The famous grey screen black frame issue.

[JupiterJones]

I don't have a Dandator or know about its inner workings, so I can't comment on that. Regarding the RAM, it's not as some may assume, ie: 8 chips with 8k bytes per chip. Each chip stores just 1bit of each of the 64k of bytes. So if just one RAM chip fails, the entire 64k bank has failed.

Regarding scopes: 5MHz is completely pointless for most things other than analogue audio work. The bandwidth should ideally be around 5x the highest frequency you intend to measure. So for the CPC 5x16 = 80MHz, but you can get away with a 50Mhz scope for most retro related work.

Bryce.

If you have the chance, Noel explains in this video some inner insight of the diagnostics ROM, besides solving an issue with the disk drive. Maybe that would help: 
https://www.youtube.com/watch?v=tw0ClciNUDQ

[Rabs]

I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
You cannot view this attachment.

VSNC 
You cannot view this attachment.

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

You cannot view this attachment.

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

You cannot view this attachment.

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

[oyshals]

I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
You cannot view this attachment.

VSNC
You cannot view this attachment.

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

You cannot view this attachment.

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

You cannot view this attachment.

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Thank you very much! I will order an oscilloscope on my next paycheck, looks like a long term project 😊 Think I will start measuring traces meanwhile! I guess changing all ram chips would be a waste without more troubleshooting first!

However, after replacing the power supply socket, I still loose a lot of voltage when connecting the Dandanator, approx 0,2v, so I probably have one or more defective IC, guess I'll need the oscilloscope to locate it.

[Rabs]

Checking traces is not a bad idea. You may find a faulty track, you never know. I had several on my 664 but the  PCB was in a bad way.

[oyshals]

Thanks @Rabs My board appears in good condition but i have read in another thread that damaged traces aren't always visible so no harm in checking.

"Nice" to see a familiar screen, this gives me hope that it's fixable, I think your pictures will help a lot once I get the oscilloscope. The sad thing is shipping time these days😫

BTW, sometimes, it sometimes starts with a yellow or pixeled screen, still with the frame, but I'm pretty sure this comes from me touching/moving the board while working on it.

Your post gave me the urge to recheck everything, so I started with the thermal camera. The Z80 with 60 degrees Celsius, the CRTC with 50 and the fal with 45 degrees stands out, so whatever is wrong is probably causing these chips to work harder. Also noted that all 16 ram chips measures an even 30 degrees, an my 4 MUX chips is barely over room temperature, approx 20 degrees.
The z80 and fal chip are new, and shows the same as the old ones, so my guess is that they are ok. Have a new CRTC, but will wait until I know more before replacing.
@WacKEDmaN also suggested MUX earlier, so I will track down some new ones.

I also checked the clock signals, and followed their traces. Seems to be good. I know that I need an oscilloscope to be sure, but for "fun", I checked the VSync fro the CRTC, and it shows 50hz.

I should probably take a break and clear my head while waiting for proper equipment, but I guess I'll keep tinkering.

I'm really impressed with the effort you people put in to help others, so again, thank you very much!

Edit: When starting with the Dandanator in diagnostics mode (holding left button) I seem to loose the 16Mhz clock on the GA, in addition to the voltage dropping by 0,2v. That would explain the screen turning black/dark grey... I think something is using a lot of power...

[Rabs]

In the interest of science and because I wanted to find out, I removed one RAM IC and got the same grey screen black border. So either a multiplexer failure or single RAM IC can give the grey screen.

I also repeated the tests with the Diagnostics ROM. Note, I replaced the lower ROM on the PCB of my 664,  as I do not have a Dandanator.

So with one RAM IC removed I get this.

You cannot view this attachment.

And with one multiplexer remove, I get this.

You cannot view this attachment.

So I do not know why your Dandanator is not working.

I guess that if you have a grey screen the Gate Array is running, the Z80 is running and reading the ROM  to setup the CRTC, which is also running. If any one of these was not running the screen would be black.

Hope this helps.

[oyshals]

Thanks, think that'll be helpful! Just ordered 4 MUX chips from icompplus.

Next step will be re-learning how to use the oscilloscope when it arrives, before I start desoldering.

Has anyone experienced any problems with the 5v power supply on the monitor due to old age?

[Rabs]

I tend to use a bench power supply when testing, just in case. So sorry can't comment on the CRT. But the 664 I restored did exhibit a grey screen also but this turned out to be a bad joint on the power header pins (oddly not the power connector). Reflowed the pins on the header and this solved the problem. Guess one symptom can have many root causes  .

[oyshals]

I tend to use a bench power supply when testing, just in case. So sorry can't comment on the CRT. But the 664 I restored did exhibit a grey screen also but this turned out to be a bad joint on the power header pins (oddly not the power connector). Reflowed the pins on the header and this solved the problem. Guess one symptom can have many root causes  .

That's what I've learned lately 😅 I will try to monitor the voltage as I flip the switch next time, to see if I have a drop as it tries to boot 👍

[oyshals]

Measured the current it draws from the power supply, came out at 1,08 amps, seems ok according to Noel's Retrolab.

[oyshals]

Tested with new power supply, same result, will leave it now until I recieve my oscilloscope. Getting frustrated, but not giving up.

[Rabs]

I still don't understand why the Lower Diagnostics ROM is not asserting on your Dandanator. The fact that you get a grey screen still implies to me that the standard Lower ROM on the CPC is still running. Also the fact that you get a grey screen and not a black screen implies to me that the Z80 is running, reading the Lower ROM, initializing the CRTC and hence the GA is running. I know you have cleaned the edge connector but I have had spurious faults with one of my CPCs and even now sometimes the ROMs do not assert and I have to re-attached the ROM Board. I found it difficult (not conclusive) to just check the PCB edge connector continuity and in the end used an actual edge connector and checked from there (i.e. checked what the connecting board would see).

[oyshals]

I still don't understand why the Lower Diagnostics ROM is not asserting on your Dandanator. The fact that you get a grey screen still implies to me that the standard Lower ROM on the CPC is still running. Also the fact that you get a grey screen and not a black screen implies to me that the Z80 is running, reading the Lower ROM, initializing the CRTC and hence the GA is running. I know you have cleaned the edge connector but I have had spurious faults with one of my CPCs and even now sometimes the ROMs do not assert and I have to re-attached the ROM Board. I found it difficult (not conclusive) to just check the PCB edge connector continuity and in the end used an actual edge connector and checked from there (i.e. checked what the connecting board would see).

I don't know if this is relevant, but actually when I try to activate the diagnostics rom on the Dandanator the screen turns black. (I think I wrote "dark grey" earlier, but it's close to black, and no frame.) Maybe something is wrong with my Dandanator?

Edit: My voltage also drops by 0,2V when activating the Dandanator.

[oyshals]

You cannot view this attachment.

Recently I've been getting more of this, in different colors, especially after replacing the 5v socket.
Especially when I haven't turned the CPC on for a while. This changes back to grey when touching or moving the board. I suspect some bad soldering when replacing the socket.

Look familiar to anyone?

[Rabs]

I still don't understand why the Lower Diagnostics ROM is not asserting on your Dandanator. The fact that you get a grey screen still implies to me that the standard Lower ROM on the CPC is still running. Also the fact that you get a grey screen and not a black screen implies to me that the Z80 is running, reading the Lower ROM, initializing the CRTC and hence the GA is running. I know you have cleaned the edge connector but I have had spurious faults with one of my CPCs and even now sometimes the ROMs do not assert and I have to re-attached the ROM Board. I found it difficult (not conclusive) to just check the PCB edge connector continuity and in the end used an actual edge connector and checked from there (i.e. checked what the connecting board would see).

I don't know if this is relevant, but actually when I try to activate the diagnostics rom on the Dandanator the screen turns black. (I think I wrote "dark grey" earlier, but it's close to black, and no frame.) Maybe something is wrong with my Dandanator?

Edit: My voltage also drops by 0,2V when activating the Dandanator.

You should hear a beep before the RAM test runs.

[Rabs]

You cannot view this attachment.

Recently I've been getting more of this, in different colors, especially after replacing the 5v socket.
Especially when I haven't turned the CPC on for a while. This changes back to grey when touching or moving the board. I suspect some bad soldering when replacing the socket.

Look familiar to anyone?

Sounds like you need to check traces and reflow connections.

[oyshals]

Screenshot_20230403-150824.png

Recently I've been getting more of this, in different colors, especially after replacing the 5v socket.
Especially when I haven't turned the CPC on for a while. This changes back to grey when touching or moving the board. I suspect some bad soldering when replacing the socket.

Look familiar to anyone?

Sounds like you need to check traces and reflow connections.

Started working on that today, also replaced two MUX chips with sockets and new chips, just to practice my soldering skills, not pretty, but seemed to work. Will buy a smaller soldering pen though 😅

[oyshals]

I can't seem to leave this alone while waiting for my oscilloscope 😅

I've reflowed most of the 5v connections, also replaced and socketed all four MUX chips.

Still having issues with the voltage (I think), 4,5 to 4,8v. If this was larger electric plant, I would suspect the warmest components, like the z80, FAL, gate array and CRTC for drawing to much current, or maybe most of my capacitators have dried out? (Z80, GA and FAL are brand new)

I think I will have a look at installing Noel's diagnostics on my Dandanator as I'am starting to suspect that the diagnostic tool is not there or something is wrong with it...

[oyshals]

I have more or less concluded that the diagnostics rom on my Dandanator is not working, as when I push the diagnostic button when starting, the screen turns blank/black/dark grey with no frame. After reading almost all relevant posts on the forum, this means I am not able to initialize that specific rom.

So yesterday I started desoldering chips on the right ram bank (bank 0). I have new sockets and chips, but seems like the easiest way due to spacing is to remove all of the chips.

Edit: Have been running the board with external power supply, and now have 5v all over, and 1amp. Guess the power supply from the monitor is a bit old and dodgy.

Desoldering one or two a day to not get tired and break something. So patience is key.

[Rabs]

I can't seem to leave this alone while waiting for my oscilloscope 😅

I've reflowed most of the 5v connections, also replaced and socketed all four MUX chips.

Still having issues with the voltage (I think), 4,5 to 4,8v. If this was larger electric plant, I would suspect the warmest components, like the z80, FAL, gate array and CRTC for drawing to much current, or maybe most of my capacitators have dried out? (Z80, GA and FAL are brand new)

I think I will have a look at installing Noel's diagnostics on my Dandanator as I'am starting to suspect that the diagnostic tool is not there or something is wrong with it...

I don't have a Dandanator, but have you seen Amstrad Noob's video on loading the diag ROM?

https://www.amstrad-noob.com/2021/03/10/video-loading-amstrad-diagnostics-on-a-dandanator/

[Bryce]

Did you ever check whether any internal ROM pins are shorted to GND or 5V? This is a common problem and would definitely stop the Dandator from working.

Bryce.

[oyshals]

@Rabs Have watched the video, but haven't installed Noel's diagnostics yet, as I find it strange that I can't even load the diagnostics rom.

However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Did some measurements as @Bryce suggested, with a multimeter, and there seems to be shortages between pin 14 and 28 and several other pins on my roms 40015 and 40025.

Edit: These shortages are only present when power is on, not when the computer is turned off.

[Bryce]

@Rabs Have watched the video, but haven't installed Noel's diagnostics yet, as I find it strange that I can't even load the diagnostics rom.

However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Did some measurements as @Bryce suggested, with a multimeter, and there seems to be shortages between pin 14 and 28 and several other pins on my roms 40015 and 40025.

Edit: These shortages are only present when power is on, not when the computer is turned off.

You can't measure a short when a circuit is powered.

Bryce.

[Rabs]

However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Oh dear. A black screen suggests to me the CRTC is not being setup by the lower ROM. When you say "more often", it sounds like an intermittent problem. Guess you will have to re-trace your steps and re-check some basics like clock signal etc. When I socket any ICs, I always continuity check tacks to make sure I have not damaged anything in the process.

[oyshals]

However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Oh dear. A black screen suggests to me the CRTC is not being setup by the lower ROM. When you say "more often", it sounds like an intermittent problem. Guess you will have to re-trace your steps and re-check some basics like clock signal etc. When I socket any ICs, I always continuity check tacks to make sure I have not damaged anything in the process.

Will do, also think I will receive my oscilloscope tomorrow 👍