

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On 3/11/2021 at 3:48 PM, hyuma said:

Ok, RAM replaced, 4164 socketed, black screen with some lines on black screen but I can see PAL message on CEC. I have to test with some CRT and try some composite mod...

That means your system clock works, as does the 10MHz resonator, and the 9929 is generating a picture.

 

You should check the 74LS138's and the 74LS04 next.  With everything else checked, if you still get nothing, then the Z80 could be the problem.

 

You could also wire up your composite mod directly to the Y output of the 9929 to see if you at least get a B/W output.

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That means your system clock works, as does the 10MHz resonator, and the 9929 is generating a picture.
 
You should check the 74LS138's and the 74LS04 next.  With everything else checked, if you still get nothing, then the Z80 could be the problem.
 
You could also wire up your composite mod directly to the Y output of the 9929 to see if you at least get a B/W output.
Yeah 74LS04 and 74LS138 tested and working good. I've used the TL866IIplus programmer.

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How many channels does your logic analyzer have?  You could hook them up to the data lines of the CPU to see if it's alive.

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How many channels does your logic analyzer have?  You could hook them up to the data lines of the CPU to see if it's alive.
It have 16 channels, Data lines on z80 are pins 7,8,9,10,12,13,14,15? 786cc0683e9a7e4c0c035faa9a4817e1.gif

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9 minutes ago, hyuma said:

It have 16 channels, Data lines on z80 are pins 7,8,9,10,12,13,14,15? 786cc0683e9a7e4c0c035faa9a4817e1.gif

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Yep.  And address lines on A0-A15.

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Yep.  And address lines on A0-A15.
Ok, I'll check both and I post results

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Posted (edited)

@ChildOfCv

 

I recorded two videos: one is Data lines and the other ones is Address lines of Z80. Next monday I will receive the oscillope that i bought and maybe the signals will be more clear.

 

Edited by hyuma

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I see a lot of dead lines in those analyses.  It strongly suggests that the CPU is dead.  At least A0,A1 ought to be doing something, since execution of instructions requires a lot of sequential reads.

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7 minutes ago, ChildOfCv said:

I see a lot of dead lines in those analyses.  It strongly suggests that the CPU is dead.  At least A0,A1 ought to be doing something, since execution of instructions requires a lot of sequential reads.

I have a Z80 from a Sega Mega Drive that I know is working that I will use as replacement there ;)

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Oscilloscope arrived, Z80 seems really have serious issue, ordered a new one, waiting it for arrive ;)

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@ChildOfCv New zilog in place but I noticed that the clock is different... Maybe I made a mistake buying the zilog?? aa9ea0dfef4be817116b30f2a81ba975.jpg

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Do you mean that your replacement can't handle the speed?  TIL, the original Z80 had a 2MHz limit.  The Z80A can clock up to 4MHz, and the Z80B can clock up to 6MHz, and so on.

 

Also note that pin-compatible clones exist.  My CV has a NEC μPD780C-1.  (note that the -1 is important in this case)  Looks like you have the SGS-Thompson version.

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Posted (edited)

@ChildOfCvI just notice that i bought Z80 PIO and not Z80 CPU, check the image, there is written Z80 PIO on the chip... I didn't read well the ebay acution... now i found a seller here near my city that have Z80 but it's 8MHz.. is this a problem? Should i have to use a strict 4mhz cpu? thanks!

Edited by hyuma

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Posted (edited)
1 hour ago, hyuma said:

@ChildOfCvI just notice that i bought Z80 PIO and not Z80 CPU, check the image, there is written Z80 PIO on the chip... I didn't read well the ebay acution... now i found a seller here near my city that have Z80 but it's 8MHz.. is this a problem? Should i have to use a strict 4mhz cpu? thanks!

8MHz can run at slower speeds (even 0 ;) ) so that shouldn't be an issue.  If you can find the full part number, the datasheet will tell you if there's a minimum speed.  But when Z80 went to CMOS, they eliminated the minimum speed.

 

Looks like Jameco has the actual CPU you need in stock though.  https://www.jameco.com/z/Z80A-CPU-Major-Brands-IC-Z80A-4-8-16bit-CPU-N-Channel-Silicon-Gate_35596.html?CID=MERCH

Edited by ChildOfCv

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Ok, New cpu Z80 in place, address line now are good with activities and not stuck hi or low as before. Composite mod in place but still black screen and some green lines or dot sometimes with PAL message top right of TV that appears when I turn on the console. As I have ordered a new tms9929anl and waiting for it that arrives, just for study I should check in the old one pin 35-36 and 38?

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