CPC 6128 with RAM issues, can it be saved? UP: Yes, It's alive and kicking!

[Cucurbitacée]

Hi guys,
So I was given a broken 6128 like 25 years ago. Back then I already had a working 6128 and didn't put any effort into it. Fast forward to last Christmas where my mother told me to "clean up my shit in the attic", part of it being  the 6128. So the broken 6128 is back on the table...


I plugged it and got a "grayish" screen with a black border. A quick search lead me to this very forum to point a memory issue.


I removed the HAL and bridged the correct pins to use the second RAM bank. I got the Basic Prompt! Brillant, so I order a lot of RAM chip.


I replaced the chip that was giving an inconsistent reading with a super cheap oscilloscope (please note I don't really know how to use it, I was following instructions found online).


For one second, I believed I fixed it! Unfortunately after briefly showing the Basic text, the screen went all blue.


So I change every other chip, testing the computer after each one. Same result.


To be sure, I removed the HAL and use the hack again and was able to load a 64K game from a Gotek without issue.


My very limited understanding of the 6128 tells me the HAL is defective... So I looked for a replacement online, and found... nothing.


So in a bit of last resort, I registered here hoping that someone can confirm or give a better diagnostic. So I know if there is still life in this 6128 or if it is destined to be salvaged for parts...


Here is a video of the two random behaviour. It either freezes before the READY prompt or disappear to blue.


https://youtu.be/kCDiJwq4a1w


Thanks in advance!

[Bryce]

Hi,
are you sure you swapped the correct bank of chips?

Bryce.

[Cucurbitacée]

Ah, good question. As mentioned before, I don't know much about CPC. I did the same as mentioned in this topic:
https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/video-forcing-2nd-ram-bank-on-the-amstrad-cpc-6128/

[Bryce]

The bank you should have changed is the row on the right.

Bryce.

[Cucurbitacée]

That's what I did, sorry I misread your first answer and understood I may have done the wrong HAL hack. To confirm, I changed IC127 to IC134.

[Bryce]

Ok. Are you using an Amstrad monitor to power the CPC or some modern PSU?

Bryce.

[Cucurbitacée]

I'm using the Amstrad 644 monitor that I used regularly with my working 6128.

[Bryce]

It could be the PAL then. This can be replaced with a programmed GAL, the code is available somewhere here.

Bryce.

[Cucurbitacée]

Thanks, I'll have a look. Any recommended chip, by any chance?

[Bryce]

The code is for a GAL16V8C. Here's the JED file (not my work).

Bryce.

[Cucurbitacée]

Thanks! I've ordered one. Out of curiosity, PAL chips seems to be more common and easier to find, would the same code be compatible?

[Bryce]

Yes, the code would be compatible, but you've got to be really careful where you buy the PALs from. I wouldn't buy them from anyone but a real distributor (ie: Mouser / Digikey etc).

Bryce.

[Cucurbitacée]

Good to know, thanks! Anyway, I've ordered a GAL and will update this thread when I'll receive it.

[Skunkfish]

Out of interest could a Microchip ATF16V8C be used? (https://www.microchip.com/wwwproducts/en/atf16v8c)
These are still in production...

[Bryce]

Out of interest could a Microchip ATF16V8C be used? (https://www.microchip.com/wwwproducts/en/atf16v8c)
These are still in production...

Yeah, it can replace (emulate) a PAL16V8.

Bryce.

[Cucurbitacée]

Hi,


The GAL I've ordered finally arrived. And the CPC is now working like a charm!
So this CPC had both a RAM chip and the HAL defective. Many thanks to Bryce for taking the time to help some random person on the Internet, you rock. Now I can finally watch the demos that are not running on my other (cost-reduced) 6128.

[Bryce]

Glad you got it sorted, random person on the internet*.

Bryce.

* The fact that you are interested in the CPC and joined our community automatically removes your "randomness" and makes you "one of us"