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CPC 6128 - white screen, black border

Started by mmldrm, 22:02, 31 March 24

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McArti0

#250
..
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

McArti0

Quote from: mmldrm on 10:45, 21 June 24Yesterday he replaced the lower 64Kb of RAM and... still the same white screen and black border.

(Thanks again for all time spent helping me here...)
The crystal divination ball for CPC duck diagnostics did not work. ???
Btw. If you don't have time, we won't anything.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

eto

Quote from: mmldrm on 10:45, 21 June 24Yesterday he replaced the lower 64Kb of RAM and... still the same white screen and black border.
Just to be sure: he replaced the right column of RAM ICs, right? (When I did my first repair I thought the left column is lower RAM.)

Were the RAM ICs fast enough and properly tested? 

Even if he is experienced he still might have caused physical harm, which can have the exact same symptom as a defect RAM IC. Did you already check for broken traces / removed pads? 


Quote from: mmldrm on 10:45, 21 June 24Dandanator? More experiments? Or the recycle bin.

What Dandanator would give you is the information which data line gives the wrong data. Based on that you can usually identify the defective RAM IC but it could also be that one of the other ICs related to the RAM circuit is defective. If you see all ICs in red then usually a different IC is the culprit. You might consider that while doing those massive tests you might have fried another IC accidentally. Or it was another IC from the start.

And please definitely not the recycle bin.  This one will be saved with max. 2h of work and max 20€ for parts (worst case scenario) if followed the "usual" repair steps. Where are you located? Maybe someone is willing to do the repair for you if you cover the costs for parts and shipping? Or before you throw it away send it to someone who pays for shipping and will fix it.

Bryce

Even if he did swap the wrong bank of RAM, you could now try the PAL jumper trick to see if the swapped bank works.

Bryce.

eto

Quote from: McArti0 on 11:41, 21 June 24The crystal divination ball for CPC duck diagnostics did not work. ???
Instead of crystal ball it was rather experience based recommendations.

And the most problematic part here is, that after all those snake oil tests you recommended, it could also be that an accidental and unrecognized short has fried another IC. So maybe (just maybe) replacing the RAM first would have fixed it - but now it has been worsened. We will never know.

abalore

If you are willing to pay the shipping to Spain and back, I can fix it for you.

McArti0

Quote from: eto on 11:09, 22 June 24
Quote from: McArti0 on 11:41, 21 June 24The crystal divination ball for CPC duck diagnostics did not work. ???
So maybe (just maybe) (...) but now it has been worsened. We will never know.
Next crystal divinaton ball too :laugh:

Unfortunately, I won't make anyone think.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

mmldrm

Quote from: abalore on 11:13, 22 June 24If you are willing to pay the shipping to Spain and back, I can fix it for you.
I will offer this option to my friend who owns the CPC, although I imagine the costs will be more than he wishes to pay (after buying the RAM and paying for the soldering).

Either way, thank you. 😊

mmldrm

I also noticed this on startup once or twice. After this, it boots to the usual white screen with black border. (The soldering guy thought it was not white but cyan after accidentally leaving on for many hours, but it still looks white to me.)

Not sure if these videos (particularly the blue lines) show progress, or regression. 😕

Anyway, I'm away for the next couple of weeks, so this is the last update for a while.

When I get back I'll do my best to check the RAM pins and maybe finally learn how to read the schematic diagram for traces and start that long process. The soldering guy said he checked all the RAM after installation, but it's still good to check it myself.

McArti0

#259
This is a regression. Connect +5v to RAMDIS and turn on CPC.
Ps. Don't listen to anyone here who scares you And fortune tellers

Did you get back the memory that was removed from CPC?

Ps2. Bright Cyan is color with all bit Hi like
OUT &7FFF,0 : OUT &7FFF, &40+&x11111
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

Gryzor

Ahhh yes nothing like joining a twenty year old community and calling some of the most respected and well known members 'fortune tellers'. You get 10 brownie points. 

McArti0

I lived behind the Iron Curtain where you died for the truth.  Reliability of information was a highly valued good, regardless of who said it and when.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

McArti0

@mmldrm

You need to check whether all legs 40030/31 have a good connection to the socket. But now I would go back to the wire connection of the PAL IC.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

abalore

Quote from: McArti0 on 13:23, 22 June 24I lived behind the Iron Curtain where you died for the truth.  Reliability of information was a highly valued good, regardless of who said it and when.
If information is valued regardless of who said, the place where you lived is just an argumentum ab auctoritate fallace.

McArti0

#264
For now, the information is that mmldrm was persuaded to desolder the memory by a random person and it is unknown whether with the GA removed.

The effects can be seen in the video. CRTC is no longer set correctly. Which was to be expected.
 
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

mmldrm

For better or for worse... I'm back. Apologies to anyone who groaned upon reading that.  ;D

To summarise, I got Bank 0 of the RAM replaced but it hasn't changed anything. There was a regression to a bad CRTC signal, but thankfully that is happening less and less. Occasionally on startup the video signal is out of sync, but given a few seconds and a couple of restarts, it does get back to the familiar grey box and black border. This is true with the 40031 and also with the "wire trick".

Looking for things to try, I saw Noel's video* on PCB tracks and tried tracing a signal from IC108 data bus pins (26-33), through the RAM chips, and then traced through to the Z80 data pins.

It was a great demonstration on how to trace signals and how to read the 6128 circuit diagram. However, all of traces from IC108 data pin to Z80 pins were fine.

Am I correct in thinking that the upper (Bank 1) RAM cannot affect the boot process? Because I'm wondering if there is an issue with that RAM.

Happy to do more traces, or any other suggestions, but I wonder if I am better off getting a diagnostic ROM installed.

Also, I do still have the original RAM.

Thanks again for all time/thought/experiments spent on this.

*

McArti0

#266
OMG! You are alive. :D

@mmldrm
"Am I correct in thinking that the upper (Bank 1) RAM cannot affect the boot process? Because I'm wondering if there is an issue with that RAM"

Anything is possible. Something might try to work then heat up and stop.

When cas1 is always Hi then ram bank 1 should not work.

ps. remove all RAM chips (don't confuse with old),  wire PAL for second bank RAM try do this procedure...
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

mmldrm

#267
So, I'm back again. I've been dabbling in the background but wanted to retry several things before returning here...

Sorry @McArti0, I still can't figure out how to follow your YouTube video. :( It is impressive that you can step through the instructions that way, but I am more likely to misunderstand something and get bad results or, worse, cause damage.

I've been going over the previous messages in this topic, now that I have a slightly better understanding of the CPC and general electronics, and have a few questions:

  • Touching/wiggling capacitor at C309 causes audio crackling. Others don't. Probably irrelevant but thought I'd mention it. Is that normal?
  • Leaving the 6128 running for a while, only the AY chip seems to get warmer than others. Not very warm, but warmer than the others. Is that a sign that the AY chip may have issues? Or would it have to be HOT to be a symptom of a bad chip?
  • 40025 ROM data lines are not stuck anywhere near 0V or 5V, but most values are unchanging and don't fluctuate over time. Does ROM code halt when it displays the black/grey screen? I would have expected to see voltage fluctuations if 'random' binary data was being processed.
  • 40010 voltages are nothing like what is expected in the table at https://www.cpcwiki.eu/forum/index.php?msg=237132 - again, is this simply because the boot process has not completed? Or maybe a sign of bad chip/chips?
  • How best to check IC pin signals? Oscilloscope (50Hz) with dual channels, comparing signals at different points?
  • Would it be better to spend £45 on a Dandanator or £60 on an oscilloscope (Zoyi ZT-703S)? Oscilloscope might be useful in the future. Dandanator will probably need to be resold, but if it is likely to give clear indications of chip failures then it seems worth trying first.

Apologies for some of those being general electronics questions (chip temperature, checking signals). I have also been watching many of Noel's videos (and others) trying to get a better understanding before writing this.

Thanks
M

McArti0

#268
1) This is the input of the audio amplifier. Normal.

2) A bit of fortune-telling. If something burned, the matter would be obvious.

3) You see the average value from one fast loop of the program. The values should be funny and constant.

4) These should be close, let's say with an accuracy of +/- 0.3V.

          GA 40010 GA 40007
------------------------------------------------
CCLK  ~1.2V  pin4      pin40
RAS   ~0.9V  pin34     pin7
nCPU  ~2.5V  pin14     pin1
PHI   ~2.1V  pin19     pin39
READY   ~1V  pin22     pin2



5) It's best to check wisely :D
1MHz signals are useful, i.e. READY, nCPU, etc. For example, on one channel READY, on the other nCAS.
details after studying the page:
https://bread80.com/2021/06/03/understanding-the-amstrad-cpc-video-ram-and-gate-array-subsystem/

6) A better oscilloscope is DPOX180H. If Dandanator does not show you an image or hangs, we will continue without tools like an oscilloscope.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

mmldrm

Quote from: McArti0 on 16:58, 08 December 246) A better oscilloscope is DPOX180H. If Dandanator does not show you an image or hangs, we will continue without tools like an oscilloscope.
I finally cracked and bought the DPOX180H. I was ready to get the Zoyi ZT-703S, but managed to find the DPOX180H for only £15 more. It's Christmas, and I didn't need anything else. Maybe I can get into retro electronics more in the future...

Thanks for the other answers. The scope should arrive just after Christmas. I will probably still do the above tests, but hopefully the scope will give more clues soon. :)

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