A500 (r6a) 1MB CHIP RAM Modification: Caution dialup users: excessive H/W pr0n!

Zetr0

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Hello there my fellow AmiBayers

Recently I put up for sale a 512KB A500 Upgrade -

If plugged into a Basic A500+ it adds it to the CHIP ram (giving 1.5MB CHIP), however if plugged into a basic A500 it would add the 512KB as OTHER ram, thus leaving the precious CHIP ram at 512KB =(

Well we cannot have this so here is a modification that you can do at home with just a craft knife, two track cuts and a soldering iron.


Skills Required

1. Ability to handle a *sharp* craft knife
2. Basic multi-meter use *continuity mode*
3. Ability to solder one point


First Notice

This (HOW TO) is based on a Rev6a A500 motherboard, with an 8372a Agnus, If I find an older board I will do a how-to as well.

Second Notice

If you perform these alterations it is on your OWN ONUS; that means if kill the A500, you hurt yourself or others,or blow-up the street its YOUR FAULT, you do this on your OWN responsiblity


This disclaimer includes but is not limmited by you wanting or having the urge to sing anything by "Barbra Streisand", "Wham" or "Miami Sound Machine" has NOTHING to do with me.



Now, with that in mind we can begin =)
 
[update]

Sadly the sever housing these images no longer exists, as such some images have been lost.


Overview of the Mod



With Jumper location JP2 (cut and soldered)



with Jumper location JP7A (trace cut)
 
Last edited:
Before the Modifcation


heres JP7A (click to enlarge)


Heres what Workbench says (click to enlarge)



Need to get a *before* shot of JP2.... I forgot.... wheres that time machine got to?... i know its around here somewhere...
 
Modding Time


JP2 CUT
JP2-00.jpg



JP7A CUT
JP7A.jpg



JP2 SOLDER
JP2-01.jpg
 
After Modification


As they say on most cooking programs - is should look like this =D


JP2 (click for larger images)



JP7A (click for larger images)
 
Testing the Modification


JP2 - Cut (testing disconnection of pad 2 and 3)
JP2.jpg



JP2 - Solder (testing connection of pad 1 and 2) *click to enlarge*



JP7A - Cut (Testing disconnection of pad 2 and 3
JP7A.jpg
 
Making it Happen


So finally -

we have cut two traces and soldered two pads together -
we have also tested (continuity) to make sure our work is sound -

Whats next?

Turning it ON!!!!



Heres the Lashup - A500 with A501 and A500HC+ (8MB RAM)
jig2.jpg

(going to point out that the SCSI controller is connected to a SCSI->IDE adapter with a WinUAE formatted and prepped (OS3.1) on a 4.1GB HDD)



And there is LIFE!
jig.jpg




Whats Workbench Say? (tell me tell me TELL ME!!!!) *click to enlarge*




And there you have it, this took no more than 25 minutes to do AND I was taking pictures... this shouldn't take anyore more than 15 minutes in thier own home... just remember if in doubt ask before blowing somthing up.
 
dont have the ram cards yet can i pay any of you to do this for me ?
I will be geting two a500 in march also need 3.1 roms in them
 
this thread will be awesome to the max :bowdown:

Thanks my friend, this was a quick one -

Its important to note that IF one wanted to, you could populate the empty memory spaces at the bottom of the motherboard

jp7a.jpg


if you notice in the above picture, at the bottom of the board is the chip-memory - you will also notice that there are 4 unpopulated spaces -

With this mod - you can poluate those spaces with 4 20 pin 256x4 DIP memory modules - Thus rendering the trapdoor interface - for the most part - redundant.
 
Nice Tute chap,
I think anyone should be able to give that a go. :D
 
Excellent tutorial, my friend!

I'm still looking for some spare time to dig a go on turning the trapdoor expansion into FAST RAM and using the spare spaces on the mobo to expand the chip RAM.

An humble A500 with 1Mb Chip & 0.5Mb (not so) FAST is a lovely machine on its own.:)
 
With this mod - you can poluate those spaces with 4 20 pin 256x4 DIP memory modules - Thus rendering the trapdoor interface - for the most part - redundant.
Just to clarify - if you solder in 44256 chips, you need to apply the same jumper mods to get 1 MB of chip? And should they be 80 ns?
 
@MagerValp

Yes, to solder chips in place on the motherbaord you will need to perform this modification for it to be seen as CHIP ram, you can use any 44256 20pin dip of 80ns or faster =D

This Mod changes the memory location of the 512KB trapdoor slot - which also linked to the 512KB sockets on the motherboard, it moves the location from (SLOW) FAST RAM (cannot remember the $address) to be inside the 1MB CHIP RAM pool
 
if you notice in the above picture, at the bottom of the board is the chip-memory - you will also notice that there are 4 unpopulated spaces -

With this mod - you can poluate those spaces with 4 20 pin 256x4 DIP memory modules - Thus rendering the trapdoor interface - for the most part - redundant.


Hmm this was raised in another thread... about adding chips to the empty space... and I dont beleive it was concluded on whether chips could be just dropped in, or if resisters, similar to the ones already on the board, were required to be added along with the additional chips... ?

---------- Post added at 20:17 ---------- Previous post was at 20:15 ----------

Excellent tutorial, my friend!

I'm still looking for some spare time to dig a go on turning the trapdoor expansion into FAST RAM and using the spare spaces on the mobo to expand the chip RAM.

An humble A500 with 1Mb Chip & 0.5Mb (not so) FAST is a lovely machine on its own.:)


@Rkauer

Im confused. If adding chips to the empty motherboard memory slots along with performing this mod makes the trapdoor expansion slot redundant, how do you add the additional 0.5 mb after performing the 1mb chipram mod to total 1.5mb in an A500?
 
if you notice in the above picture, at the bottom of the board is the chip-memory - you will also notice that there are 4 unpopulated spaces -

With this mod - you can poluate those spaces with 4 20 pin 256x4 DIP memory modules - Thus rendering the trapdoor interface - for the most part - redundant.


Hmm this was raised in another thread... about adding chips to the empty space... and I dont beleive it was concluded on whether chips could be just dropped in, or if resisters, similar to the ones already on the board, were required to be added along with the additional chips... ?

---------- Post added at 20:17 ---------- Previous post was at 20:15 ----------

Excellent tutorial, my friend!

I'm still looking for some spare time to dig a go on turning the trapdoor expansion into FAST RAM and using the spare spaces on the mobo to expand the chip RAM.

An humble A500 with 1Mb Chip & 0.5Mb (not so) FAST is a lovely machine on its own.:)


@Rkauer

Im confused. If adding chips to the empty motherboard memory slots along with performing this mod makes the trapdoor expansion slot redundant, how do you add the additional 0.5 mb after performing the 1mb chipram mod to total 1.5mb in an A500?

I think you need an A500+ for that, or at least replace the Agnus chip on your A500 to one that supports 2MB. The normal A500 Agnus only supports up to 1MB ChipRAM.
 
I'll make a thread when my analysis ends.

For now, munch this bit of information: the trapdoor have just a few address lines, plus 16 data lines and the clock lines.

Slow-fast RAM on Amiga is found by asserting the right address area. This is made by Gary, not Agnus. It is just a matter of cutting traces on the trapdoor connector and route them to Gary, maybe adding some delay lines to RAS/CAS.
 
I did this mod, but I made it switchable, so that I could drop back to 512k CHIP + 512k SLOW RAM, for badly behaving programs.

The topmost pad of J2 actually peeled off the motherboard while I was doing it, so I had to follow the trace to another solder point to attach my switch wire.

It works well and I'm happy :)
 
@Zetro the A500 magician.......

Questions

How can i populate 2mb of chip to the r6a mainboard ?

I have a spare 8375 and 8373 denise.

I mean after the mod and after soldering chips on the mainboard i should be able to use the BaseBoard expansion correctly ? Or the trapdoor signal pins are useless ?

Note that the BaseBoard has 2 options by jumpers

a)Set to Agnus
b)Set to Fatter Agnus.

When set to Agnus all the memory from the Bboard goes as fast.

When set to Fatter (and depending) the board and amount of memory goes as chip.

By factory default on my r6a mainboard the second option does not work.
But if i change the Agnus with 8375 and do the mods along with the soldering of chips i will have a total of 2mb chip on my r6a. Is that correct ?
 
The problem is: Fatter Agnus (8375) is not pin-compatible with older Agnii.
 
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