Games with CNG SOFT trainer fail to load in my CPC6128

[jeronmus]

Hello, I am relatively new CPC user. Bought my 1st CPC6128 last summer and been in love with it ever since.


I found out strange problem last week. Any DSK game that I have been trying to load (with M4 Board or from Gotek) fail to load as soon as CNG SOFT logo comes to screen after typical trainer questions. The logo starts to roll vertically out of screen and back from bottom for a few seconds after screen goes dark and nothing happens however long I wait.

Here's a link for a short video about the problem.

I've been trying to use games from collections mentioned in this CPCWiki thread, for example the Bomb Jack at http://cngsoft.no-ip.org/cpc_lzx.htm fails just like in the video. As does any other game that has CNG SOFT loader. The same Bomb Jack DSK plays just fine with WinAPE with CPC6128 mode. Any other games load and play just fine with my real CPC.

CNG SOFT games I've been trying to load are from 80's before Plus models were introduced, so it seems unlikely that the problematic games would be meant to play with Plus models. There's no modifications in my CPC6128 other than the floppy drive has been replaced with Gotek FF which seems to work just fine (except with CNG SOFT loaders).

What would cause the problem? Anyone else had the same?

[jeronmus]

I just downloaded a couple of different dsk-files with Bomb Jack. Both load perfectly and run nicely with M4 Board, so the game itself is not incompatible, only the trainer loader it seems.

I started taking notes which ones has the CNG trainer and fail to load. So far my list is this, but I chose games quite randomly:

   
• Krakout (UK)(1987).dsk
• Hunchback II - Quasimodos Revenge (UK) (1985).dsk
• Batman The Movie (UK) (1989) (Trainer).DSK
• Bomb Jack (UK) (1986) (Trainer).dsk
• Batman The Caped Crusader (UK) (1988) (Trainer).dsk
• Commando (UK) (1985) (Trainer).dsk Krakout (UK)(1987).dsk
  

No one else has problems with these? All these are either from Mr DVG's fine collection, CPC Compactages, CPCGamesCD or from Epidemiom M4-HFE v900 collection. Seems that these run nicely on WinAPE, but not on my real CPC6128. Each of these hangs right after CNG SOFT logo is loaded, just like on my video that I linked to original post.


Of course I can look for alternative versions of these dsk-files without trainer, but I'd like to to find out the cause of the problem.

[dragon]

Some type of incompatibility of cngsoft loader code with your hardware...


Its difficult to tell... I mean the only way if it works in emulators is trying put breakpoints in the code to try find where the code execution breaks.


Its not really a problem with the game, is  a problem with the code that decompress and load the game....


Anyway winape it's so relaxed with cpc rules. Try best arnold emu.

[robcfg]

@jeronmus , would you be so kind of taking pictures of your CPC's circuit board?


It would be interesting to check which chips (CRTC, Z80, AY, etc...) you have installed, because sometimes chips by different manufacturers can have slight ways of working.

[VincentGR]

I think this screen is overscan right?
Maybe is your crtc type.

[dragon]

Crtc type 2 fails in arnold emu with bomb jack. Not esactly same effect. Only blue screen but fails.

[jeronmus]

@jeronmus , would you be so kind of taking pictures of your CPC's circuit board?

It would be interesting to check which chips (CRTC, Z80, AY, etc...) you have installed, because sometimes chips by different manufacturers can have slight ways of working.

Here's a photo that I took when I got the machine and dusted it. Is it clear enough to identify the chips?
https://photos.app.goo.gl/rXV3X2rm5z14nkXbA

[dragon]

Here's a photo that I took when I got the machine and dusted it. Is it clear enough to identify the chips?
https://photos.app.goo.gl/rXV3X2rm5z14nkXbA

It have a Motorola mc6845p


Its a crtc2 that's the problem.


These crtc 2 have many problems with demos that's use tricks with it to create the screen effects as the cngsoft do in the loader.

[jeronmus]

It have a Motorola mc6845p


Its a crtc2 that's the problem.

Thanks for a swift diagnose!! Does that mean that my Motorola mc6845p chip is faulty or that it is working as intended, but just incompatible with those screen effects?

Can this be "repaired" by changing the CRTC2? If so, what would be a good and realistically available replacement chip?

Maybe regular old 80's games work fine with this, but certain hacktros and demos etc. that use certain tricks are not compatible.

[dragon]

Not it's not faulty. It's incompatible with many crtc tricks. That's all.


Yes you can change it if you know solder/unsolder. If you put a socket you can put any another crtc type.


The best are type 1 um6845R.

Part number Manufacturer Type number (note 3)

HD6845S Hitachi 0

UM6845 UMC 0

UM6845R UMC 1

MC6845 Motorola 2

AMS40489 Amstrad 3 (note 1)

40226 Amstrad 4 (note 2)

http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/what's-'wrong'-with-crtc-2/

Crtcs are common chips easy to find. In ebay for example only search UM6845R

[jeronmus]

Thanks so much for all the information!


I would have not found the connection of my problem and CRTC without all the help.


Now I just have to decide if I want really "authentic" experience with "original chip" and live with it.

So far there's only those hactros/loaders that wont work and I've managed to find compatible versions of those games that failed loading with my Motorola, so maybe not worth to buy a soldering job from someone. (I am not able to do this kind of PCB soldering myself).

Now I can sleep with ease, knowing that my CPC6128 is not seriously sick, it just has some imperfections as we all do. 

[dragon]

Or you can buy another cpc with 0 or 1. .

[ajcasado]

I have the same issue. My CPC664 has a CRTC2. You can run CNGSOFT cracked games with this crtc

patching the loader with pokes:

    -Using winape load the .bas with the basic command LOAD"NAME.BAS".

    -Once loaded push F7 to open the debugger and search for the string "ld bc,#bc06" in assembler (without quotes).

    -Take note of the search match memory addresss (e.g &5c92), take note of the next address after the following RET instruction after the address noted before (e.g. &5c9b).

    -For running the game in your amstrad with CRTC 2 load the game with LOAD"NAME.BAS" and execute POKE (first address),&C9 (e.g. POKE &5c92,&c9) and POKE (second address),&c9 (e.g. POKE &5c9b,&c9) then execute RUN.

The addresses used as example are used for the game abu simbel. The CNGSOFT logo will appear scrambled, but the game will run.

For the game abadia del crimen the pokes are POKE &7a5f,&c9 and POKE &7a68,&c9.

This trick bypass the loader manipulation of the crtc registers placing RET's (opcode &c9) in the loader code before the manipulation is done.

I attach captures of the debug window in winape for abu simbel.
To make this modification permanent you can edit the dsk in a PC with an hex editor and search for the hex pattern 01 06 BC ED 49 04 ED 71 C9 ED and change it with C9 XX XX XX XX XX XX XX XX C9 where XX means anything (eg. 00).