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Old 02 April 2015, 22:44   #1
kipper2k
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Amiga 500 mod to Amiga 500+

Hi All,

seeing as my laptop is dying i decided to find something else to keep me occupied for a while.

I remember there was that one Christmas that Commodore ran out of Amiga 500s (I think they had to pay their bar bill) They shipped out A500+ motherboards (Rev 8A) that were crippled so as to make them into a basic A500.

This is probably the best news that people with this board have heard because there was no clock circuit on board and no battery so no corrosion and their boards are probably in pristine condition.

So, here is the good news, i myself have one of these boards and decided the time was right to convert it into a fully fledged A500+ (without the nasty clock circuit populated)


edit. i also changed some caps.. laid them flat so they wouldn't interfere if i was to add a board on top of the CPU

Board is now updated and it works perfectly as a 1MB A500+. I took pictures of the upgrade process and i will post them in this thread in the next couple of days, here is a picture of the finished product...

if you notice i also shamelessy added my 1mb chipmem board with RTC circuit as free advertising lol



I'll post a tutorial with parts info etc so people can do their own.

Here is a picture of the finished upgrade...




here is supersized completed board

4 ram chips need to be added, 1 logic chip (the one to the right of U35), and some jumpers altered, more info when i get time.... difficulty scale is about 7/10. As you can see the clock circuit is there, just never been populated. This board is in very nice condition (It's a keeper

i also changed the caps on the left side of the board and laid them flat so they wouldnt interfere with any addon boards that may be coming


One thing to note... Commodore also replaced the Denise from an a500+ (the 8373) with a regular 8362 found in eearlier a500 models


----------------------------------------------------------------------------------------------

Tutorial...

Here is a picture of the original untouched motherboard, all areas circled in yellow have changes that need to be made




here is supersized original untouched board

Solder blobs need to be removed from ;

JP2
JP3
JP7A
2 solder blobs at U32
JP9 (Do not touch unless you want to rebuild the clock circuit)


Remove all solder from the IC holes from U19, U18, U17, U16 and U32

To remove the solder from holes and pads take your time, do not rush, and you do not need a very hot iron, you just need it hot enough to melt the solder, too hot an iron can damage the pads.

You will need desoldering braid, rosin flux, isopropyl alcohol and a mechanical solder sucker. You have a few options to clear the solder out of the holes, you can use rosin flux to wet all solder pads and use the iron and desoldering braid to wick the solder out of the holes. You can also heat up the solder and then use the solder sucker to remove it. Both methods can work as good as each other. pads that are on the ground plane are particularly annoying to clean out as you need a bit more heat to suck out the solder due to the ground plane acting as a heat sink and sucking the heat away as you are trying to heat it.

Once the blobs are removed and the IC holes cleaned out, clean up your work with Isopropyl Alcohol and paper towel/q tips top and bottom. Inspect all IC holes to make sure the traces are not damaged (hence why we don't like high heat). So now you have a few options...

You can use 20 pin dip sockets and solder them in the motherboard or solder the new RAM chips directly into the board.

problems with either method...

- soldering untested ram chip to motherboard could cause issues, if ram chip fails its a pain to replace...
- soldering a socket to motherboard increases height of chips and will touch underside of keyboard, you will need to grind off some plastic off the chips to close case properly.

the MC74F139N IC can be socketed (16 pin) with no issues

the RAM chips required are 256K x 4bit 20 pin chips (I used TMS44c256-10N RAM chips)

Once you have added the RAM chips and U32 it is now time to redo the jumper pads to their new setting... Look at supersized picture of the first image to see the correct orientation

JP2 - bottom 2 pads need to be blobbed together
JP3 - top left and top right pad blobbed together
- bottom left and bottom right blobbed together
jp7a - does not need any bridging, leave open
JP9 - do not touch

If you want me to supply the parts then i can order the RAM chips, sockets and logic chip for you, The parts are not that expensive and of course they would be pretested to make sure they work. I can also provide somee replacement caps if required

-------

Last edited by kipper2k; 05 April 2015 at 15:09.
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Old 02 April 2015, 22:48   #2
tassel
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Hi kipper2k,

I also have one og these Rev.8A 500 boards without the clock circuit. Is it much work to convert it to an A500+ ?

Looking forward to see some pictures
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Old 03 April 2015, 00:35   #3
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You have to clear pin holes (standard solder vacuum sucker works fine) on four memory chip spots and one logic IC go so you can put sockets there. You can put chips in their birthday suits but sockets can make it easier in the long run.

That's the hardest part, adjusting jumpers is rather easy. I guess it takes a bit of time the first time you do it, but all in all it wasn't that hard. I did it about a year ago on mine.
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Old 03 April 2015, 10:24   #4
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The jumpers can be cross referenced from any of the big pictures of a500+ boards on bboah with the aid of the schematics. This is less than 7/10 in difficulty imo. :-)

Perhaps I'm weird, but I'd populate the clock too, perhaps with a coin cell. The clock isn't wretched, it's the nicd barrel cell..

And while you're at it, a piggy back 2MB chip mod. :-)

Last edited by Jope; 03 April 2015 at 10:47.
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Old 03 April 2015, 17:48   #5
kipper2k
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Quote:
Originally Posted by Jope View Post
The jumpers can be cross referenced from any of the big pictures of a500+ boards on bboah with the aid of the schematics. This is less than 7/10 in difficulty imo. :-)

Perhaps I'm weird, but I'd populate the clock too, perhaps with a coin cell. The clock isn't wretched, it's the nicd barrel cell..

And while you're at it, a piggy back 2MB chip mod. :-)
The 7/10 is for the desoldering process, too much heat will damage the tracks feeding the ram chips, No need for the piggybacking when you can use the 1mb expansion board. One issue also is the height of the chips in the sockets, the new RAM chips in the sockets will make them a little too high and they will interfere with the keyboard laying on top so you have 2 choices, no sockets, or grind down the lower end of the chips to allow for clearance.

For the clock circuit there are quite a few components that would need to be added, i thought about it and figured the less modification in this case, the better
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Old 03 April 2015, 19:39   #6
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Yeh, since you're doing a 1MB with clock, the situation is a bit different.. I was thinking mainly if you had the board and wanted to scrape together an a500+ without buying that many extra parts.

The clock bits can probably be scavenged off some 512k ram expansion, most use the commodore circuit. :-)

But sure, I wouldn't recommend this as someone's first soldering job.
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Old 04 April 2015, 00:13   #7
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I did this once by scavenging some compatible memory chips from old Virge card (not sure if it was that or even if it was PCI or VGA) but didn't bother adding new caps ?

Or were those surface mounted that you had to put on ?

Anyway it worked as planned before I gave it away so I hope I didn't do wrong by not recapping it ???

Also , with no PSU I modified ATX psu connector and soldered it to board directly so PSUs can be exchanged so it should be well supplied with power.

I hope the guy can play SWOS on it still
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Old 04 April 2015, 00:52   #8
kipper2k
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Quote:
Originally Posted by blizz1220 View Post
I did this once by scavenging some compatible memory chips from old Virge card (not sure if it was that or even if it was PCI or VGA) but didn't bother adding new caps ?

Or were those surface mounted that you had to put on ?

Anyway it worked as planned before I gave it away so I hope I didn't do wrong by not recapping it ???

Also , with no PSU I modified ATX psu connector and soldered it to board directly so PSUs can be exchanged so it should be well supplied with power.

I hope the guy can play SWOS on it still
The caps were just an extra i done due to the original caps sitting upright preventing an addon cpu board from sitting flat
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Old 04 April 2015, 01:03   #9
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Ah I see smart move
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Old 04 April 2015, 11:43   #10
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Originally Posted by kipper2k View Post
The caps were just an extra i done due to the original caps sitting upright preventing an addon cpu board from sitting flat
Majsta hasn't got around to shrinking the Vampire 500 down to the size of a 68000 DIP socket just yet. I think the pitch on the tiny FPGAs put him off or maybe it's the other IC's
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Old 04 April 2015, 23:24   #11
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Waiting on tutorial! good work Kipper as usual!
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Old 05 April 2015, 05:08   #12
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tutorial added to post 1, if you need clarification on anything, let me know
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Old 05 April 2015, 08:10   #13
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Nice stuff. Do you want me to move your tutorial post under one of the stickies in support.hardware?

On second thought, I'll just stick it here.
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Old 05 April 2015, 14:36   #14
kipper2k
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Nice stuff. Do you want me to move your tutorial post under one of the stickies in support.hardware?

On second thought, I'll just stick it here.
Excellent. Thanks
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Old 06 April 2015, 00:29   #15
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Kipper - can you PM me the price for parts and delivery to UK? ... also will the Amiga recognise as A500 or A500+ following this or is there no difference from that perspective other than hardware upgrade difference between the two? I've also got 512K trapdoor RAM in my A500 at the moment. Will this conflict with the internal RAM upgrade or will it provide me with even more RAM!?
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Old 06 April 2015, 01:00   #16
kipper2k
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Originally Posted by lesta_smsc View Post
Kipper - can you PM me the price for parts and delivery to UK? ... also will the Amiga recognise as A500 or A500+ following this or is there no difference from that perspective other than hardware upgrade difference between the two? I've also got 512K trapdoor RAM in my A500 at the moment. Will this conflict with the internal RAM upgrade or will it provide me with even more RAM!?
Hi,

Your Amiga will be a basic a500+ with 1mb chipmem and no onboard RTC. putting in a 512k trapdoor mem expansion will add 512k chipmem to bring it to 1.5mb. The max chipmem you can have is 2mb, 1mb onboard and 1mb in trapdoor.

I'll check out prices and post them for you. Mailing to UK (and most parts of Europe) is $8 USD small packet air
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Old 06 April 2015, 01:08   #17
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Hi,

Your Amiga will be a basic a500+ with 1mb chipmem and no onboard RTC. putting in a 512k trapdoor mem expansion will add 512k chipmem to bring it to 1.5mb. The max chipmem you can have is 2mb, 1mb onboard and 1mb in trapdoor.

I'll check out prices and post them for you. Mailing to UK (and most parts of Europe) is $8 USD small packet air
Cool thank you!

Also will there be any problems in using the stock Kickstart 1.3 in this system? I have an EEPROM programmer but I'm not sure if it will allow writing onto existing Kickstart ROM?
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Old 06 April 2015, 08:57   #18
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Also will there be any problems in using the stock Kickstart 1.3 in this system?
No problem.

Quote:
I have an EEPROM programmer but I'm not sure if it will allow writing onto existing Kickstart ROM?
No, ROMs are immutable.
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Old 06 April 2015, 10:37   #19
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Thank you for all information guys.

I think i'll I try to convert my Amiga 500 Rev.8 on my own when i get some time.
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Old 09 April 2015, 14:46   #20
kipper2k
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Baby needed a new home so i made it one





click for supersized

and the back view...




click for supersized


I haven't screwed it down yet, it needs at least 7 days to cure

Last edited by kipper2k; 09 April 2015 at 14:58.
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