a500+ repair help needed

[chsedge]

I got today an old a500+ not working.

I tried at home with a power supply of mine and a 520unit to get the video signal out of the rf connector.

I powered it on and get nothing, only black screen. I tried to swap something from another a500 like the 68000 and the fat agnus but nothing again. Drive doesn't click or search for anything. The green led remain stable even after the power on.

Have you any suggestions? What should I check in first place?

The power supply and drive are perfectly working from another a500.

thanks

[blobrana]

Hum,
assuming that video signal out is working..
The computer goes through a list of `selfchecks` during the 'boot':

      1. It clears old data in RAM
      2. Disable DMA and interrupts
      3. Clear the screen
      4. Check hardware (ie, is the 680x0 working?)
      5. [color=000099]Change screen color indicating pass/fail[/color]...
      6. Perform checksum test of all ROMs
      7. Change screen color indicating pass/fail

   
Looks like it happens before the Change screen color ...

[BoingBoss]

Unplug the 520 unit and plug a standard video cable into the composite out RCA jack on the rear of the A500.  Plug the other end of the video cable into the video-in on your TV.  Turn on the Amiga 500.  You should see a b/w screen.  If not, try changing the Denise chip.  There is a good chance that the Video Hybrid IC, near the Denise chip is bad.  If something is plugged into or unplugged from the RGB port while the Amiga 500 is on then the Video Hybrid IC will be damaged and must be replaced.  They are very hard to find.  I sell new Commodore Video Hybrid ICs for only $24.95 each or used ones for $15.00 each.   :-)

[chsedge]

I tried also that but I also get a black screen. Also tried to replace denise chip. I think it's the video ic as you told. But explain me this, if this is broken the boot process can't get finished? that is why the floppy doesn't click?

excuse me for my bad english, I'd like to know if this causes to the amiga to stop before doing the initial check of the hardware

And also another question, is this video hybrid done by resistors only, can I replace it with some of them? Is there any circuit or data available?

bye