Help identifying ROM mod

VresiBerba · 15 July 2017, 00:46

What is this mod?

Daedalus · 15 July 2017, 01:13

It swaps A12 and the +5V lines. It must be something funky about those particular ROMs or that particular board - no A1200 revision I've ever seen had that mod. It's also got a layer of extra ROM sockets below them that's not normally there - I wonder if it's anything to do with them?

VresiBerba · 15 July 2017, 01:18

Quote:

Originally Posted by Daedalus

It swaps A12 and the +5V lines. It must be something funky about those particular ROMs or that particular board - no A1200 revision I've ever seen had that mod.

The board revision is 2B.

Quote:

Originally Posted by Daedalus

It's also got a layer of extra ROM sockets below them that's not normally there - I wonder if it's anything to do with them?

It's likely just to preserve the socket since it's an invasive mod.

Daedalus · 15 July 2017, 20:22

Yep, I've seen plenty of 2B boards and none with this mod. Good point about the sockets I guess - perhaps the ROMs were the wrong type and were fitted with those sockets at the factory/dealer to make them compatible with the standard ones, but it's a strange one given that they're original mask ROMs.

RedskullDC · 16 July 2017, 09:47

Quote:

Originally Posted by Daedalus

It swaps A12 and the +5V lines.

Referring to the datasheet for the MX23C2100 mask rom:
http://pdf1.alldatasheet.com/datashe...MX23C2100.html

It is swapping pins 38 and 32, which are signals A10 and A16.

Perhaps these chips are from a batch of mask roms that were programmed incorrectly?

Cheers,
Red

Daedalus · 16 July 2017, 18:50

Sorry - I miscounted, it's A12 and A18 that are swapped. I was speaking from the Amiga's perspective though - it (ab)uses the ROM addressing slightly differently to what you might expect by skipping two address lines. Anyway, I still have never seen such a setup other than on early A500s.

Sinphaltimus · 16 July 2017, 19:09

This is strange - My A500 Rev 5 has a 3.1 rom and it only has one trace wire.

Looking at my mainboard where keyboard = south and rear end = north, I have a wire going from the northern most left side of chip opin into a socket pin port on the right side of the chip a few pins down. I looked up A500 rom mods and they all seem to require 2 traces. So I'm not sure how this was modded before I got it but it works.

Can anyone explain?

Jope · 17 July 2017, 07:10

If it is a 3.1 mask ROM, then just the address line swap is needed, no bent pins + no second jumper. If it is an EPROM, then the 16bit mode jumper is needed, one pin is bent up and grounded.

FOL · 17 July 2017, 12:34

Ive seen lots of these. On different rev boards.
I have even seen them on CD32. So I would go with mis-programmed batch of chips theory.

VresiBerba · 17 July 2017, 13:18

Quote:

Originally Posted by FOL

Ive seen lots of these. On different rev boards.
I have even seen them on CD32. So I would go with mis-programmed batch of chips theory.

So factory mod, then?

Jope · 17 July 2017, 13:53

Quote:

Originally Posted by VresiBerba

So factory mod, then?

Yep, the one in your picture is a factory mod.

Sinphaltimus · 17 July 2017, 14:07

I'm certainly not trying to hyjack this thread but it seems more logical to keep similar questions here rather than spark a bunch of topics around the same subject.

Here's the single wire mod on my A500 Rev5. I'm guessing there was another modifications made for this on the mainboard someplace.b Possibly that JP2 mod. Not sure if that was for the chip ram Mod or not.

Jope · 17 July 2017, 14:34

In your case, the second wire is the grey conductive paint.

Even though it seems like a novel approach at first, I think this might be the result of mistakenly breaking off the pin while bending it. ;-)

VresiBerba · 17 July 2017, 14:40

Quote:

Originally Posted by Jope

Yep, the one in your picture is a factory mod.

Cool, thanks

Sinphaltimus · 17 July 2017, 15:25

Quote:

Originally Posted by Jope

In your case, the second wire is the grey conductive paint.

Even though it seems like a novel approach at first, I think this might be the result of mistakenly breaking off the pin while bending it. ;-)

OH, I hadn't noticed that - I honestly thought it was wear and tear of the chip being mishandled at some point. Thanks for the answer! Makes sense now. I could probably repair that and do a better job with the existing wire. But right now I'll stand by "if it ain't broke don't fix it".

Amiga1992 · 17 July 2017, 17:54

Quote:

Originally Posted by Sinphaltimus

IHere's the single wire mod on my A500 Rev5. I'm guessing there was another modifications made for this on the mainboard someplace.b Possibly that JP2 mod. Not sure if that was for the chip ram Mod or not.

I had this same mod on my rev5 and also asked about it before:
http://eab.abime.net/showthread.php?t=83728

RedskullDC · 01 August 2017, 15:50

An A1200 motherboard currently on Ebay:
http://www.ebay.com.au/itm/192263972958

Has the same "MX" chips, same wire mods. (Same colour green even!).

Cheers,
Red

idrougge · 01 August 2017, 23:54

I've seen those wires on MX ROMs before, but I can't remember if they were cut off or not.

TjLaZer · 16 August 2018, 22:00

Quote:

Originally Posted by Sinphaltimus

I'm certainly not trying to hyjack this thread but it seems more logical to keep similar questions here rather than spark a bunch of topics around the same subject.

Here's the single wire mod on my A500 Rev5. I'm guessing there was another modifications made for this on the mainboard someplace.b Possibly that JP2 mod. Not sure if that was for the chip ram Mod or not.

That's the normal procedure to get a Rev 5 A500 a Kickstart 3.1 ROM.

crazyc · 11 October 2022, 23:30

Sorry for resurrecting an old thread but I have just got an a1200 that came with the factory seal still intact. Upon opening it up I found the same mod to the roms, which are in a set of risers as far as I can see.
If I remove the roms in their risers does my motherboard effectively revert to normal?

15 July 2017, 00:46	#1
VresiBerba Registered User Join Date: Dec 2009 Location: Sweden Posts: 92	Help identifying ROM mod What is this mod? Last edited by VresiBerba; 15 July 2017 at 00:51.

17 July 2017, 14:07	#12
Sinphaltimus Registered User Join Date: Aug 2016 Location: Cresco, PA, USA Age: 53 Posts: 1,126	I'm certainly not trying to hyjack this thread but it seems more logical to keep similar questions here rather than spark a bunch of topics around the same subject. Here's the single wire mod on my A500 Rev5. I'm guessing there was another modifications made for this on the mainboard someplace.b Possibly that JP2 mod. Not sure if that was for the chip ram Mod or not. Attached Thumbnails

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15 July 2017, 01:13	#2
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	It swaps A12 and the +5V lines. It must be something funky about those particular ROMs or that particular board - no A1200 revision I've ever seen had that mod. It's also got a layer of extra ROM sockets below them that's not normally there - I wonder if it's anything to do with them?

15 July 2017, 20:22	#4
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	Yep, I've seen plenty of 2B boards and none with this mod. Good point about the sockets I guess - perhaps the ROMs were the wrong type and were fitted with those sockets at the factory/dealer to make them compatible with the standard ones, but it's a strange one given that they're original mask ROMs.

16 July 2017, 18:50	#6
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	Sorry - I miscounted, it's A12 and A18 that are swapped. I was speaking from the Amiga's perspective though - it (ab)uses the ROM addressing slightly differently to what you might expect by skipping two address lines. Anyway, I still have never seen such a setup other than on early A500s.

16 July 2017, 19:09	#7
Sinphaltimus Registered User Join Date: Aug 2016 Location: Cresco, PA, USA Age: 53 Posts: 1,126	This is strange - My A500 Rev 5 has a 3.1 rom and it only has one trace wire. Looking at my mainboard where keyboard = south and rear end = north, I have a wire going from the northern most left side of chip opin into a socket pin port on the right side of the chip a few pins down. I looked up A500 rom mods and they all seem to require 2 traces. So I'm not sure how this was modded before I got it but it works. Can anyone explain?

17 July 2017, 07:10	#8
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	If it is a 3.1 mask ROM, then just the address line swap is needed, no bent pins + no second jumper. If it is an EPROM, then the 16bit mode jumper is needed, one pin is bent up and grounded.

17 July 2017, 12:34	#9
FOL PSPUAE DEV Join Date: Nov 2006 Location: Wales / UK Age: 45 Posts: 5,999	Ive seen lots of these. On different rev boards. I have even seen them on CD32. So I would go with mis-programmed batch of chips theory.

17 July 2017, 14:34	#13
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	In your case, the second wire is the grey conductive paint. Even though it seems like a novel approach at first, I think this might be the result of mistakenly breaking off the pin while bending it. ;-)

01 August 2017, 15:50	#17
RedskullDC Digital Corruption Join Date: Jan 2007 Location: Dorrigo/Australia Age: 60 Posts: 355	An A1200 motherboard currently on Ebay: http://www.ebay.com.au/itm/192263972958 Has the same "MX" chips, same wire mods. (Same colour green even!). Cheers, Red

01 August 2017, 23:54	#18
idrougge Registered User Join Date: Sep 2007 Location: Stockholm Posts: 4,332	I've seen those wires on MX ROMs before, but I can't remember if they were cut off or not.

11 October 2022, 23:30	#20
crazyc Registered User Join Date: May 2012 Location: Gravesend - UK Posts: 927	Sorry for resurrecting an old thread but I have just got an a1200 that came with the factory seal still intact. Upon opening it up I found the same mod to the roms, which are in a set of risers as far as I can see. If I remove the roms in their risers does my motherboard effectively revert to normal?

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