Amiga 1200 boot problem

[jkg]

Hi all Amiga doctors

So.... it's time to ask for some... uhmm.....what was the word again........help? Ok, I'll admit that I find it hard to do so when I really decided to do it on my own

I've tried for quite a while now to fix a broken 1200 motherboard.. just for learning and having fun.

Now here's what I've done and the result so far:

After replacing capacitors and fixing 4 broken connections on the underside (corroded) I now get the kickstart screen (3.0). I can also get to the "quick boot option menu" and move the mouse around - but I can't boot from neither ide/sd (works in another 1200) or the floppy drive. It just clicks and wont load if I insert a floppy. (Again, this works on the other Amiga. ) On bootup I often get Software error 8000 0001 Task 0000 2720

One obvious (?) thing to try is to swap kickstarts with the working machine.

Also I guess there can be more broken traces. Is it possible to get some ideas from the schematics for this "specific" problem? It's a revision 2B btw.

Do you have any other ideas on what I could try?

[supaduper]

Could be a ram prob, have you a ram expansion card you could borrow ? and see if it is the ram cos obviously with the extra ram it will boot.
Just throwing a suggestion at you, I had An A600 that would show the WB screen but not boot added a 1mb ram card and it booted, it was one of the ram chips was bad

[jkg]

First, many thanks for the response I tried to insert a 4 mb (Blizzard 1200) but there was no change (but it was recognized in quick boot menu).

Then I tested the kickstart chips in my working A1200 and found that they're OK. Then I installed the kickstarts from the working machine into the one I'm trying to fix and voila - the software error seems to be gone :-)

However I still can't boot - neither from floppy nor from IDE. My theory for the moment is that the even CIA (U8) may be broken or that it doesn't receive some signal that it needs.

[jkg]

Today I found that I was missing a connection between pin 11 on u37 to ROMOE (goes to kickstart). I got it to boot by just bridging E113R on the back with a piece of wire. Now the 1200 finally boots off the sd card.. cheers for my first Amiga repair! I guess I've been quite lucky with the board since it only had broken traces etc.

According to the schematic (http://www.amigawiki.org/dnl/schematics/A1200_R2.pdf) it seems like it should be a resistor and a capacitor on E113 - but I dont have any. Can anyone tell what value the resistor should be? I'm not sure what */68 means.. but it seems like most other resistors have 680 written on them. I'm also confused since I've seen one picture (backside of rev 2b) on the net where it seems like only the capacitor was fitted...

Can anyone enlighten me please?

[voyager_1701e]

The 68 in the schematic does mean 68 ohms.....on an SMD resistor 680 means 68 ohms....681 would mean 680 ohms...682 6.8k ohms (6800 ohms) etc

The E113 in the schematic appears to be a 68pf capacitor as you said and the 68 ohm resistor doesn't have its part number marked but they are E112R E113R and E114R on the board. E112R/C E113R/C and E114R/C seems to be the same. Typical Commodore I guess!

I just checked a 2B board I have here...Indeed the E112R E114R are fitted to my board as 68R, ie 68 ohm resistors. E113R is not fitted and doesnt look like it ever was. E112C -114C are all fitted.

Good work on your repairs so far!