Wednesday, March 07, 2018

Yet Another A500+ Motherboard - Finale

Only two parts to this one. This is because the board is actually in pretty good condition overall. There are a couple of things.

First, the missing pads at JP7A and J9. Just to be absolutely clear, the pads were loose when I got the board. They were also like that when the previous owner got the board. Fortunately, I was on hand to sort that out with a hot metal stick and some de-solder braid and a solder sucker. Poof! They're gone! The loss of these isn't critical but does mean certain modifications would be a bit more tricky in future...

Next, the dodgy ROM. It's dead. It's expired and gone to meet its maker. It's bereft of life. It's shuffled off its mortal coil. It is an ex-ROM. I stripped down my own A500+ and nicked the ROM from that for a few tests. It went straight to the familiar boot screen with no problems. This meant I could plug in an external drive and test it with that rather than stripping down my A500+ any further. And test it I did. I ran the Frontier game demo and just left it for a few hours. No problems.

“Don’t cry because it’s over, smile because it happened.”

Next, the joystick and mouse ports had pins broken. I'm certain that one pin was missing from the joystick port when I got the board but I'm fairly sure I broke off a couple more with my incessant waggling of the mouse plug trying to get it out. Oops. As luck would have it, I have a big bag of connectors that I 'over ordered' a while ago. They're not as good quality as the originals but they fit, they work and I have plenty....

Broken ports - oh dear. :(

The first thing to do with the old ports is, rather obviously, remove them. This was a bit of a pain but not as bad as I expected. With lots of de-solder pump action, some input from de-solder braid and a lot of patience they were eventually persuaded to come out. The hardest bit is the two anchor pins which provide mechanical stability to the ports when they're on the board. The solder joints are rather large and needed a much hotter iron than normal as well as lots of suction and a big waggle to get them to release. They both came out with no damage to the board though which was a good result.

Joystick Port Removed

Mouse Port Removed

Next, I had to solder in the new ones. This was surprisingly easy. After cleaning the board thoroughly with isopropyl alcohol and cotton buds, they just slotted straight in. I soldered one corner pin first while holding it firmly to the board, then did the opposite corner. This held the thing place while I did the rest. The larger joints for the supports were also fairly simple and just needed a hotter iron and a lot (a LOT) of solder to fill the holes. Rinse and repeat.

New ports loveliness
And from the back..

I'm really pleased with how the ports turned out and the only way you can tell they're not original is because the hex screws are a different thread to the originals. This was something I only realised as I was putting them in. Oh well. You can't have everything. A quick check with the standard Amiga test disk (courtesy of Kier on the Amiga Facebook group) proved that they are working correctly.

The final repair was to the cluster of resistors and diodes in the AUDIO FILTER section of the board. The pad on the underside of the board had been destroyed so the leg of the resistor and diode was just sticking through the hole.

Pad gone - leg with no connection
To repair this I took a piece of kynar wire and threaded it through the hole. I made sure it was long enough to extend along the leg of the diode on the other side.

Kynar wire in place - to be trimmed once soldered
I carefully soldered the wire along the exposed track, making sure that wire also joined nicely to the leg of the resistor. The I turned the board over and soldered the other end to the leg of the resistor/diode combo. Finally, I trimmed off the excess wire on the underside.

Repair complete on this side

Repair complete on underside of board

And that's about it. I did a final test to check that the audio filter still works (it does) and that I hadn't broken anything else (I hadn't that I could see). Pending the acquisition of a 2.04 ROM, it currently has KS1.3 installed. Another A500+ motherboard saved and almost ready to be released back into the wild. Thanks for reading. :)