problem with an amiga 1200 motherboard

[whitebird]

Hi all,

I bought a second hand A1200 board but it seems not to be working.

There are no peripherals connected to the board (no keyboard, no floppy drive, nothing just power supply)

When I turn on the power, a black screen appears and is displayed during a few seconds then the system seems to reboot and I see again this black screen and so on and so on...

So I decided to check the roms. I made a little electronics circuit with a 16F84 PIC. This circuit reads the ROMS and sends the data to a PC. When memory dump ended, I had a 512K rom file on my PC which I tested with Winuae, but all is working well... So ROMS are OK.

What is the reason of this bug?? Is it because there is no floppy drive connected?? Is it mandatory to have this device attached to the board during boot up??

Thank you in helping me.

[Smiley]

No its not mandatory to have a floppy drive attached

[whitebird]

OK so it is just a little monger to boot?

[whitebird]

sorry a little longer

[Parsec]

Can you test it with a different power supply?

[RetroMan]

Without IDE HD the A1200 can take up to 30 seconds for booting up ...

[whitebird]

Parsec, I have no other power supply but I know the one I have is not faulty because it works with other amigas.

I really don't know what is wrong with this board. The fact that it reboots periodically looks like a software related problem. Perhaps rams are bad or there is a cpu heating up problem (bad CPU). But the problem can be custom chip related.

Where can I find information about custom chips chronograms and in general repair tips for the amiga 1200?

[DDNI]

You didnt say whether there was an expansion card in the trapdoor slot.
If there is try the A1200 without it.

[whitebird]

No, there isn't any expansion board attached.

[Overdoc]

Hard to say, but the fact that it stays black and reeboots is typical for a bad CIA or a trapdoor expansion problem, at least on A-500s.
Anyway it would be interesting to see how the power led is doing (blinking ?!), and if the diskdrive would be reacting in some way ?
Also, have you tried holding down both mouse buttons when switching it on to get into the startup-mode ?

[whitebird]

What you are saying is interesting Overdoc. I'll try to connect some LED's and try to see if I can enter the startup mode. I'll also try to connect a floppy drive to see how it behaves

Thanx

[whitebird]

I had a more carefull look to the board and noticed one PCB track is broken! It's the track between Alice's pin n°4 and Lisa's pin n°64 (on the DRD bus) I don't know what's the purpose of this bus but it probably helps the system in working correctly when it's connected :-) I didn't repair it yet, but I'll try it very soon

Someone knows what the DRD(31-0) bus is??

[whitebird]

I finally solved the problem which was due to the broken track as described in my previous message.

[keropi]

very nice!!!! congrats!

[whitebird]

Thanks Keropi

[Parsec]

Originally Posted by whitebird

I finally solved the problem which was due to the broken track as described in my previous message.

Well done - you should offer a repair service with skills like that! Might make u a few quid too

[amethyst]

Originally Posted by whitebird

Someone knows what the DRD(31-0) bus is??

It's the DRAM Data bus lines

[whitebird]

Well done - you should offer a repair service with skills like that! Might make u a few quid too

In fact the big challenge was to repair the track directly on the PCB rather than adding a long wire between Alice and Lisa. So I had to insert a very short wire in an area were the tracks are very close one of the other.

It's the DRAM Data bus lines

Thanks