Grey box black border when cpc464 is switched on

[morley27]

Hi there, lastnight my amstrad cpc464 froze whilst playing a game, i switched the unit off and back on and now this grey box with black borders appears on screen.

The mother board is MC0044A

I have ordered a new Z80 chip in the hope this fixes the problem, but if someone knows of anyhelp and can maybe break it down in to a more simple term for me, Im new to this, i mean, is it a case of simply replacing a chip? Any help would be grateful!!

[Munchausen]

Oh dear, that isn't good news. It sounds like something is fried, but probably not the Z80. This seems to normally be a symptom caused by putting too high a voltage into the 5V socket. See this thread


Additionally, I'd be somewhat concerned that it happened during normal use... maybe there's a short somewhere or something.. you haven't spilt some liquid or something on it? Maybe a RAM/ROM chip just died because it's old? Maybe Bryce or someone else with better knowledge of the hardware can provide more info as to why this might have happened?


Good luck!

[morley27]

Hi there thanks for the reply, i have use to a higher voltage than normal, that must of caused it, what do i need to replace to do this?


When you say RAM/ROM chip, where are these located on the circuit board? are these the chips where there are about 8 lined up in a row? Cheers

[steve]

You can download the service manual here,
Service Manuals - CPCWiki

8 identical chips are the ram chips.

[Marq]

Welcome to the grey/black club... I'll try to change the memory chips on my 6128 as soon as possible and report if it helps.

[morley27]

Cheers Steve,

Marq, i want to leave this club I have joined quickly!!! 

[Bryce]

Hi there thanks for the reply, i have use to a higher voltage than normal, that must of caused it, what do i need to replace to do this?


When you say RAM/ROM chip, where are these located on the circuit board? are these the chips where there are about 8 lined up in a row? Cheers

How high was the voltage you used? It couldn't be much if the CPC was working for a while at the higher voltage.

Chances are, it's a RAM IC that's died, yes, that's the row of 8 chips. Try turning on the CPC and feel if any of them are getting hot. Although if they were all running at too high a voltage, chances are, they are all slightly damaged, so I'd swap them all.

The ROM IC's can take some overvoltage as long as the polarity is correct, so these are probably still ok.

Bryce.

[morley27]

Hi Bryce,

Nice one, The voltage was 8.4, was working for a few days/ few hours a time, then it crashed as i was playing, now i have this screen,

Well I already have a new Z80 chip coming, I will try that,

I plugged the adapter in and all the rom chips get hot, some of the too hot to touch!

This may cost alot to get 8 of these chips, any recommendations as where to get them from? Do they have to be the exact KM4164B-15? Or are there alternatives that do the same job? You have been a great help, p.s, i have ordered a 5v amp adapter! 

[morley27]

Sorry, I meant the Ram chips get hot.

~Which ones are the rom chips then?

[Bryce]

ok, at 8.4V you've definitely killed all the RAM and possiibly other ICs too. The ROM chips are the larger 32 pin devices with Amstrad and the numbers 40015 and 40025 written on them.

If you haven't done much soldering before, this isn't an easy fix. chances are that some logic has died too and that might be difficult to find.

Did you knowingly run it on 8.4V ??

Bryce.

[Munchausen]

The ROMs are bigger than the RAM ICs, maybe around 1.5x3cm (same width as z80, but not as long). I don't know if the 464 has 1 or 2, the 6128 has 2. But not the AY-xxxxx which is the sound chip. I think the ROM for the 464 will say 40015 on it. But it seems it is more likely the RAM has died than the ROM. EDIT: ninja'd by Bryce!


Look here for part numbers: Amstrad part numbers - CPCWiki


And here for pictures: Mainboard Versions - CPCWiki


I don't know if the RAM must be an exact match. I did find that the KM4164A-15 is available for much lower prices and might work (same pinout and theoretically same response time), but according to this page it needs a more frequent refresh than the B variant and so may not work (and though I didn't see anything about this in the chip datasheets I didn't examine any timing diagrams in much detail).

[morley27]

I have done plenty of soldering, getting the chips out and in are no problem,

I have just gota find out where they sell these KM4164B-15 chips,
I have found these 

MK4116N-3IRL  GP,
MCM4164BP15  
Would these do the trick?

you have all been very helpfull!!

[Bryce]

You can't use 4116, they need 5V, 12V and -5V, not to mention the fact that you would then have a 16K CPC
(These are the ones used in the 48K Speccy)

But any 4164 should do. The CPC refreshes them fast enough for even the picky ones.

M5K4164-15 ANP by Mitsubishi, 64Kx1 Dynamic RAM, 16 pin, 0.3" DIP, 18 available

Edit: Just read the Mutant Catepillar article. You should never use mixed types of RAM, it's always a bad idea.

Bryce.

[morley27]

Cheers Bryce,

So It would be best to buy 8new x 4146 so at least there is no mixing of ram.

Please forgive my ignorance of the terminology for chips and so on. Still learning. 

[Bryce]

Yes, it's best to buy them from the same source.

I just double checked the Datasheets of the A type. It needs to be fully refreshed at least every 2ms. The CPC refreshes approx every 16µs so even the fussy ones would easily work. I've no idea why Mutant Catepillar was having problems, because the Spectrum also refreshes fast enough for the A type. Maybe he can shed some more light on the exact cause (He's known as Spirantho in this Forum).

Just for info - RAM chip names tell you exactly what they are:

Ignore the first Number (4)
4116 -20: 1 Bit, 16K - 200ns
4164 -15: 1 bit, 64K - 150ns
4464 -12: 4 bit, 64K - 120ns

Remember that with the speed, smaller is better, so you can replace a -15 with a -12, but not the other way around.

Bryce.

[ralferoo]

The CPC refreshes approx every 16µs so even the fussy ones would easily work. I've no idea why Mutant Catepillar was having problems, because the Spectrum also refreshes fast enough for the A type.

From reading the Spectrum ULA book, the Spectrum actually uses the RAM out of spec. I can't recall the specifics, but the video accesses are done as two bytes to pixel memory and two bytes to attribute memory, so that it can leave the same row selected and use 3 cycles to fetch 2 bytes at a time. And I think the time spent in each CAS cycle is slightly quicker than is required, so it wouldn't work with slower chips and arguably shouldn't have worked with the chips that got into retail speccys.

[Bryce]

That's true, but that was ZX Spectrum, using 4116 RAM (A great book, read it too ). The computer that spirantho was referring to is the Spectrum +2, a completely different situation, almost an Amstrad.

Bryce.

[MaV]

almost an Amstrad.

*cough* Come again?

[Bryce]

Well it does say Amstrad on the PCB

Bryce.

[MaV]

Well it does say Amstrad on the PCB

Fair enough.

[Gryzor]

I don't think it's worth fixing... better scrap it and sell it for parts. Send me the key caps, please.


[/innocent whistling]

[steve]

Why not get a cheap PC keyboard and use the caps off of that?

[Gryzor]

Why not get a cheap PC keyboard and use the caps off of that?

Where's the fun (or the colour) in that?

[Bryce]

Why not get a cheap PC keyboard and use the caps off of that?

Because the caps on almost every single keyboard are different. I don't think I've ever seen two keyboards where the keys were swappable.

Bryce.

[steve]

Because the caps on almost every single keyboard are different. I don't think I've ever seen two keyboards where the keys were swappable.

Bryce.

I am sure any keytops will fit on his fridge .