Testing HM65256 pseudo SRAM

[TheDaddy]

Anyone any ideas how to test a HM65256 Pseudo ram from a CPS1 Board ?? My TL866 does 61256 & 62256 but fails on every chip. Pinout is the same mind, I am assuming its a little different internally. I have read up on the ram but to be fair I am none the wiser really

Any help appreciated,

Dave.

 

[Ace`]

You can test it as 62256 iirc.

 

[TheDaddy]

Thanks for the reply Ace , I thought so too , I know 62256 & 61256 are different (I didnt say I had tried them both incase) But looking at pin outs they are correct :-

65256 pinout



62256 pinout



The actual chip



And the actual result



The PCB runs but has Graphics issues (on one PCB it says Color ram bad ! Never seen that but still), this is the SRAM I only pulled it as it was socket as should not have anything to do with graphics ?? Not as I have done much on these boards yet , I was just having a bit of a play today.

Unless I am that unlucky all 6 I have pulled are faulty ?? But board would not boot surely ??

Arghhhhh, I get confused.

Dave.

 

[Ace`]

not my work, can't remember where I downloaded it from now I just translated it as it was in French originally.

I don't know how accurate it is as the colour ram is actually the 6116 rams closer to the dip switches.

 

[TheDaddy]

Oh brill that will come in handy cheers. Ordered some 65256 see what they test faulty.

Dave.

 

[Georgian2]

Don't you have another game to test it? Most of the time I put RAMs in another known working boards and see what if they work.

 

[Ace`]

From what I remember the pseudo ram is a funny beast and when it's used in pseudo mode it has to be 65256 but usually it's just used in standard mode as a 62256. I think the only time I've seen where it actually needed to be 65256 was Outrun, but usually 62556 will work. Some of my terminology might be off but that's how I understand it.

Sega must have bought in bulk (maybe for Outrun? hehe) but you can take the two 65256 rams from a Mega Drive and replace them with 62256s, as they're getting quite hard to find now.

 

[TheDaddy]

Don't you have another game to test it? Most of the time I put RAMs in another known working boards and see what if they work.

Dont have anything socketed. I will sort a test board out.

Dave.

 

[Georgian2]

I run into same problem now.
https://www.ukvac.com/forum/threads/tc51832spl-85-pseudo-sram-replacement.86069/

 

[TheDaddy]

Welcome to the party ! Lol

Dave.