Another faulty 6128, is it ram ?

Started by SkulleateR, 21:50, 21 November 19

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SkulleateR

Ok, after some weeks I turned on my 6128 again and started coding. After some time I thought about playing Pinball Dreams again, but all I get is a black screen after start, sometimes I get a light blue screen with some artifacts.


So I decided to test some other games, all 64k games run fine, 128k games don´t ... most of the time I get a black screen, oh btw. .. I´m using the M4 Board ...


Opened it up, and it seems (don´t got a heat meter here) IC127 to IC129 getting a bit hotter than the others.


Guess I have to change the upper 64k ? Or could it be something else here ?

llopis

It seems pretty likely it's the upper 64K RAM, yes.


One thing you can do is remove the PAL and hardwire the memory configuration to use the upper 64K as the lower ones. I don't have it handy, but if you search in the forum you'll find a long thread where this is explained in detail.

VincentGR

#2

- remove the PAL from its socket
   - on the socket :
      - link pin 9 to pin 19 (A14 to A14out) (Eq to LK5)
      - link pin 8 to pin 12 (A15 to A15out) (Eq to LK6)
      - link pin 7 to pin 16 (NCAS to NCAS1)
      - link pin 17 to pin 20 (NCAS0 to VCC)


(got it on a text file for backup  ;D )




http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/repairs-to-a-cpc6128/

Bryce

I have a "physical backup" too :)

Bryce.



llopis

Oh that's brilliant! I need to copy that  :)

Bryce

Feel free to download and print it :D

Byrce.

SkulleateR

Thx guys, will try the bankswitch at the weekend  8)

SkulleateR

Ok, didn´t come around to hardwire the thing, but I just found an old PC Ram card, think I can use these ?




Bryce


SkulleateR

Ok, found some time today, but before I get into rewire the thing I startet geralds RAMTEST on my M4 Board and everything seems ok, all is green ....


But no 128KB game starts, tried Pinball Dreams (crashes with light blue screen), Guild of thieves (just a black screen) and some others ...


HELP  :picard:  ?

gerald

Quote from: SkulleateR on 19:11, 28 November 19
Ok, found some time today, but before I get into rewire the thing I startet geralds RAMTEST on my M4 Board and everything seems ok, all is green ....


But no 128KB game starts, tried Pinball Dreams (crashes with light blue screen), Guild of thieves (just a black screen) and some others ...


HELP  :picard:  ?
You can have a go with this WIP version ?
After testing the main RAM, if the result is OK it will then run a test on the extension RAM.
The extension RAM is done in 2 pass, one with basic value, one with pseudo random value. The second pass is able to detect more failure mode.


SkulleateR

Thx for this  ;)


Ok, it stops right at 7F, see screenshot ... so is this start of bank 1 ?




gerald

Quote from: SkulleateR on 20:19, 28 November 19
Thx for this  ;)


Ok, it stops right at 7F, see screenshot ... so is this start of bank 1 ?
This is the full 64K extension, the test will check for up to 4MB. Then extension are the tested by 16K chunk.
So there is clearly an issue with your second bank. 
Unfortunately, this part of the test do not report bit level information, but if the ramtest passed with the pal removed and using the extension bank, that mean the fault is address related and not data related.
The only solution I would suggest is to change the 8 devices with know good ones and check that test pass.Then re-test putting back each suspect device one at a time.


VincentGR

Hey gerald, on which rom slot does this goes?

gerald

Quote from: VincentGR on 21:14, 28 November 19
Hey gerald, on which rom slot does this goes?
Lower ROM

VincentGR


Bryce

Quote from: gerald on 19:52, 28 November 19
You can have a go with this WIP version ?
After testing the main RAM, if the result is OK it will then run a test on the extension RAM.
The extension RAM is done in 2 pass, one with basic value, one with pseudo random value. The second pass is able to detect more failure mode.

Great new feature @gerald!

Bryce.

fgbrain


I think this mod is even better (make a switch to swap ram banks?)

http://www.cpcwiki.eu/index.php/File:Khany%27s_BankSwapper.jpg

havent test it myself yet but..
perhaps a hardware guru here can say more about it ???
_____

6128 (UK keyboard, Crtc type 0/2), 6128+ (UK keyboard), 3.5" and 5.25" drives, Reset switch and Digiblaster (selfmade), Inicron Romram box, Bryce Megaflash, SVideo & PS/2 mouse, , Magnum Lightgun, X-MEM, X4 Board, C4CPC, Multiface2 X4, RTC X4 and Gotek USB Floppy emulator.

TotO

What is the goal to hack the CPC to swap the RAM banks, while you can test and replace defective IC with a simple adapter and next repair or use an external RAM expansion?
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

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