Meet the Franken500!

[cheezmonkey]

Aww man, I just lost this post by clumbsily hitting the back button before I'd finished. Lame.

Let me start over...

A couple of months ago, I decided that my collection needed an Amiga. I had one half a lifetime ago, long deceased and haven't been part of the Amiga "scene" for just as long. As with most things in life, I rushed into it like a bull in a china shop and bought the first thing I saw - a very used A500. Not the wisest choice, but what can I say, I'm nostalgic like that. When I saw the exact same bundle I had as a kid on the otherbay, I'd hit buy it now before I knew what was what or had done an ounce of research. Soon realising I didn't know how to make it do a lot of the things I wanted out of it, I stumbled upon this wonderful place called Amibay, and haven't looked back. If it wasn't for you guys, I'd probably have given it up as a bad job, but instead I've pimped my 500 and it's just about to where I want to be. Special thanks go to FitzSteve for his invaluable advice along the way and indeed to many others.

So, what have I bought?

A very used, very wet A500, with A501 trapdoor (thanks Farcel2go)
A very shiny ACA500 (thanks Amigakit and FitzSteve for advice)
A KS 3.1 ROM (thanks again to the above)
A 2MB trapdoor expansion (again, thanks Steve)

Now for your viewing pleasure (and probably comic relief), I'd like to chronicle the journey with some pictures and werds.

I should imagine most people reading this have already disassembled the odd 50 or two, so I won't detail the teardown steps, instead, I'll start with a naked 500 mobo in the case and go from there. Time for the first picture methinks...

There she is. Rev 6a in case you were wondering. Pretty much stock, bar the 3.1 ROM:

There she is. lovely. Fitting that was one of the scariest jobs I've ever done, took me nearly half an hour to prize out the original 1.3 ROM!

Stock Gary and Paula, what a lovely couple they make!

Now for giggles... some rust :\ Stupid Farcel2go. Still, wouldn't be much of a Franken500 if it wasn't scarred and ugly now would it...

And a couple more shots of hideous corrosion:

The more eagle eyed among you would have noticed earlier that the contacts on the expansion bay are also fairly corroded. Frankensteins monster didn't live forever either...

Now, let's jump ahead to the fun bit. Here you can see the new Gary in his expanded socket, to allow addressing of the additional memory:

I had to move those two caps a bit and do some very careful prizing to get the old Gary out of there... These chips are stubborn. Note the flylead which goes off to.... My shiny new 2mb expansion!!

Notice there's what appears to be a passthrough connector. I thought for a minute I might be able to add the memory from the A501 to it, sadly they won't both fit in the trapdoor together. Oh well. It's all in, lets start rebuilding...

Floppy's back in.

That cursed metal shield is back in place. Note the delightfully corroded holding screws. They're about ten minutes away from dust. Sadly, I don't have any spares.

Keyboard back in. more rust visible on shielding. And marker pen because I have a terrbile memory and didn't want to connect the keyboard backwards

The 500's backside. It's got a hole in it. LOL, I'm such a child.

Yes, believe it or not, I do have the trapdoor cover, despite the state of the rest of it...

There she is. Right, now for the fun part. Does it work? Will it just catch fire? TO THE DESK!! (or dining table, whatever..)

The moment of truth is upon us. The air is thick with tension. My palms are sweating.... *click* goes the power switch. aaaaaand:

YEAAAH! First time! You little beauty. Of course, that doesn't neccessarily mean everything is in order. Let's boot something, see what happens. All I have to hand is a WB1.3 disk. It'll do.

OK. Half meg chip. check. Two meg expansion... no that's not qute right is it. Where's the other meg? bah, who knows. I've more things to plug in yet and besides it's half a meg more than I had with the A501 so it's progress. Right. What's next? Ahhh yes, the ACA500, what a wonderful invention that is. Let's get her in there!

Oops. Bloody amateurs. Let's try this again:

Much better. Right. But does it work?

Well, I do believe it does. What does it think I have installed? Well again, 512+1024+1536 = 3MB. Well... it'll do for now. Back to the menu:

I note that 1M chip ram expansion is currently "unavailable" not sure it was like that before or not. Ah well. Details. Does it start?

Why yes it does. It even appears to have as much RAM as I was expecting it to, based on the previous screen.

Does it run stuff? Well yes. I took a picture of the title screen of Golden Axe, but you don't need to see that.

Ah who am I kidding, of course you do!!

So there we have it. The Franken500 lives, but much like Frankenstein's actual monster, it appears to lack the mental capacity I'd hoped for. That said, it does do yet more things than the previous setup did with the half-meg trapdoor expansion.

Any suggestions on why the 2mb card is only showing 1mb would be very welcome. Perhaps I need to adjust the jumpers on the Gary card? Any guesses as to what they might be for would be appreciated as I have no accompanying documentation for the expansion.

Thanks to all involved in getting this far, your help is truly appreciated.

 

[Merlin]

The available memory may be down the the version of the Agnus chip you have. A500 Pluses had an 8375 'Fat Agnus' that allowed up to 2Mb Chip RAM to be used.

http://en.wikipedia.org/wiki/MOS_Technology_Agnus

If you fit a later 8372A Fat Agnus to your A500, any memory above 1Mb is seen as Fast RAM, not Chip RAM on the A500. You may need to change a few links and jumpers to be able to address 2Mb Chip Ram on your machine and there are gurus such as Zetr0 that can help you out here.

Careful - some versions of Agnus chips (Agnii?) such as the 8375 from the A500 Plus may not be pin compatible with your Agnus socket - it's best to check your existing one and post what version you have, so that we can advise as to which later ones are compatible.

 

[cheezmonkey]

Thanks Merlin, that's most informative and does go some way to explaining why I can't see it all. As you can see in one of the pics, my Agnus is 8372A 318069-02 which would appear, as you say, to only support 1MB chip ram. I'll wait and see whether Zetr0 wades in, as you suggest

 

[fitzsteve]

Hi Mate, that looks pretty sweet.

I'm sure someone with the knowledge will help you get the extra Ram to show, the ACA should have it's full 2mb Ram with Maprom off, I wonder why it's only showing 1.5mb? You should really have 3.5mb total with the current settings and then 4mb once we figure out the Trapdoor Ram board :dry:

 

[roy_bates]

your motherboard has 512kb on board and 1mb in the trapdoor although there seems to be a board missing on that card.

your agnus will only support 1mb max as chipram.


and the only way to expand chipram is to get a megachip or similar.

 

[cheezmonkey]

the ACA should have it's full 2mb Ram with Maprom off, I wonder why it's only showing 1.5mb? You should really have 3.5mb total with the current settings and then 4mb once we figure out the Trapdoor Ram board :dry:

Yeah, that's been bugging me since I got the thing. I'd assumed it was becuase 512k is reserved for MapROM perhaps whether its on or off, but if I enable it, it does use an additional 512k...

 

[Sardine]

and the only way to expand chipram is to get a megachip or similar.

Or get an A500+ with 1mb extra ram.

 

[cheezmonkey]

there seems to be a board missing on that card.

What makes you say that?

 

[roy_bates]

there seems to be a board missing on that card.

What makes you say that?

the passthrough is empty.

 

[SaviorX]

there seems to be a board missing on that card.

What makes you say that?

14256 (128kb) chips x8 = 1024MB btw..it's a 1meg card.

(256,000 x 4-bits (nybbles) )

(is there some other ram on the chip/expansion that is powering it tho? i am guessing not)

 

[roy_bates]

the passthrough was for a 512kb card with disable.

 

[cheezmonkey]

there seems to be a board missing on that card.

What makes you say that?

14256 (128kb) chips x8 = 1024MB btw..it's a 1meg card.

(256,000 x 4-bits (nybbles) )

(is there some other ram on the chip/expansion that is powering it tho? i am guessing not)

Interesting. And would explain a lot.

---------- Post added at 18:03 ---------- Previous post was at 18:02 ----------

the passthrough was for a 512kb card with disable.

Sorry Roy, I don't catch your meaning entirely...

 

[roy_bates]

a 512kb card plugs in the back of the 1mb card,the pins on the back of the 1mb card is a passthrough mate.
and the 512kb card had a switch which turns it on or off.

i cant make it anymore simpler than that

 

[fitzsteve]

Ahh cool so you can use an existing 512k Ram board with it, cheezmonkey's A501 wont fit.

Shame you sold that small 512k board already Roy! You don't have any more do you?

 

[roy_bates]

Ahh cool so you can use an existing 512k Ram board with it, cheezmonkey's A501 wont fit.

Shame you sold that small 512k board already Roy! You don't have any more do you?

i'll have a look a bit later mate im still having a clear out.

if anyone has one thats broken i can fix it.

 

[fitzsteve]

Thanks Roy, I want to try and get one for cheezmonkey

 

[cheezmonkey]

Aww shucks. Thank you guys.

 

[rkauer]

Welcome to site!

As Roy already told you, the board you have is a RANGER MEMORY expansion. Although it is not true FAST RAM, it is not chip RAM, either. Oh, the expansion you have is a Zydec Megaboard or similar. Again, you must do a small surgery (if not already done) to force the Agnus 8372A to recognize 1Mb chip RAM after inserting a proper A501 equivalent (short enough to fit physically, obvious).

Without the mentioned hack (Zetr0 can provide images ;-)) if you add another 512kb expansion board you'll have 1.5Mb of Ranger memory (also known as slow-fast RAM). But for higher resolutions, applications and the odd game that require 1Mb chip RAM that will not work.

Most games from the OCS era (A500/ROM 1.3) wants Ranger memory, so keep it!

 

[roy_bates]

just to help out a bit more.

the jumper mentioned by rkauer is jp2,some gary adaptor cards wont like that config though.
your millage will vary.
and may also conflict with these cards if the motherboard has 1mb of ram installed and may cause the system to not boot.

 

[coltch]

That's nearly the same setup as one of my A500's although I have the additional 512kb board with the disable switch. I tend to use my other A500 with the ACA500 as it only has 512kb in the trapdoor and I use the chipram option for 1mb.