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ScuzzBlog: Diaries January 2019

Entry 13th January 2019: Post 01: Amiga 500 - Will not be number 6


Amiga 500 - Will not be number 6
If you read my blog from a few days ago you will appreciate that
I discovered an issue with an A500 that is housed in an A500Plus
case. For some reason the mouse just jumps from the bottom to tops
of icons making it impossible to click them. So I wanted to fix
this. Sadly when I connected the computer up I had even worse a
problem. She wouldn't boot, the floppy was dead and I had a solid
yellow and green on the LED lights. Never mind.

My first challenge was to uncover a load of suitable chips. The
A500 uses the older OCS chips and the A500Plus the ECS chips or
enhanced chips. I have five broken A500Plus motherboards which
I show here with the ECS chips. I did some research and it seems
I can use the ECS chips. So I looked for a suitable donor.

Each defective board was numbered and I have identified the
various problems that made the boards unusable. I know one had
been left in a wet damp garage for years and was in a dreadful
state when she arrived here. I managed to replace the board.

My problems just got from bad to worse as the very first chip
I extracted to check had a broken/damaged socket pin. It looked
like it had been crushed. No idea how long it had been like that.
I have labelled the motherboard six on the photographs and I
really do hope she doesn't become Number 6 of broken boards.

Having assembled my chips I just had to wing it. Both the CPU
and ROM were changed to the 500Plus chips and I just kept my
fingers crossed the CPU would work in the broken slot.

So next I swapped out the GARY. That was a success as the A500
now booted into the start up screen. The floppy was still broken
but the yellow light went out. I then rummaged through my bits
and bobs tub and found a couple of floppy drives. I hooked up
an A2000 floppy and magically the computer sprang to life. Sadly
still with the jumping mouse issue.

So I swapped out the PAULA but that made no difference. Having
read up on mouse issues I had decided it wasn't a CIA so I left
them alone. So one last chance to get the computer going. And so
I turned to DENISE and swapped her out.... THAT WORKED. It worked.
She now had full mouse operation. The computer was holding steady
and she operated, it would seem with no problems.

So I quickly hooked up a less than pretty internal A500 floppy
and gave the workings a good clean. I then reinstated all the
internal workings, shielding, screws and expansion memory in the
trapdoor. She was alive and ticking no problem. I was amazed. So
the A500 got an ECS makeover and she is alive.

Sometimes you get a load of luck mucking around with computers.
I know that there are many that literally jump straight in as a
capacitor issue, but I never do that. It really is the very last
thing that I consider. What amazes me is that I am generally
right in my hunches. I had already reseated the DENISE cus I was
convinced it was that chip causing the issue. I only went ESC cus
at first it was the only 500 chip I didn't have. That is why I
pulled all those motherboards out. I'm glad I did.

Happy days. Here are pictures of the 500 in the PLUS case. Also
images of the five broken boards. I would love to get those boards
working, but I haven't got keyboards and cases anyway. I hate that
they are broken. But as long as they can breathe life into my other
computers then they are still very important.

Cuppa me thinks. And that was a very long day.

Amiga 500 - Will not be number 6

My A500Plus graveyard.

Five very sad A500Plus motherboards.

The A500+ motherboard.

Memory chips.

2.04 ROM.. Half moon at the top.

68000 CPU half moon at the bottom.

The very Fat Agnus.

DENISE handles graphics.

Odd CIA for serial, parallel, joystick & mouse ports.

Even CIA for serial, parallel, joystick & mouse ports.

Nasty gunge.. not by Commodore.

GARY or gate array chip.

PAULA Amiga's native audio plus floppy control.

U15 may be causing the mouse issue.

Battery killer on the A500Plus.

Always check for corrosion at U12
and U13 and the expansion pins. Also
GARY tends to take a hammering.

Note the white residue everywhere.

Corrosion on those pins and the socket will be shot.

Spot the green to chip pibs.

I numbered the five boards with
the main board killer faults.

The battery damage isn't too bad here.

Missing socket seat from ROM chip.

Missing pins from AGNUS socket.

Missing socket pin receivers from ROM.

Missing and corroded pins to AGNUS.

Battery plague.

Corrosion to GARY.

Chip removed and socket is shot.

Sadly my latest victim .

Pin socket close up. May still work.

Assembled spare chips ready for usage.

Problem with 500 as the lights are solid
and I have no floppy working.

Replaced GARY and hooked up a 2000 floppy.

May look a bit odd but did the trick.

OK so we have a working Amiga 500.

Sadly still have the problem with the mouse.

So I set too swapping out all the chips.

DENISE was the last to get changed.

I also upgraded to ECS using A500Plus chips.

AND SHE WORKS... It was DENISE all along.

Boots no problem.

Reconnected the RAM card.

And salvaged an old floppy drive.

The joy of putting the computer back together again.

Just the trapdoor to go.

And a scribbled note to say what I did.
Named the computer DENISE.

Power up and disk at the ready

And there she goes.. WHOO HOOO !!!

All working and no stuttering mouse.

And I upgraded to ECS. Such a clever girl.

Expanded chip memory.

And the keyboard was working just fine.

So DENISE did not become number 6.

I never doubted it for one minute


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Last updated 13th January 2019

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