CPC 464 Short circuit failure

[Retro Mecano]

Hello everybody,

I'm a new by in the forum, and also to the Amstrad world.

short presentation, I'm a retro gaming nerd with few years experience in restoring old gaming consoles (Nintendo, Sega, Atari, Neo-Geo etc..) so i got quite good soldering and repairing skills.

first time ever having an Amstrad, a CPC 464 (version 3, french azerty) with a CTM 640 color monitor. i started repairing first the monitor few months ago as it's my only opportunity to start with the CPC.
having succeeded with it, i started with the computer. first power on gives a grey screen, which indicates probably bad RAM according to what i have reead.

i started by tearing down the device and cleaning the whole mess (dust, dirt, spiderman webs, corrosion) and that gave me the same result. wiggling a little bit the Gate Array (40050) and the 40010, started to give random box colors and few garbage static lines.

it's a step ahead, and i decided to replace the chip through hole sockets because they were extremely corroded and might be the cause.

after putting the new ones, i powered on and the LED went red... for a second. and then nothing. it just died.

tried again, nothing. mesured the voltage from the 5V monitor PSU and they were solid 5. checked the power button, it was giving normal continuity. the 5v connector was also fine, i measured the 47uf cap, it was fine, and changed it anyway.

i rechecked the soldering on the socket for shorted rails, but nothing, everything is well in place.

the thing is when i power on the CPC again, the 5V input drops immidatly to 0, as it a was a security thing inside the monitor.

so i grabbed an external 5v PSU. tried to follow up the rail, and i could not figure out what was going on. all the board is shorted.

almost all ceramic capacitors were shorted! except few ones on the edge of the board.

there was no overheating chip. actually all were dead cold.

the 5V reached the connector to the tape, but nothing happening.

well, i am surprised specifically to the ceramic caps being shorted all at once.. how should i proceed?

[abalore]

It looks the power button is broken or most probably dirty. You can open it and clean it with alcohol.
If you want to be sure you can try first to short-circuit pins 1 and 3 of cassette connector (starting from top, but it can vary with the 464 model, so check these are the ones first)

[abalore]

About short circuit in all capacitors, it sounds very strange. Are you measuring the capacitors in place or you removed them first?

[Bryce]

My guess is that you damaged one of the copper through-hole rings on the top side of the GA socket when you swapped it and it's shorting two pins out. So the entire 5V rail is shorted to the GND rail. This would also make it look like all the ceramic caps are shorted and the only thing getting hot, would be a tiny piece of copper under the GA socket. If the GA is a 40010, I'd take a close look between the pins 25 and 26.

Bryce.

[Retro Mecano]

It looks the power button is broken or most probably dirty. You can open it and clean it with alcohol.
If you want to be sure you can try first to short-circuit pins 1 and 3 of cassette connector (starting from top, but it can vary with the 464 model, so check these are the ones first)

already done with no change.

My guess is that you damaged one of the copper through-hole rings on the top side of the GA socket when you swapped it and it's shorting two pins out. So the entire 5V rail is shorted to the GND rail. This would also make it look like all the ceramic caps are shorted and the only thing getting hot, would be a tiny piece of copper under the GA socket. If the GA is a 40010, I'd take a close look between the pins 25 and 26.

Bryce.

sound very plausible. i will recheck that as soon as i get back home.
and i (ironically) hope it's only that..

[Retro Mecano]

My guess is that you damaged one of the copper through-hole rings on the top side of the GA socket when you swapped it and it's shorting two pins out. So the entire 5V rail is shorted to the GND rail. This would also make it look like all the ceramic caps are shorted and the only thing getting hot, would be a tiny piece of copper under the GA socket. If the GA is a 40010, I'd take a close look between the pins 25 and 26.

Bryce.

Well, Bull's eye, mister Bryce.

I started dissoldering exactly Pin 25 from the socket of 40010 and guess what. It was a single hairwire from the dissoldering braid i used to remove the old socket, shorting with pin 26. Absolutly amazing. Thanks a lot!
I would never find this thing by my own.
You cannot view this attachment.
Now the serious problem: it's alive again, with the same issue. Random centered screen colors, or vertical garbage bars.

I tried to use the amstraddiag but i guess i am burning the wrong way the eproms. I used 27c128 and 27c256.

[Bryce]

I've definitely been doing this stuff far too long! But I'm glad you got it sorted out. That wire must have been glowing when the CPC was running! As for the initial problem, it's 99.9% a bad RAM. Just swap them all out.

Bryce.

[Retro Mecano]

I've definitely been doing this stuff far too long! But I'm glad you got it sorted out. That wire must have been glowing when the CPC was running! As for the initial problem, it's 99.9% a bad RAM. Just swap them all out.

Bryce.

I am quite sure also it's a ram. There is one getting warmer than the others.
Untill i find out replacements, i am still curious to get the Amstraddiag working.
The download has both 16k lower and upper files. 

I have only 27c128 eprom available. Tried sperately both roms and the system doesnt boot, only black screen.

What is the way to get it right?

[Bryce]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

[Retro Mecano]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

[Bryce]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

[Retro Mecano]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

[Bryce]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

[Retro Mecano]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

[Bryce]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

I have a Tunisian friend here (in Germany) that travels home regularly. Maybe he could bring a package over for you next time. I'll ask him when that would be.

Bryce.

[Retro Mecano]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

I have a Tunisian friend here (in Germany) that travels home regularly. Maybe he could bring a package over for you next time. I'll ask him when that would be.

Bryce.

That's very nice from your side, thanks!

But let me try first to find locally in some electronic junkyards, some time we find unbelievable stuff.

If i would be unlucky, then i'll come back to you.

Thank you Bryce!

[Bryce]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

I have a Tunisian friend here (in Germany) that travels home regularly. Maybe he could bring a package over for you next time. I'll ask him when that would be.

Bryce.

That's very nice from your side, thanks!

But let me try first to find locally in some electronic junkyards, some time we find unbelievable stuff.

If i would be unlucky, then i'll come back to you.

Thank you Bryce!

Then a quick tip: Many of the older cash registers (the ones before barcode scanners) are often dumped and are full of the same parts used in retro computers, including EPROMs and RAM.

Bryce.

[Retro Mecano]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

I have a Tunisian friend here (in Germany) that travels home regularly. Maybe he could bring a package over for you next time. I'll ask him when that would be.

Bryce.

That's very nice from your side, thanks!

But let me try first to find locally in some electronic junkyards, some time we find unbelievable stuff.

If i would be unlucky, then i'll come back to you.

Thank you Bryce!

Then a quick tip: Many of the older cash registers (the ones before barcode scanners) are often dumped and are full of the same parts used in retro computers, including EPROMs and RAM.

Bryce.

I managed to get an OTP AT27c256, and took the risk to bun the Diag.

Luckily it worked. Now i see 7 line with red bars. And it's stuck there.

What are the chances that alk RAMs are out?

[Bryce]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

I have a Tunisian friend here (in Germany) that travels home regularly. Maybe he could bring a package over for you next time. I'll ask him when that would be.

Bryce.

That's very nice from your side, thanks!

But let me try first to find locally in some electronic junkyards, some time we find unbelievable stuff.

If i would be unlucky, then i'll come back to you.

Thank you Bryce!

Then a quick tip: Many of the older cash registers (the ones before barcode scanners) are often dumped and are full of the same parts used in retro computers, including EPROMs and RAM.

Bryce.

I managed to get an OTP AT27c256, and took the risk to bun the Diag.

Luckily it worked. Now i see 7 line with red bars. And it's stuck there.

What are the chances that alk RAMs are out?

Unfortunately, that could really be the case. Because almost all pins are paralleled, the failure of one RAM could overload and damage the others. For example, one Pin is internally shorted to ground, so that essentially ties all paralleled pins to ground too. Either way, I usually recommend people to just replace them all as it's less hassle than going back in a few weeks to replace the next one that fails.

Bryce.

[Retro Mecano]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Where are you based?

Bryce.

In Tunisia.

We have a very strict policy for overseas purshasing.
I got one time a friend sending me some cheap 4164 ram from europe, i had to pay 10 times fees a the reception in customs office 👮�♂️😂

2€ chip costed me 20€. Worst GX4000 restoration ever🤷�♂️

I have a Tunisian friend here (in Germany) that travels home regularly. Maybe he could bring a package over for you next time. I'll ask him when that would be.

Bryce.

That's very nice from your side, thanks!

But let me try first to find locally in some electronic junkyards, some time we find unbelievable stuff.

If i would be unlucky, then i'll come back to you.

Thank you Bryce!

Then a quick tip: Many of the older cash registers (the ones before barcode scanners) are often dumped and are full of the same parts used in retro computers, including EPROMs and RAM.

Bryce.

I managed to get an OTP AT27c256, and took the risk to bun the Diag.

Luckily it worked. Now i see 7 line with red bars. And it's stuck there.

What are the chances that alk RAMs are out?

Unfortunately, that could really be the case. Because almost all pins are paralleled, the failure of one RAM could overload and damage the others. For example, one Pin is internally shorted to ground, so that essentially ties all paralleled pins to ground too. Either way, I usually recommend people to just replace them all as it's less hassle than going back in a few weeks to replace the next one that fails.

Bryce.

When does your friend travels back home 😂😂😂

[SerErris]

You need a 256. The Lower ROM (Firmware) file goes in the first 16K and the upper file, normally BASIC but in this case the Diag software needs to go in the upper 16k.

Bryce.

So in my mortal simple minded words😂

Is it:
copy /B Amstraddiaglower.rom+ Amstraddiagupper.rom Newfile
Or
copy /B Amstraddiagupper.rom+ Amstraddiaglower.rom Newfile

?

Wow, full points for old-school! I'd just open a Windows/Linux Hexeditor, import the lower ROM, then add the upper ROM after it and save it as a 32k file.

Bryce.

Then it should be the first option i guess.

Well, thank you very much for the support!

Now i will try to find out how to source both ram and 27c256 eproms. Not easy when you live in country where online purshasing is not possible.

Thumbs up for the forum and the reactivity!

I'll be back. 😎

Hi just to ensure that this is correct here, as I fell into the same pitfall myself on starting to work with the diag rom.

The diag rom is just different variants. Lower is if you want to boot the cpc from DIAG, aka dead CPC and hopefully it gives you information. You will not need the upper rom in that scenario.

Upper however is if you can get it to working state (e.g. Ready prompt) and you want to test other stuff (high memory, keyboard etc.). Then you can start it from the upper rom (not BASIC replacement). It is an normal expansion rom with a specific RSX command |DIAG

So you do not need to burn both. For your specific needs you can just burn the lower rom and you will be good. BASIC or any upper ROM is not required.