The famous grey screen black frame issue.

[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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

[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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this.

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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Noel's video's are good and he gives lots of tips. One idea, worth looking at IC112. This is a simple 7432 quad 2 input OR but it plays a role in the memory and IO.

[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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this.

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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Noel's video's are good and he gives lots of tips. One idea, worth looking at IC112. This is a simple 7432 quad 2 input OR but it plays a role in the memory and IO.

Thanks!
After trying my oscilloscope for the first time, my VSync and clck on the z80 seems to be fine, working like your pictures. However, the M1 on the z80 seems to be dead 🤔 This could of course be due to my limited experience with the oscilloscope. Will investigate.

[Rabs]

As long as the VSync is at 50Hz, then I suspect it is being initialized by the lower ROM. When I removed the ROM it was only 20Hz. There is some debate on whether any VSync would be generated if not initialized but guess it may depend on the type of CRTC, mine was type 2.

I did not show you this previously but when I removed one of the multiplexers, on one occasion, I got this screen. This looks like one you posted but yours was green.

You cannot view this attachment.

[oyshals]

As long as the VSync is at 50Hz, then I suspect it is being initialized by the lower ROM. When I removed the ROM it was only 20Hz. There is some debate on whether any VSync would be generated if not initialized but guess it may depend on the type of CRTC, mine was type 2.

I did not show you this previously but when I removed one of the multiplexers, on one occasion, I got this screen. This looks like one you posted but yours was green.

You cannot view this attachment.

Thanks! At last I found a signal at the M1 on my Z80, but it was only at 300mV, and didn't look at all like yours, so I'm guessing it's dead.

Might change back to my old Z80 now that I've replaced the MUX and RAM chips.

Haven't had the time to follow the troubleshooting video from Noel's Retrolab yet, hoping to do that today.

[Rabs]

Could be just a bad contact with your probe. Make sure the pin is clean where you make contact. Or check some of the other signals like MREQ for activity.  Because if you are getting 50Hz on the VSync then I guess the Z80 is running and is reading the lower ROM.

[Bryce]

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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

As this seems to be your first scope, you should spend a few days testing known signals on another device to practice how to use a scope properly before you start making assumptions from bad readings / wrongly setup scope.

Bryce.

[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
Z80 CLK AND M1.jpg

VSNC
CRTC PIN 40 VSYNC ROM.jpg

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

CRTC PIN 40 VSYNC NO ROM.jpg

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.

20230317_180338.jpg

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.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

As this seems to be your first scope, you should spend a few days testing known signals on another device to practice how to use a scope properly before you start making assumptions from bad readings / wrongly setup scope.

Bryce

Yes, i noticed that, been over 20 years since last time I used one 😊

[oyshals]

Yesterday, I put back my old Z80 and Gate Array. Now I seem to have all the signals I need, including the M1, following Noel's video. My old Z80 doesn't get as hot as the new one I bought, so I think I might have gotten a bad Z80. The startup is also more stable, no black screen, only the old grey square and black frame.

The hottest components are now the PAL and the CRTC. Almost like they are working overtime.

Noticed that when i touched the video contact for the screen, the grey square turned yellow, so will continue reflowing solderings.

Also checked all tracks between RAM/PAL/MUX/GA/Z80, will continue with this.

Will also try to install Noel's diagnostics on the Dandanator as the one installed won't initialize, still black screen.

[Bryce]

This would be a good time to now check all data and address lines from the ROMs for shorts to GND or VCC (while the computer is disconnected from the power).

Bryce.

[oyshals]

This would be a good time to now check all data and address lines from the ROMs for shorts to GND or VCC (while the computer is disconnected from the power).

Bryce.

I think you were right, this might have been a good time to check that.

I found shorts between following pins:

40015: pin 1, 14 (gnd), 27, 28 (vcc) (all together)

40025: pin 14 (gnd) and 28 (vcc)

When noticing this, I measured a couple of other chips, 5v to gnd, and they were also shorted.

It gets more interesting: I disconnected the "aux" contact for the screen, and measured short between pin 28 (vcc), 27 and 1 on the 40015. Everything on 40025 was ok.

The first time i measured a couple of weeks ago, the screen was not connected, so guess I got a bit confused.

Edit: After looking at the diagram including the 40015, it seems that pin 1, 27 and 28 are all connected to 5v. So no progress.

[oyshals]

After finding no shorts in the ROM chips, I decided to give the Dandanator another try. Sadly it looks like the Dandanator depends on you being able to boot it on the Amstrad even to load the diganostics into it from the PC. But something on my CPC seems to be "blocking" it from initializing rendering it pretty useless at the moment.

Just to provoke a reaction from my CPC, I tried to remove the FAL, RAM chips, and MUX chips (one at the time). But sadly no reaction, still the framed grey screen.

Will keep reflowing solderings and measuring tracks, but I'm starting to think that the only solution will be replacing every IC one by one.

Sorry for all the updates, I know it may be annoying 😊

[eto]

If there is a short in one of the (ROM) chips, the Dandanator can't start as a data or address pin will always be high/low.

Instead of looking for pure shorts you could also check the resistance between a pin and VCC or GND. I once had the situation, that most pins had very high resistance (>100K) and one pin had (I think) around 400Ohms. When turned on the pin of the IC was not working correctly and was putting a constant high (or low) signal on the bus. As a result, nothing will work. Not the internal stuff and also no external add-on like the Dandanator. 

Btw: If you remove the ROM chips, you can try again with the Dandanator. If it was indeed a short in the ROM, diagnostics should finally boot as it doesn't need the internal ROM.

[oyshals]

If there is a short in one of the (ROM) chips, the Dandanator can't start as a data or address pin will always be high/low.

Instead of looking for pure shorts you could also check the resistance between a pin and VCC or GND. I once had the situation, that most pins had very high resistance (>100K) and one pin had (I think) around 400Ohms. When turned on the pin of the IC was not working correctly and was putting a constant high (or low) signal on the bus. As a result, nothing will work. Not the internal stuff and also no external add-on like the Dandanator.

Btw: If you remove the ROM chips, you can try again with the Dandanator. If it was indeed a short in the ROM, diagnostics should finally boot as it doesn't need the internal ROM.

Thanks!
I actually found something like that now, pin 22 only has 3,6k ohms to the vcc (pin 28) on the 40025 🤔 

Not sure if this is normal as it is connected  via r112 (2,2k ohms) to gnd according to the schematics. Resistance to gnd is correct. Measured on my new 40025, an there was "infinite" resistance. But again, the new one is not attached to a board...

Nothing found on 40015 for now.

[Rabs]

Think pin 22 (OE) is pulled low via the 2.2k resistor. This is also connected to edge connector pin 43  (ŔOMDIS) and I guess is pulled high when the Dandanator replaces the Lower ROM with the Diag ROM.

If you need me to check any signals by way of comparison just let me know.

Is there anyway you can check continuity on the edge connector?

[oyshals]

Think pin 22 (OE) is pulled low via the 2.2k resistor. This is also connected to edge connector pin 43  (ŔOMDIS) and I guess is pulled high when the Dandanator replaces the Lower ROM with the Diag ROM.

If you need me to check any signals by way of comparison just let me know.

Is there anyway you can check continuity on the edge connector?

Thanks, I might take you up on that offer, but right now, I'm not sure which signals I should be looking for. After alot of studying and checking, both on the forum, videos and on the board itself, this doesn't seem to be a ram issue, and the z80, CRTC, fal, mux and gate array seems to working. Comparing to most of what I've been reading, everything seems ok, but still not working 🤔 I've also been unable to find any "unusual" shorts.
So now it's a bit difficult to say where to start.

Btw, you were correct on the pin 22, high with Dandanator connected, and low when not.

[Rabs]

I assume you have watched Noel's video.

Interesting that he suggests to test any ICs in a known working CPC.

Quick check with you, are these correct?
CLK OK
M1 OK
VSYNC OK
HSYNC ?

Do you have a speaker attached?
Do you hear a BEEP when the Dandanator runs the Diag ROM.

[oyshals]

The plan was actually to get another one anyway, because this one I'm planning to give back to my older brother as a Christmas present (a bit of childhood nostalgia as we got i from our dad over 30 years ago), but I think you are right, I'll have to go on eBay earlier than planned 😊

Those signals seemed correct according to his other videos, but in those videos, he only looked for "traffic", as in this one he shows me the signals more clearly, so I will check again.

I don't get any beep when connecting the Dandanator at the moment. With the two "normal" roms (for games), it gives the same framed grey screen, but when trying to initialize the diagnostic rom, the screen turnus black.

Thank you for this video, don't know why I haven't seen it yet. And thank you for your patience!

[oyshals]

If I could bother you to post a picture of the interrupt signal on the z80, I would be grateful.
I think mine is locked at low. And also maybe the hsync and VSync signals just to be sure. I think mine are correct, but just to be sure.

[Rabs]

If I could bother you to post a picture of the interrupt signal on the z80, I would be grateful.
I think mine is locked at low. And also maybe the hsync and VSync signals just to be sure. I think mine are correct, but just to be sure.

Measurements taken from a working 6128 with just the READY prompt displayed.

VSYNC CRTC PIN 40 50Hz
You cannot view this attachment.

HSYNC CRTC PIN 39 15.62KHz
You cannot view this attachment.

INT GA PIN 32 (Note Frequency varies and is slow between 75Hz and 300Hz and you can miss it unless you have the scope setup to catch it, should be high most of the time). Note also this is connected to R144, which is connected to INT Z80 PIN 16.
You cannot view this attachment.

[Rabs]

What board revision do you have? Mine is an MC0020F. If you have one of these the schematic in the manual is different. But see this great bit of work by @pelrun CPC6128 - new schematic capture and layout for MC0020x boards.

[Rabs]

Have you watched this?

[oyshals]

Have you watched this?

Thanks, I will check the revision when I get the time.

Think I've seen it at a time I thought it wasn't relevant, will watch again.

If someone could provide me with the current draw (amps) of a working 6128 it would be very much appreciated. I've just based my thoughts on this
on something Noel said in a video, so confirmation would be great!

[Rabs]

Think the video from Noel covers a lot of what you may be seeing.

[oyshals]

Yes, that video was actually great! Will also make a 10th attempt at cleaning the edge socket 🙈