A500 Won't Recognize 3.1 ROM

[jammarob]

Howdy!

I'm running into a strange issue with my Rev 5 Amiga 500. I can't seem to get it to boot from a 3.1 ROM (black screen). The EPROM has been modified as required to work in a rev 5 motherboard.

The system will boot to it's stock 1.3 kickstart with no issues. Here is what I have tried:

*EPROM tested in another Amiga 500 and works.
*Reseated all socketed ICs.
*Replaced CPU with known good CPU.
*Tried a different 3.1 ROM that is also tested as good.

Here is the keyboard LED error code I see:
https://www.youtube.com/watch?v=gBcCypJiNSc

If both mouse buttons are clicked to enter the menu, it loads part of the menu and then freezes:



I am at a loss. Any ideas? I don't recognize the keyboard error either

[jammarob]

I actually bought both EPROMs from Amigakit, and this particular A500 will not boot to either, but the EPROMs work on another Rev 5 A500.

I can only get this particular Amiga to work with its stock 1.3 KS ROM

[jammarob]

I don't want to do that because the EPROMs work fine in a different rev 5 Amiga. I don't think the issue is with the 3.1 ROMs themselves.

[jammarob]

I have done that already

[jammarob]

Good tip. I'll check continuity between the pins of the EPROM and the socket.

No funky switchers here. Just trying it straight in the board!

[jammarob]

The modification to the 3.1 ROM (mentioned here) addresses the issue with the larger ROM. It's almost as if it's not bank switching, but only reading part of the ROM data. The incomplete startup menu is really strange.

I have tried it both with and without the Commodore 512K expansion with the same results.

[jammarob]

Continuity checks ok.

I'm stumped.

At this point I think i'll just pick up another A500

[jammarob]

That is very helpful, thanks for that!

I'll get a hold of a logic probe and oscillator this weekend and start poking around the CPU.

It's certainly possible that one of these resistor packs could be faulty.

[jammarob]

**UPDATE**

I couldn't figure out this revision 5 A500, so I picked up a revision 6A A500 from a local electronics junk store today.

None of the 10-pin resistor packs mentioned earlier are populated on this board. It would NOT recognize the 3.1 kickstart EPROM until I populated RP107 with a 9 x 47K resistor pack.

It now recognizes the kickstart and boots, but adding an A508IDE causes it to become unstable.

Does anyone have the values for RP106, RP108, RP110 on a revision 6A?

[jammarob]

Yep! Unfortunately, they are about to permanently close. Everything is 80% off, so the A500 was pretty cheap.

https://www.youtube.com/watch?v=AIy__NX9SvQ

[jammarob]

FIXED!

Adding the resistors to RP106 and RP107 fixed the initial issue with stability, but adding the A508IDE caused software crashes to return.

I replaced the CPU with an HCMOS part (Hitachi HD68HC000P8, but any 68HC000 part should work). Every NMOS CPU I tried experienced the same software crashes. Sucks I won't be able to use a 68010, but it does me no good if it doesn't work at all.

Thanks for all of the help fellas! I hope this thread can help other people try to resolve similar issues.