Grey screen of death (revisited)

[pabloingreece]

Good morning, I have a non working cpc6128 when I switch it on, the "grey screen of death" appears, I've replaced the ram because it was too hot, but still the screen is grey with black border.


I've noticed that the following ICs are hot (I ordered from too hot to not too hot):


1. HAL 16L9ACN IC
2. FDC 8627 IC
3. Z80 (not too hot, I put another Z80 chip again warm up like the old, not much)


The memories are no longer warm and have a normal temperature (cold).


If someone can guide me for the next steps ... thank you!

[Bryce]

The three chips you mention should get a bit hot when working normally. When you say "grey screen of death", does it have a border or is it all one colour? If it doesn't have a border, then there's a good chance that it'S the CRTC that's gone bad, but without further analysis it's difficult to be 100% sure.

Does the computer beep when you hold down the DEL button?

Bryce.

[pabloingreece]

Hi Bryce! The screen has a border 0 (black) with paper grey, and the keyboard when pressed does not make any sound or beep.


Any further information you need please let me know, I can measure voltages if needed.


Thanks!

[rpalmer]

Pabloingreece

You might also have a damaged VGA. This might not allow the ROMs to switch in and hence run code meaning the Z80 is just executing NOPs (data byte 0). The damage could have been heat related, but cant be sure.

Are there any other chips feeling hotter than expected? If there are then you may have short somewhere which is not allowing the system to work properly.
Check if the tracks are corroded with a magnifying glass such as those close together which may make contact through rust. Particularly check the expansion bus as these can become a problem.

rpalmer

[pabloingreece]

Please rpalmer, let me know how to check if VGA is damaged? do you mean the CRTC IC? Can I check if there is any short circuit by measuring pins?


Thanks!

[gerald]

If you can see a black border and grey screen the Z80, CRTC and the Gate Array are mostly OK.
To have this screen, the Z80 managed to read the ROM and configure the CTRC. If not you would only get a black screen.

However, it likely a RAM access problem.
In a 6128, you need the following to access the RAM :
- the PAL
- the Gate array (which does all the multiplexing
- the data buffers (IC114 / IC115)
- and ... the RAM

If you have a doubt on the PAL, you can remove it and close LK5/LK6 (above the PAL) and LK8 (at top of the main DRAM bank). This will put your 6128 into a 464 configuration. Since you have the RAM on socket, you better remove the second bank to be sure they will not interfere with the main one while their are not controlled anymore. The second bank is on the left side, away from the PAL
You can also test it in another 6128 if you have one.

If you have a XMEM or LowerROM board, you can also run my memory test : http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc

[rpalmer]

pabloingreece,

Its difficult if not impossible for hobbyists to check the VGA chip.

The fact you have a border, but no keyboard or sound made me think again that maybe the 8255 is damaged. This chip manages the acesss for sound and keyboard and if its damaged then neither is possible.

rpalmer

[Bryce]

What VGA are you talking about? A CPC doesn't have a VGA chip. Is your Auto-correction making a VGA from GA?

It's highly unlikely that the 8255 is the issue. If it was broken you'd still get as far as a prompt on the screen.

Bryce.

[pabloingreece]

If you can see a black border and grey screen the Z80, CRTC and the Gate Array are mostly OK.
To have this screen, the Z80 managed to read the ROM and configure the CTRC. If not you would only get a black screen.

However, it likely a RAM access problem.
In a 6128, you need the following to access the RAM :
- the PAL
- the Gate array (which does all the multiplexing
- the data buffers (IC114 / IC115)
- and ... the RAM

If you have a doubt on the PAL, you can remove it and close LK5/LK6 (above the PAL) and LK8 (at top of the main DRAM bank). This will put your 6128 into a 464 configuration. Since you have the RAM on socket, you better remove the second bank to be sure they will not interfere with the main one while their are not controlled anymore. The second bank is on the left side, away from the PAL
You can also test it in another 6128 if you have one.

If you have a XMEM or LowerROM board, you can also run my memory test : http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc

Hi, thanks for all this information!


So, I have another cpc6128, I can check the HAL... also I have a M4 Board that allows to use alternative ROMS (in fact, it can be set a lower-rom), but I don't have a RAM board, where can I I found one XMEM? Can I buy one easily?


I've tested the m4 board on the faulty cpc but the same result, black border and grey background.


Greetings!

[Patrick]

What VGA are you talking about? A CPC doesn't have a VGA chip. Is your Auto-correction making a VGA from GA?

Sometimes the GA is called VGA for Video Gate Array.

[gerald]

So, I have another cpc6128, I can check the HAL... also I have a M4 Board that allows to use alternative ROMS (in fact, it can be set a lower-rom), but I don't have a RAM board, where can I I found one XMEM? Can I buy one easily?

According to its documentation, it looks like the M4 can replace the lower rom. However as I do not own one, I cannot guide you how to do it.

[pabloingreece]

Hi gerald, in fact I did it already on a working cpc, let me show you on some screenshots. There is a ROM configuration using web interface, using 32 places for ROMS and there is a slot which can be used for loading a lower rom, I have loaded a spanish version of cpc 6128 rom successfully.


It's an amazing board, but the problem is that in the faulty cpc there is no change at all, so how can I achieve to use this board to "replace" the cpc problematic functionality? maybe there is no possibility, should I remove the PAL and close those jumpers you told me and remove the second bank of ram in order to test?


thanks!

[gerald]

Hi gerald, in fact I did it already on a working cpc, let me show you on some screenshots. There is a ROM configuration using web interface, using 32 places for ROMS and there is a slot which can be used for loading a lower rom, I have loaded a spanish version of cpc 6128 rom successfully.


It's an amazing board, but the problem is that in the faulty cpc there is no change at all, so how can I achieve to use this board to "replace" the cpc problematic functionality? maybe there is no possibility, should I remove the PAL and close those jumpers you told me and remove the second bank of ram in order to test?


thanks!

The idea is to put the ramtest as the lowrom and boot from it.
So just replace you spanish ROM with the RamTest.bin which is in the zip file on the thread I mentionned. You can also put in in a free slot and change the lower-rom-slot to that slot.
Do that when the M4 is connected on the working CPC, then test it on the non working CPC.

The test will let you know the working and failing RAM of the main bank. To be sure no RAM from the second bank is interfering, just remove them and test them in the 1st bank afterwards.

[pabloingreece]

Hi gerald, I made the changes you told me in order to test the main ram bank: removed the PAL and join the LK5,LK6 and LK8 jumpers. The results at first were the same, but I performed again a track test and found two broken tracks, after repairing the problem, the cpc boot "normally" with the following problem: the sound is retarded very much, when I press the del button the sound came but remains for almost 2 seconds! Also the floppy is not responding to CAT command, and in general the keyboard has too slow response... something else is wrong.

I'll maintain the configuration until find the problem, I've noticed the following, there is a capacitor near to the sound chip, which when I press it a sound appears, like a beep distorsed, also in the lower right part of the board there are two resistors (R111) near to the TC74HCU04P chip, when I put the finger the screen is totally distorsed. I refer these issues in order to detect what is wrong, maybe I need to recap the board...

Also I performed the test you told me with all the ram chips and the resutls were ok.

Finally, when I put the M4 Board with a modified lower rom other tha the ram test, or without any rom, the black border an grey background return again Without board, the system boots.

Thanks again gerald, your help was unvaluable! I think we are close to solve this mess!

PS I've attached some photos

[gerald]

Hi gerald, I made the changes you told me in order to test the main ram bank: removed the PAL and join the LK5,LK6 and LK8 jumpers. The results at first were the same, but I performed again a track test and found two broken tracks, after repairing the problem, the cpc boot "normally" with the following problem: the sound is retarded very much, when I press the del button the sound came but remains for almost 2 seconds! Also the floppy is not responding to CAT command, and in general the keyboard has too slow response... something else is wrong.

The keyboard and sound problem could be linked to an interrupt problem. Both are managed under interrupt.
Interrupt comes from the gate Array (40010).
1st you can check that there is no bad contact on the socket. You can also test it in your other CPC

I'll maintain the configuration until find the problem, I've noticed the following, there is a capacitor near to the sound chip, which when I press it a sound appears, like a beep distorsed, also in the lower right part of the board there are two resistors (R111) near to the TC74HCU04P chip, when I put the finger the screen is totally distorsed. I refer these issues in order to detect what is wrong, maybe I need to recap the board...

Putting your finger on the resistor near the 74HCU04P will for sure discord the screen. This is the 16MHz oscillator that drive the whole CPC. And putting you finger there will alter the oscillator frequency.

Finally, when I put the M4 Board with a modified lower rom other tha the ram test, or without any rom, the black border an grey background return again Without board, the system boots.

This may just need a good clean-up of the expansion connector.

[pabloingreece]

Good morning, I tested the "problematic/suspect" 40010 on the other CPC I have (the chip is exactly the same) and has no issue, playing with the 40010 of the damaged CPC normally, so it's not the 40010 at least OK. Can it be a matter of tracks? The next step is to change the 8255 & 74LS145 but I do not know if it's definitely the problem there.


About the M4 Board, it seems to be a problem with the contacts of the expansion port, when I put it 1-2 times BASIC 1.1 appeared when was pressed or moved, how can I clean/repair the tracks on exapansion port to make perfect contact?


Adventure continues ...

[pabloingreece]

Finally I found the problem, the R144 was broken, worked as an open interruptor and the INT signal was totally crazy.... When I replaced it, the Amstrad worked like a charm.


Thanks to gerald for giving me the hint!


PS. The expansion port was in good condition, after the resistor fix, the M4 board worked perfectly!

[LambdaMikel]

Finally I found the problem, the R144 was broken, worked as an open interruptor and the INT signal was totally crazy.... When I replaced it, the Amstrad worked like a charm.

Congratulations to fixing it!!