It's Still Awesome - And Now It's Complete!

Brand New A500+ Part 2

It's nice to have new things. A new phone, a new shirt, even a new pair of budgie smugglers (urgh!). It's even nicer when the new thing you have is high quality and better than what you had before. And the A500++ board is very high quality and better than the original in several ways.

First, and most obviously, it's brand new with no Varta acid death and is very good quality - gold plated contacts and a shiny purple finish. Almost too nice to solder anything to.

A Thing of Beauty

Next, any A500+ owner will know that there is an annoying fudge near the 'Audio Filter' section of the board where a diode is soldered at an odd angle. It's a factory mod that corrects a cock-up in the board that was obviously too costly to correct. It stayed that way for the (short) life of the A500+. But the purple beauty solves that issue too.

Other useful things to know are that it has a space for header pins to allow the selection of internal or external drives being connected as DF0, handy for all you Gotek'ers out there. And, best of all, the silkscreen includes many more details not included on the original, of both the component values and also including a subtle nod to the plight of the most vulnerable custom chip when Varta spews forth its poison. 'Poor Gary' indeed.

Improved Silk Screen. :)

Back to my board. One thing I mentioned in the first part was that I was intending to complete this project with as little expense as possible by a) using anything that I had 'in stock' already and b) de-soldering anything else from the donor board. Large items like the power socket, video socket etc are a given. But then there are lots and lots of passive components (resistors, capacitors etc) as well as logic chips and other ICs that I could buy brand new, but the cost of this could quickly add up.

As luck would have it, I had a little bonus from work, and I'd treated myself to a Duratool de-soldering workstation from CPC Farnell just a few weeks ago. And I am glad I did. If you plan to do anything like this, you really should consider getting one of these or something similar. De-soldering a few hundred component legs using a manual pump or de-solder braid would  have taken months. The tool itself is a soldering iron with a hollow core that links to an air pump so, when solder is heated, pressing the trigger activates the pump which sucks the solder into the glass container on the de-soldering gun. I have to tell you now, it took a beating during this project.

That'll need a clean...

Removing components with the tool still took some time. My initial runs with the de-solder gun resulted in many blockages and frustrating delays as I had to keep clearing the glass chamber and the small metal pipe that runs from the tip of the gun into the body. After a while I got quite adept at removing the glass, spring and filter almost one handed, and the delays became fewer and shorter. Some components still required the assistance of a soldering iron to allow their removal. This took a toll on the tips of my iron and I ended up replacing it twice during the removal phase..

That'll need a replacement...

At the back of the main board there is a long row of what looks like ceramic capacitors. They look like that because, in actual fact, they ARE ceramic capacitors but each one has three legs. They are a specific type of cap that (I have to be honest) I had not seen before, known as Feedthrough Capacitors, designed to have an almost ideal insertion loss apparently. Ahem. In any case, removing these took a significant amount of time as they got very, very hot, even with a very small dwell time on the legs. Heat does not do these components any good and I did actually end up with the centre leg of one cap just falling off, and another one nearly splitting in two. The one with the gammy leg was replaced by a willing volunteer from an old Rev6 board I have. Despite this, I managed to get pretty much everything de-soldered without too many problems other than my lack of patience. :)

Some items that I fitted to the new board I did eventually cheat on, and some, as mentioned, I already had. New items I either bought or already had were:

• New IC sockets* - essential when the custom chips have been removed from a battery damaged board
• New resistors - I'd intended to use the old ones but then realised how cheap they were and relented
• New ceramic caps - I already had a box of various values (expect 330nf) so used these
• New electrolytic caps - already had them all in stock from previous repairs :)

*I didn't have a socket big enough for the CPU so I de-soldered the old one and removed the manky pins. Then I removed shiny new pins from some of the new sockets I had and inserted them into the old socket. I've done this before and it's lots of fun (no it isn't).

Shiny new pins for the CPU

Everything else came from the original A500+ board.

Box 'o bits (one of several)

In all I spent about £10 on new sockets and resistors. Note that to aid future maintenance, every chip got a socket, including the Video Hybrid. This socket was made from slicing a bigger socket in half. :)

Almost done stripping the donor..

The following sequence of pictures shows the steady progression over a couple of weeks....

So, after about three weeks of component swapping, finger burning, de-soldering station unblocking fun, I ended up with this:

Finished! Yay!

Would it work first time?

No.

First test. Board appeared completely dead. I'd forgotten to plug the power supply into the wall.

Second test. Keyboard light stays dim. No display output at all. Then I realised I'd left the Video Hybrid chip unplugged (doh!).

Video Hybrid (the tall thin dude near the back)

Third test. Green screen followed by reset. Bugger.

At least with a green screen, something was happening and it indicated that the system was trying to start up. So, back to diagnosing green screens and an Amiga.... My immediate suspicion was on chips U10, U11, U12 and U13. These are the ones that normally take a big hit from Varta and frequently need to be replaced. I started by swapping them out one by one. Sure enough, the last one I swapped at U13 solved the issue. The SN74LS373 at that location had died, and with a new one the board booted but with an odd colour tinge.

Hmmm. Not quite right...

It was obvious there was a colour problem. In fact, all blue was missing from the image. After a bit of jiggling of the Video Hybrid and other chips I tried again. This time I was missing blue AND green. Everything was red. Dammit.

I removed the modulator and tried the built in composite output which is just black and white but it was crystal clear. So I plugged the modulator back in and tried again. This time I had all the right colours and ended up at the familiar purple boot screen. Yes!

What had happened was that the video socket that was harvested from the old board had acquired a healthy dollop of flux on its pins. Wiggling the modulator in and out a couple of times removed it allowing a full connection and the correct colours to be displayed. Nice.

Ahh! That's better!

So, next test. I plugged in my trusty AlfaPower external hard drive.

Old Faithful!

Would it work?

Success!

Yes. Yes it does work.

Now all I need to do is pop it in the case and everything will be fine.

     Or will it? (hint - it wasn't)

To be continued.....