Amiga 1200 doesnt power on, but power light blinks when given power

[Changis]

I got a a1200 that was supposed to work, but when i try to power it on, i only get a green LED flash and nothing more, black screen.
I've checked the caps and everyone seems to be in order, i have however just gotten a recap set from amigakit, but will wait until i get my new smd hot air station and/or until i hopefully get some more clarification on what to do.

I've changed the through mounted ones just to see if that helped, but no change.

I've looked over the motherboard and cannot find any obvious fault and all parts and solders look fine

(I am using a modified ATX powersupply from an old computer that has more than enough to power everything)

Does anyone have any suggestions?
The board rev. Is 2b
I also have a 1d4 i can use for parts as some idiot tried to remove the factory timing fix and burnt off two pads and managed to pull a trace up from the pcb a cm or two
(Which is annoying because this was a working board, and the one i got it from was just trying to change the resistor with a new one, without proper equipment or solder skills

I will try to get some photos from both boards when i have the opportunity

Hope somebody has some ideas

[supaduper]

First off reseat the two socketed Kickstart roms may just be a bad connection

[indigolemon]

And might be worth trying to get your hands on a Diagrom set too

[Sim085]

Originally Posted by Changis

(I am using a modified ATX powersupply from an old computer that has more than enough to power everything)

This could be your problem. I had similar problems where after putting an accelerator card in the A1200 it sometimes booted, sometimes didn't (similar behavior like yours), sometimes restarted continuesly, i.e. - tries to boot and restarts, etc.

When I asked here they pointed out how the ATX power supply does not work like the Amiga power supply and sometimes it does not give enough power to the A1200 because there is not enough load on it (#14 in linked thread).

Check voltage on the +5V and +12V lines to see if enough power is coming from the power unit.

Here is the thread I had started; http://eab.abime.net/showthread.php?t=88887

[Changis]

Update:
Dismantled the amiga and rf shield

Removed kickstarts, cleaned sockets with electronic contact cleaner

Reseated kickstarts

Photographed motherboard and searched for faults (easier to do when you can zoom in)

Found water damage around some chips

Cleaned corrosion as good as possible with isopropanol and electronic contact cleaner
It seems three contacts on one chip may be bad, i'm assuming this is the reason the amiga won't start.. have to wait for my air soldering station.
(Does anyone know what chips these are?)

A question:
Is it possible to interchange parts from one 1200 to another? (I have a rev 1d4 with some broken traces that i might make a new inquery about here if anyone here is fairly knowledgable in pcb layouts to fix broken/missing solder pads)

I have provided some pics, for easy uploads and ability to keep full picture sizes, i will host them on google drive (link in bottom of post)

Quote:
Originally Posted by Changis View Post
(I am using a modified ATX powersupply from an old computer that has more than enough to power everything)
This could be your problem.

This power supply runs fine on another amiga 1200 with 1220 accelerator card and a converted laptop hdd, so powering it with this psu should be no issue. I also tested it with only LEDs attached and no keyboard, floppy, accelerator card, and got no change. But as stated above, i do believe the issue is the corrosion that occured

Pics will be hosted here:
Google Share

[lesta_smsc]

You could check out : http://www.amigapcb.org/

May be worth following tracks that appear damaged and re-route them. You can use chips from donor A1200 but possibility of getting both working if done right...

[Changis]

Originally Posted by lesta_smsc

You could check out : http://www.amigapcb.org/

May be worth following tracks that appear damaged and re-route them. You can use chips from donor A1200 but possibility of getting both working if done right...

Thanks alot.. now i can possibly have 2 working a1200, thanks

[Changis]

Quick update:

I managed to get a simple powersupply to test with, and lo and behold, it now stayed on, nothing more, but it stays on now

anyway, i don't seem to be able to get any output from it.. though this is most likely the corroded area..


regarding the 1d4 with a broken trace; with the help of amigapcb, i was able to rectify the resistor fix that was broken using alternative pads, however, i think the rgb port may be bad on this, if i manhandle it a little, i get blips of purple screen (i'm assuming the insert disk screen is showing) but i cannot get a stable picture.. i went over the rgb-to-scart cable and resoldered and tested the cables, and it seems fine, it just seems like the rgb connector or trace under might be bad.. i desoldered and resoldered the rgb connector, and no change

I currently don't have a viable option to test with composite, as im using a scart to hdmi converter (it has worked with amiga 1200 before with this cable)
EDIT: i found a rca-to-scart to try composite with.. it seems the 1d4 gives a video signal when powered on, it gives some faint purplish static lines before going black, but it still seems to be keeping a signal.
the 2b does not show any change other than maybe a blink in the signal, but it does not seem to be keeping the signal (this board will be retested after i get my smd station and can fix the chips properly.

can the problem lie somewhere else? it seems like it would be a loose rgb connector the way it behaves, but i've had the connector off the board, and manually soldered it back, so could it be a bad trace?

[Changis]

Update 2: finally got my hot air station and took off and cleaned the corroded chip, one trace wasnt working so i just wired it up directly. I also removed the pcmcia slot as i wont be using it, and some unreachable contacts were corroded to the point they wouldnt really melt the tin properly, so i figured it was better to remove it completely than try to salvage it at this point. If i need one in the future, ill try to get a replacement port to solder back in

Atleast some progress was made, i now get a "signal" when hooking it up to a display, however, the display is just grey with short black lines scrambling on the screen. I get this both on RGB and composite..

i tried searching for similar issues, but only found ones that pointed to CXA1145 (which i understands converts rgb to composite and rf, so rgb should work if it was cxa1145 at fault, but composite and rgb gives identical scrambled static as descrived above, it seems to me maybe the the graphics chip ot something? Any hwlp would be greatly appreceated