Will these RAM chips work for DIY upgrade?

[Astral]

To all you hackery expert people out there...

I've got an A500+. I'd like to do a DIY piggyback upgrade from 1mb to 2mb chip ram on the motherboard.

The onboard chips are 41c425680. I have 8 x spare 51425680 chips. Are these useable?

[Oldsmobile_Mike]

I thought that hack was just for the 500 to bring it up to 1MB, Does it work on the A500+?  Since your system is already set up for it, why not just add the extra 1MB to the trapdoor?  I see 1MB boards for the A500+ come up on ebay all the time.  Either way, good luck!  

[Astral]

You can take the 500+ from 1mb chip to 2mb chip on the motherboard.

Yeah, I thought of the trapdoor option...which is still an option...but I also love a bit of hackery! So thought I'd give it a go

[vince_6]

I have some A500 mobos. Two of them are plus.
I have also some Ram cards for the trapdoor. One of them is 512KB chip so my A500+ has now 1.5MB Chip. I don't know if your chips are compatible but if u can do the hack so u could add fast ram later through your trapdoor.
3 days ago I bough some chips for my A600 to add 2MB chip :-)

Goodluck mate.

[Astral]

@Vince_6

I intend to add fastram to the CPU socket. I've got a Kipper2k ram expansion on order

[Zetr0]

Off the top of my head,

To add an additional 1MB of DRAM (bringing to a total of 2MB) to the A500+ (A500 plus) motherboard you will also need to take the RAS and CAS from the piggy-backed DRAM chips (lift the relevant legs) and feed this to the RAS1 and CAS1 on the trapdoor slot.

You could easily achieve this by daisy-chaining 30awg wire from each RAS of the Piggy Backed RAM to the next - leading up to the trap-door, and then do the same for each CAS as well... I would suggest differentiating colours (Blue and Red work well )

That is all there is to it.... I would suggest checking the height of the piggybacked RAM chips in regard to hitting the underside of the keyboard.

[Astral]

@zetro...

You're right...without going back and reading it all now...it is something along those lines.

But my original question remains unanswered I have a feeling based on net searching that they are the same but I'm not 100% sure. Any idea?

[Zetr0]

From my research here is the following.

Your IC's should be compatible - I have checked these against the TMS44C256-80 that are on my A500+

Here is the pin out -




The pin-out to your chips can be found by clicking here

The RAS0 and RAS1 are not touched in the following augment only the addition of BCASL1 and BCASU 1 are used.

(big picture - sorry about that)




As you can see the banks are dealt with in blocks of 256k by 16 bit wide (512KB each bank)  The A500+ uses BCASL 0 and BCASU 0 for the 1MB of RAM on the motherboard.  And should there be RAM in the "trap door" expansion slot then it uses BCASL 1 and BCASU respectively for those two further banks.

512KB Expansions only make use of the BCASL 1 signal as far as I can work out.

Alternatively you could piggyback 512KB of ram on an A501 half-meg RAM upgrade (or clone) and just pull-up the CAS Pin (17) on the chips and then daisy chain this signal across the 4 piggyback chips and tie this to Pin 36 of the expansion bus for BCASU 1

[Astral]

Thanks Zetro.

Based on your info I plugged in a good ol' A501 equivalent and it shows as CHIP RAM. And your suggestion about a solder jobbie on top of the A501 chips is fantastic. That's the way I will do it!

[Zetr0]

@Astral

No worries, glad it helps.  I would suggest to buzz-out BCASL1 (pin 35) on the CHIP expansion bus - just to ensure that the A501 is using the Lower CAS (1) and not the Upper CAS (1).

Also - remember to take pictures for our fellow forum chummies =)

[Astral]

Zetro....calling yo Zetro...

I need some help please, if you don't mind.

I've found some time to start this hack. Bit of a long story as to what I've tried and what I haven't...

But can't get it to work so far. The things I can think of that are relevant at the moment are...

With BACSU 1...I am thinking that schematic is incorrect. I've found this...

http://www.1000bit.it/support/manuali/commodore/a500plus_sm/amiga500plus_sm.pdf

1) And it looks like pin 36 on the expansion connector is actually tied to pin 11 on U32...not pin 1. It visually looks to be the case on the actual motherboard I have too. I don't have my multimeter at home to check at the moment to confirm this. Regardless though...when connecting the jump wire to pin 36 the extra 512k is not recognised.

I have tried two different A501 type boards too. They are both clones.

2) I haven't actually soldered the RAM pins together yet, they are "force" fitted and appear to have plenty of tension on the pins to be making contact with the mating chips. I know, yes they should be solder, I will get around to soldering them just to be sure, but at this stage not sure how relevant this is???

3) You mention removing BACSL 1 (pin 35). Do you mean cutting the trace on the actual A501?

I've tried to link your info, the above PDF's info, various google searches and so on to work out what is wrong...but so far no success. I'll keep looking at that PDF to see what difference there are to the A501+ board compared to the standard A501 and I will also solder those chips...

HELP! Please Mr

*EDIT* All soldered now and still the same results...