A500 CHIP RAM ampliation.

[DyLucke]

I've fit the new Gary with the corresponding RAM expansion...

With this EXACT configuration, aside the changes i've made removing
the solder bridges, it always worked giving me 2mb, but only 512kb Chip.

The same GREEN SCREEN comes again....




I'll check the solder on the socket i've fit for the multiplexer just in case
as a last measure.

However, i SWEAR i've revised and i can AFFIRM SOLDER HAS BEEN
EFFECTIVELLY REMVOED FROM, JP2, JP7A, JP9, and the inner U32 bridges.
PLUS set an horizontal bridging on JP3 to make the board to look like
the one on the picture you've posted Zetr0.

It seems i can't achieve these stupid 2mb CHIP.

[DyLucke]

Bloody hell!!!!

Bad news chaps... After revising all the solder connections for the extra ram,
i've tried to do the same with the multiplexer, BUT when i was making it
out from the socket I SNOOZED... and as a result i broke one of the
legs of the tiny chip!!!!!!!!!!!!!!!!!!!!




Sorry Zetr0... i deserve some ...



I'll try to set 1+1 mb as it was described before...

But that will be tomorrow... It's late and i fear i could ruin some
other part now. I'm too stressed.

[Zetr0]

@Dylucke

I wonder if the socket underneath the multiplexer is causing too-much of a delay?

on the original A500+ theres no socket.. I can understand the memory being ok on sockets there latching / propagation has a wide skew rate, but the multiplexer is going to need bang-on timing (hence the need for an F varient of the chip (74F139))

I might be able to dig-up another multiplexer or ram chip if you need it, but I would see if you can make it happen without the socket for the Muxing chip.

[rkauer]

Also reseat the Agnus, it may be the culprit for those green screens.

[DyLucke]

Good morning there.
Well, this time (with better mood) i've tried to fix the stuff here.
Didn't get any improvement trying to set the miggy to 1+1 megs,
sadly i ruined the multiplexer, and i can't set it to 2mb chip...

I could make it fit creating some kind of "leg" using solder
or part of a needle and a solder blob once the chip is seated...

But it took me too much time and effort to do
all this stuff during last night and this morning since i don't have a proper
solder station nor a working bench with all the tools needed and i have
to improvise, sometimes i have to work on difficult postures since the
space in my room is too limited.

I've managed to return the mobo to the original state, and it
FINALLY works... Luckilly nothing got ruined.

However i don't think i will try to expand this miggy again,
at least at short term... I'm tired of soldering-desoldering and do
tests again and again, my room looked more like a soldering workshop
than a room for the last two days. And i have to say i wanted to expand
this miggy just to make a reasonable use of WHDLoad, but i've realized
I HAVE TWO A1200 THAT CAN MANAGE THIS TASK. So to mess around
with this "angry A500 mobo" is not a big deal. I'll let it be. I throw the
towel, mobo wins...

Definitelly there's something really OBVIOUS that we must have been
skiping... So obvious that we can't see it.

So, at this point i can only really sincerelly THANK you for your support guys
specially to Zetr0 who had the deference to send me a multiplexer.

Thank you so much. I hope i would be of some help for you on a future
situation.

Thanks again.

[yaqube]

Originally Posted by DyLucke

However, i SWEAR i've revised and i can AFFIRM SOLDER HAS BEEN EFFECTIVELLY REMVOED FROM, JP2, JP7A, JP9, and the inner U32 bridges.

Two lower pads of the JP2 should be connected together. Otherwise you get a green screen after power-on. Take a look at this picture: A500+ Rev.8A

[DyLucke]

Now you mention it, my board doesn't seem to have any track between the two
lower pads on JP2, as it didn't have any horizontal bridging tracks between
pads on JP3...

Maybe that's the thing i've been skipping. I'll try to check it later on, or tomorrow,
and post what i've found out. I'm tired of soldering, but definitelly this could
be the missing key i've been looking for.

As long as i've ruined the multiplexer, i'll try to set all the stuff for 1+1mb.
Let's see what happens, wish me luck.
Ha-ha.

[DyLucke]

Well, these are the results, i've taken in consideration what has been commented about JP2... We can clearly say THERE'S A MODEL OF BOARD, badged as Rev8A, that DOESN'T show any traces between pads at JP2 and JP3, i do assume the info we have about traces between pads at both points are related to Rev8A.1

That's what i've been skipping until now. But the fact is i didn't have been able
to expand the mobo... I did all the corrections needed PLUS EVEN, allowed myself
to make some experimentation leaving this or that open or closed on the related
JP's needed to expand the board... With no result.

Last time, bridging center and lower at JP2, clearing JP7, leaving JP9 alone (bridged)
and bridging vertically the pads at JP3 (II) and leaving U35 alone, i can say system
looked like it wanted to boot, clean white screen... a few seconds waiting, checking-up i guess, and when it was supposed to boot.. BANG, unknown colour flashing screen.

So i've returned the mobo to it's original configuration, i'll not try anything on it again...

Mainly because pads at JP3 after so many soldering-desoldering operations, probably
up to 20 have started to feel loose. It's a bit risky to mess with it after this.

So, sadly i'll let it be like this.

Thanks again for all the aid provided guys, i hope next time i come with
a problem we will be able to solve it.

God bless yah.

[DesktopDynamite]

Hi there sorry to bump this thread up again...
I have 2x A500, 1 rev 5 and another rev6a.
Both of them have been fitted with KS3.1 ROMs, Kipper's A508 fastmem board, and lastly an 8372A chips to expand their chipmem.

My question is, can I mod both to get 2MB chipmem or it does only apply to an A500+ model?

TIA.

Sent from my GT-I9301I using Tapatalk

[Zetr0]

@DesktopDynamite

Wow I haven't seen this thread in a while =)

Okay the 8372A can only address 1Mb of CHIP RAM.

To get to 2MB you would need an 8372B (or 8372AB) as these are pin compatible with the existing 8372A (not the 8370) which maybe on you rev 5.x

you will need to extensively modify the Agnus socket and motherboard to achieve this - there is a write up on AmiNet on how to do this - it is quite involved, one day I will do a how-to =)

I would suggest having a look on AmiBay as there are some 2MB clip-on upgrades for the Rev5.x and Rev 6a (and A2000) to give a further 1Mb upgrade to the machine, both the Rev5x and Rev6a can be modified for 1Mb CHIP =)

[DesktopDynamite]

Originally Posted by Zetr0

@DesktopDynamite

Wow I haven't seen this thread in a while =)

Okay the 8372A can only address 1Mb of CHIP RAM.

To get to 2MB you would need an 8372B (or 8372AB) as these are pin compatible with the existing 8372A (not the 8370) which maybe on you rev 5.x

you will need to extensively modify the Agnus socket and motherboard to achieve this - there is a write up on AmiNet on how to do this - it is quite involved, one day I will do a how-to =)

I would suggest having a look on AmiBay as there are some 2MB clip-on upgrades for the Rev5.x and Rev 6a (and A2000) to give a further 1Mb upgrade to the machine, both the Rev5x and Rev6a can be modified for 1Mb CHIP =)

Thanks for this handful and detailed information Zetro.

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