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[Alphaone]

Hello I have a black screen. Pin 40 shows nothing on the CRTC Pin 39 has 3.91 khz. I've tested every IC on the board and they all have tested good. I have a good clock signal on pin 21. Looking at the schematic  it appears IC 110 pin 8 connects to pin 23 on the crtc . Should there be activity on that line? Mine shows nothing.

Thanks.

[McArti0]

15,625 / 3.9 khz = 4 (4 times slower)

Check whether there is a frequency on PIN34, PIN 35 CRTC (it should not be)

Maybe LowROM is setting the CRTC wrong?

Can you hear the sound at press DEL?

Check keyboard scan IC101 pin1-11 (need 50Hz) (before 5V and PIN)

What is the GA version?

[Rabs]

As @McArti0 indicated you won't get the required 15.62Khz HSYNC if the CRTC has not been programmed, so could be lower ROM.

I am guessing you have checked for Z80 activity (M1, WR and IORQ)?

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PIN 39 HYSNC 15.62KHz
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PIN 40 VSYNC 50Hz

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PIN 23 EN (you will only see activity if the z80 is running and issuing IN/OUT instructions).

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[Alphaone]

If I try putting the lower ROM from a 464 will the 6128 be able to boot? I've Swapped the Z80 already, and it tests fine in the 464. I've been able to test every IC on the board except the ROM IC's. I did try to boot off my dandanator which has Noels' diag rom on it though. No difference.

[McArti0]

IC103 is 32kB LowROM and BASIC. if all other chips are working then you can put on the ROM.

ps. where is AMSDOS? Who knows?
ps2. 40015 is AMSDOS and is not on schematic mainboard.

[Rabs]

IC103 is 32kB LowROM and BASIC. if all other chips are working then you can put on the ROM.

ps. where is AMSDOS? Who knows?
ps2. 40015 is AMSDOS and is not on schematic mainboard.

The disk controller circuit is on page 33/34 of the 6128 service manual.

[Alphaone]

So I've found that with the Rom removed and the Dandanator connected I can boot into the old RAM test. I press the left button when powering on, and it acts like it wants to boot into the new diagnostics I have installed on the dandanator. I get a blue screen with the square, but it then switches back to basic ram test. It's not always the same ram failing. It just says most of them are failing though.

[Rabs]

So I've found that with the Rom removed and the Dandanator connected I can boot into the old RAM test. I press the left button when powering on, and it acts like it wants to boot into the new diagnostics I have installed on the dandanator. I get a blue screen with the square, but it then switches back to basic ram test. It's not always the same ram failing. It just says most of them are failing though.

You should be able to boot the Lower Diagnostics ROM from the Dandanator when the Amstrad Lower ROM is in place by holding down the left button during power on. Initially you should see a red screen with a blue background and hear a beep as the lower RAM test runs. Something like this.

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When the RAM test completes you should hear another, lower, beep if the test fails and then the test output.

If you cannot boot the Lower Diagnostics ROM from the Dandanator with the Lower ROM in place then either the Lower ROM is corrupting the bus or it is not being disabled. The Lower ROM is disabled by pin 43 on the expansion bus.

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I would make sure the Expansion Bus edge connector is clean. I have had odd results when it is not clean (with one CPC I had to clean the edge connector several times before getting stable results). But I am not sure if this would also contribute to varying RAM ICs failing.

[Alphaone]

So I still can't get into the Lower Rom Diagnostics. I checked continuity and it was good. I however after fixing a short and adding 3 bodges can almost get a normal basic screen. Most of it is there but it is corrupted. So today I decided to compare signals from my working 464 to my broken 6128. The one major difference I found was on pin 22 write on the  z80.


The ready signal was 16 mhz to 1 mhz. I'm guessing that is the design differences.

[McArti0]

Pin 22 is the /WR signal. The processor has no write commands, and if there is no ROM, there are no commands.

[Alphaone]

I only have the Amsdos IC removed. is that needed for WR commands? Since I can almost see the basic screen isn't the Rom functioning? 

[Rabs]

I only have the Amsdos IC removed. is that needed for WR commands? Since I can almost see the basic screen isn't the Rom functioning?

Can you share an image of the screen?

[Alphaone]

[Alphaone]

I hear 3 soft beeps before the ram test fails.

I do get activity on pin 22 when the ram test is occuring. All the ram tests fine on my ram tester.

[Rabs]

I hear 3 soft beeps before the ram test fails.

I do get activity on pin 22 when the ram test is occuring. All the ram tests fine on my ram tester.

OK, so something is corrupting the bus. Have you run Dandanator Diag ROM with both the Lower ROM and AMSDOS ROM removed? If you have and you get the same results then the only other thing to place data on the bus is the disk controller IC201.

[McArti0]

i think ROM IC103 32kb crashes. Crashes font, crashes string.

is in dandanator dump memory soft?

[Alphaone]

Hey, Thanks.  Removing the FDC allowed me to boot into the Lower Rom Diagnostics!  Never would have thought this would be the cause of it. I tried another known working FDC and the problem reappeared. When I try to boot into normal basic without the FDC it appears normal but blinks. The screen doesn't blink in diags though. I'll have to check my traces around the FDC. Makes sense this would be the problem. The original 3 inch Floppy wasn't working So I wanted to put in a Gotek. Couldn't get it to read correctly, so I kept unsoldering and testing more and more IC's until nothing worked.

[Alphaone]

I found it was actually IC 203 causing the issue. Once I bent out pin 12 it booted to the Dandanator just fine. I didn't cause that so that sorta makes me happy I guess.

[Rabs]

I found it was actually IC 203 causing the issue. Once I bent out pin 12 it booted to the Dandanator just fine. I didn't cause that so that sorta makes me happy I guess.

Great, yes makes sense as pin 12 is associated with the FDC chip select logic. I have also encountered a faulty IC203 in the past but in that instance it prevented disks from being read.

[McArti0]

It was impossible to guess from a distance.