A500 KS3.1 Problem Solved

MC1173

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I could use a little help figuring out a problem I'm having.

Let me specify Computer specs first:

Amiga A500 (Rev6A)
512 Ram on Motherboard
512 Ram Trap Door Expansion
Fat Agnus - 8372A
Super Denise - 8373R4
CPU - 6800P8
KS Rom - 3.1(v40.63) or 1.3(v315093-02)


The problem starts with the 1MB Ram Chip Modification.

I located jumper pads J2 near the KS rom. I carefully cut the trace between the lower pads. I soldered a trace to bridge the upper two pads.

I located jumper pads J7 near the trap door Ram. I cut the trace between the lower two pads. This gave me 3 seperate pads.

At first I thought I had made a mistake, because the computer would not boot to KS screen, or floppy. So I reversed it and put it back to stock. After returning it to stock, it booted right up to the KS3.1 screen. So I attempted the modification again. I got the same results, with no boot screen. I decided to try swap out the KS3.1 Rom, with the original KS1.3 Rom. It booted fine. I then loaded up WB 1.3 to see if it was successful. Yup...WB was showing only one Ram at 863416 free Memory.

So both KS Roms work when Motherboard is unmodified, but KS1.3 is the only rom that works when Motherboard is modified.

I don't see what I'm doing wrong. Maybe someone else can spot it. Or knows something I'm missing.

Is there a modification I need to make to the KS3.1 Rom like what is need to make it work in the Rev5 board?

Any help would be greatly appreciated.
 

BLTCON0

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I don't see what I'm doing wrong.

Nothing. It ought to work.

Is the machine actually stable in its "working" 1 MB chip (1.3 ROM) config when you run a few programs?
What is the output of the "avail" command in a CLI window? Workbench 1.3 doesn't tell between different RAM types on its menu bar - it only shows the aggregate amount of RAM so you can't be sure it's "only one type of RAM". Run "avail" to make sure it's all chip and no fast.

Try softkicking KS 3.1 too, if possible (or use a different 3.1 ROM chip) - not really likely to be the problem but worth trying.

Double check that you haven't accidentally cut any traces near JP2. Check continuity for all address lines between CPU and ROM/Agnus/Gary (see the schematics for pin numbers).
 

motrucker

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It may be that you RAM card is not compatible with this upgrade. It sounds like you made all the right mods to the jumpers, so I don't know what's left. Sure hope this helps.
 

MC1173

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Ok, good to hear I don't seem to be missing anything.

BLTCONO - It seems to be stable in WB. I also tried a couple games to stress test it (Turrican 2, Shadow of the Beast). They ran fine. Played each for about 10 minutes.
I used the avail command you gave me. It gave me this: View attachment 86534
Looks like it is seeing it ok.
I don't know what softkicking is, so wasn't able to try that.
I agree with you, don't think it is the KS3.1 Rom. I just recieved it from AmigaKit.
I can order another KS3.1 Rom. If it doesn't work then I can upgrade my other 500A. That has a KS2.04 Rom.
I will have to buy a Multimeter, to check the continuity. I do not own one yet. Probably pick one up next week. Any suggestions for new user?
This will give me time to try and learn the schematics.




motrucker - I thought that at first too. But getting the same results from two different expansion RAMs. Also get same results when expansion RAMs are disconected before start up.



Not sure if this ifo will help. I notice that screen will go through a series of flickering. Mostly shades of black, like it is scanning. The red light on keyboard seems to match the screens erratic pattern with bright, and dim blinking.


Thank you guys for the input.
 

BLTCON0

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then I can upgrade my other 500A. That has a KS2.04 Rom.

Just for fun, try with the 2.04 ROM from that other A500.
If you're not bored, both under 1 MB chip and 512 KB + 512 KB chip/fast, to fully compare its behaviour.
 

MC1173

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OK, Ill give that a try when I get home from work tonight.
 

MC1173

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Well.....got good news and of course bad news.

Bad news

Is that the modifying, unmodifying has taken its toll on the jumper pads. Two have come loose.

Was going to solder some wires to pads and run them over to toggle switches I could access in the trap door.

Then I could on/off the modification without the wear and tear.

But not going to be able to do that now.



Good news


I was able get Modification on even when damaged pads.

I was able to test my KS2.04 Rom. It works modified and unmodified. I had to disable the jumper wire from 1 to 31 because it was from a Rev 5 motherboard.

I tested the KS3.1 in the Rev 5 Motherboard after making the modifications to work in that revision. It works great.

So im going to leave the KS2.04 in the modified ECS and the KS3.1 in the OCS.

Hopefully will get another 3.1 and test again later.



Thank you guys for your help.
 
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