A500 green screen

[rockstar]

I've just bought a used Amiga 500, which was supposed to be working. However, when I power it up, it gives me a green screen and the power LED blinks (a cycle of 10 short blinks and then 1 long). It had been pretty carelessly packed, so that it would move around in the box quite a bit if shaken or dropped, which it most likely has been.

I've tried a number of things to no avail:

· Removed the RAM expansion and replacing it with one known to be working.

· Lifted and reseated all chips (Fat Agnus, the two CIA's, Denise, Paula, Gary, the ROM) except the CPU.

· Cleaned the motherboard with isopropyl alcohol (although it seemed to be in excellent condition).

When turned on for a couple of hours, the CPU, Denise, Paula, Fat Agnus and the two CIA's become warm. The RAM chips, the ROM and Gary remain "cold".

I know that a green screen officially means that something is wrong with the chip RAM, but I read somewhere that it might as well mean that something is wrong somewhere on the data bus. Does the fact that some of the chips remain cold indicate an error on one of the buses?

Any suggestions?

[_ThEcRoW]

The green screen usually appears when one of the chips of the chip ram is faulty. If you can verify that in your miggy, then you will need to find new ram chips to replace. A interesting source of this kind of chips is the old isa pc video cards. These usually have 1mb, and you could replace them. I heard of a guy that upgraded his 500 with 1mb chip, just adding 512k from one of these cards to the empty sockets of the a500 and adding the needed capacitors.
Hope this help.

[rockstar]

Interesting! How do I verify that I have a faulty RAM chip? As I said, none of them get warm after leaving the power on for a couple of hours.

I'll start looking for old video cards at work, then.

[zipper]

Perhaps it's not your problem, but I got green screen with a bad contact of Agnus, with a cracked socket. A tie wrap and superglue did cure it.

[drbytes]

How do I verify that I have a faulty RAM chip?

Verifying ram chips is a bit difficult exept if one gets very hot or stays cold (while others warm up). But if your amiga was supposed to be working before sending it to you then i would expect a loose contact in one of the custom chips. I saw green screens often which were caused by a bad contact from the agnus chip. So maybe check the Agnus (again) to be sure. Also what you can try is to exchange the CIA's in case one of them is causing the problem. First off all you should try the amiga without the expansion ram board and only replace it when the amiga is working again (then you know for sure the ram board is not causing any trouble.) If possible try another powersupply and if all fails then maybe its best to replace the ram chips with sockets and find some other ram chips to test the amiga with.

I'm not sure if the ram chips should get warm or not in the A500 but if you can measure if the chips get power (5v) then i guess the temperature is allright.

Good luck!

Tom

[Markus_Bieler]

Green screen means faulty chipram.

But it doesn't tell you which part.

1. check Agnus (?wrong agnus inside?) dead agnus
2. Soemone tried to make the 1MB hack and did it wrong.
3. one of the ramchips is dead.

It woulkd be beter to know the rev. of your board.  I'll try to find some hints.

[glitch]

Perhaps the 1MB chip RAM modification has been done and an older Agnus is in place?  Check for cuts to the traces around where the RAM expansion is located.  That being said, is there still an A501 (or workalike) inside of the trap door?

Good luck!