CPCWiki forum

General Category => Technical Support => Topic started by: Cucurbitacée on 19:27, 13 January 21

Title: CPC 6128 with RAM issues, can it be saved? UP: Yes, It's alive and kicking!
Post by: Cucurbitacée on 19:27, 13 January 21
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 (https://youtu.be/kCDiJwq4a1w)


Thanks in advance!
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 19:30, 13 January 21
Hi,
are you sure you swapped the correct bank of chips?

Bryce.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 19:33, 13 January 21
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/ (https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/video-forcing-2nd-ram-bank-on-the-amstrad-cpc-6128/)
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 19:37, 13 January 21
The bank you should have changed is the row on the right.

Bryce.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 19:41, 13 January 21
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.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 19:52, 13 January 21
Ok. Are you using an Amstrad monitor to power the CPC or some modern PSU?

Bryce.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 19:55, 13 January 21
I'm using the Amstrad 644 monitor that I used regularly with my working 6128.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 20:43, 13 January 21
It could be the PAL then. This can be replaced with a programmed GAL, the code is available somewhere here.

Bryce.
 
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 20:49, 13 January 21
Thanks, I'll have a look. Any recommended chip, by any chance?
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 21:08, 13 January 21
The code is for a GAL16V8C. Here's the JED file (not my work).

Bryce.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 21:16, 13 January 21
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?
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 10:40, 14 January 21
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.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 18:43, 14 January 21
Good to know, thanks! Anyway, I've ordered a GAL and will update this thread when I'll receive it.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Skunkfish on 19:19, 14 January 21
Out of interest could a Microchip ATF16V8C be used? (https://www.microchip.com/wwwproducts/en/atf16v8c)
These are still in production...
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Bryce on 21:18, 14 January 21
Out of interest could a Microchip ATF16V8C be used? (https://www.microchip.com/wwwproducts/en/atf16v8c (https://www.microchip.com/wwwproducts/en/atf16v8c))
These are still in production...

Yeah, it can replace (emulate) a PAL16V8.

Bryce.
Title: Re: CPC 6128 with RAM issues, can it be saved?
Post by: Cucurbitacée on 18:55, 21 January 21
Hi,


The GAL I've ordered finally arrived. And the CPC is now working like a charm! :D
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.
Title: Re: CPC 6128 with RAM issues, can it be saved? UP: Yes, It's alive and kicking!
Post by: Bryce on 19:29, 21 January 21
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" :)