HELP! My Amiga 4000 isn't working!

[Thomas]

As always, please, look at the power LED first. All colors on the screen do mean nothing if the power LED does not behave normal.

The power LED should go on with half its brightness after power-on and about half a second later it should switch to its full brightness. If it does not do this, the computer does not work at all. Usually caused by a loose or defective processor board.

If it becomes brighter ok, then it should blink about ten times while the screen shows the error color. Then the computer resets and all starts over again. And again and again.

If the power LED does not blink and the computer does not reset after ten flashes, the colors do not have any meaning. Because the first thing the Kickstart does is to switch the power LED bright. If it does not come past this point, the processor does not work and without the processor, there is nobody who could switch colors.

I cannot tell you anything else than the others: to remove the motherboard from the case, remove any periphals and try it alone. Just plug in the processor, the LEDs, the monitor and the power supply. Then switch it on and watch the power LED. And the screen. Easiest way to test the blink/color+reset mechanism is to remove the chip RAM. Without chip RAM the screen should become green immediately (after the power LED has become brighter). After the power LED has flashed ten times, the screen should go black for a short time and all should start again.

Bye,
Thomas

[Thomas]

The power LED is the main health indicator of any Amiga computer. On the early models (A500, A2000) the LED was completely controlled by the processor (i.e. it stayed completely dark until the Kickstart switched it on) and on the later models (A500+, A1200, A4000) only the brightness is controlled by the Kickstart. The power LED is also directly connected to the low-pass sound filter. So if some music program switches off the sound filter, the power LED becomes dark/dimmed, either.

Given that the not correctly working power LED has something to do with the problem and assuming that the crashes are caused by random interrupts, I would guess that one of the CIAs is dead.

Unfortunately on the A4000 most chips are soldered to the motherboard. On an A500 you could easily swap the CIAs in order to test it.

Another point to look at is the power connector on the mother board. People have reported that over time some of the wires burn out, indicated by the insulation becoming black. Perhaps, if one of the wires has a loose contact now, it would cause random crashes, too.

Bye,
Thomas