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Old 16 January 2017, 18:12   #7
Pat the Cat

Join Date: Dec 2016
Location: Nottingham, UK
Posts: 481
Originally Posted by trixster View Post
I'll give that a try, but why do I only get the green screen with the Mediator board installed, and not when the original zorro board is in?
The self tests the Amiga does first thing are a little bit slapdash and hurried.

To test the chipRAM, the processor tries to write a few values out to the chipRAM, testing the bits and the address access. It doesn't test the whole lot. It then tries to read the values back, and if the values are wrong, it warns there is a problem with accessing chip RAM.

So, a green screen can be a bad RAM chip, but can also be a problem with the databus being scrambled by something.

My guess is, the Mediator wasn't burn tested - you are supposed to leave electronics running for 24 hours or more, to make sure that the components do actually work with consistently under load. This is not easy to do properly unless you have LOTS of A4000s to test on.

However, even if it was burn tested like that, a component could still have failed in the meantime, and is now scrambling the databus when the Mediator is plugged in.

My 0.02 cents worth - that's a LOT of expansion for a desktop Amiga. Checking power rails is pretty much measuring with a multimeter, checking that voltages are corect (5 volts really is within 10% of 5V, and not 6V or 4V). You do that with the PSU unplugged, so you CAN'T damage the Amiga while doing it. Checking voltages is usually enough to tell if a PSU is dying. Pros will do things like, ideally, measuring with the board plugged in - to see if the voltage drop caused by powering the device is bringing the system down, or whether the PSU is chunky and butch enough to supply the amps needed. Don't try measuring amps unless you have a very robust multimeter, and the experience to use it properly.

Multimeters are very cheap nowaday, even extortionate places like Maplin stock them for less than £15. Also very handy for checking fuses without plugging them in. So it is worth getting one just for checking voltages and resistance. Don't go into measuring amps unless you really understand power rails.

The logic chips on A3/A4 Amigas daughterboards are not too tricky to find. They are generic components, not custom chips like Agnus. So if there's a problem there too, it should not be too much of a bother to fix.

It's a pain in the behind for you in the meantime, but it's all fixable.

Last edited by Pat the Cat; 17 January 2017 at 00:27.
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