Amiga 1200 motherboard to save!

[flaviosr]

Hi to All,

I am not a technician so, before making "stupid" errors, I would like to have some ideas from experienced people.
I have an Amiga 1200 mobo that does not work.
The screen simply remains black (there is an output since the monitor gets something) and the floppy drive doesn't make any noise.
When I received the mobo one of the two kickstart chips, the 391523-1, was reversed but aligned with the 391524-1.
I was thinking about recapping the mobo but this could take a lot of time without a good final result.
Do you have any suggestion? Could the reversed chip have damaged "something"?

Thank you

[CodePoet]

Hi,

I don't think anything was killed by having one of the Kickstart roms backwards. It may short Address line A0 with A16 and *potentially* pull A18 high (all of which can halt bootup), but the symptom of this should be a red screen and not a black screen.

The fact that you received it with the rom backwards suggests the user trying to fix an existing (possibly non rom-related) fault

Edit: Have you tried booting with the ROMs removed?

[flaviosr]

Edit: Have you tried booting with the ROMs removed?

Without the kickstart I would have never thought about doing this...
What have I to expect?

[hese7]

If the motherboard was turned on when the Kickstart chip was installed reversed, the VCC (+5V power) was fed to the chip's ground pin and probably broke the chip. When you put the chip back in correct orientation and turn the computer on, you probably either get a red or black screen, depending on how bad the Kickstart chip was damaged.

Without the kickstart I would have never thought about doing this...
What have I to expect?

You will only get a black screen. The computer doesn't show anything on the screen or click the floppy drive if there is no Kickstart installed.

[flaviosr]

If the motherboard was turned on when the Kickstart chip was installed reversed, the VCC (+5V power) was fed to the chip's ground pin and probably broke the chip. When you put the chip back in correct orientation and turn the computer on, you probably either get a red or black screen, depending on how bad the Kickstart chip was damaged.



You will only get a black screen. The computer doesn't show anything on the screen or click the floppy drive if there is no Kickstart installed.

So the issue is that it could be that one chip is damaged. It would be great.
And I am full of kickstart 3.0 chips when I changed from 3.0 to 3.1 in my other Amiga 1200...
I am going to try with other kick and I let you know the results...

[Chucky]

First of all..  everyone is sayinh "screen is black" but ALWAY ALWAYS *ALWAYS* forgets the interesting thing:

POWERLED!  does it change brightness after aprox 1 sec?  if not something hold the machine not able to start the kickstart..

recapping will NOT make a nonbooting A1200 start!.  
I repeat:

RECAPPING WILL NOT MAKE A NONBOOTING A1200 START.

ok with this said..

your kickstartroms MIGHT have been damaged if turned the wrong way.   if in wrong postition the only thing that willhappen is the machine be dead.
so try to get hold of another set of kickstartroms.. (or.. my DiagROM) and test

[Chucky]

Hi,

Edit: Have you tried booting with the ROMs removed?

Ehh? that would just end up in a machine with black screen, no powerled change.  simply. DEAD..

[LoadWB]

Ehh? that would just end up in a machine with black screen, no powerled change.  simply. DEAD..

I think the point was to reproduce the behavior.  If the system behaved the same with and without the KS ROMs then the ROMs could be suspect.

The LED change is a good point to reference.

[flaviosr]

Ok. Done some more tests.
The green led (the only one that turns on) do not flicker, it remains steady.
I tried 3 other Kickstart sets and nothing changes.
The behaviour is always the same (black screen and steady green led).
Somewhere I also have a set of 3.1 Kickstart set but I cannot remember were... I am going to look for it in the next days.
Anyway I do not think that ALL the 3 3.0 kickstart sets have died in these not usage years!
I have also tried without the Kickstart chips and the behaviour is the same with or without them, so the issue should be (according to what I have read) that the Amiga cannot pass the control to Kickstart... am I right?
I am quite sad. I am afraid that the possibility to repair the mobo is beyond my capabilities... I am not capable of testing electrical parts understanding what's happening or desoldering and soldering chips...

One more thing: I removed the FDD so all my tests have been done without it, but I do not think it can change the situation (obiously the first tests were done WITH the FDD connected!).

[Oldsmobile_Mike]

This is a dumb question and you probably already tried, but -- a different power supply?

[scuzzb494]

Hi to All,

I am not a technician so, before making "stupid" errors, I would like to have some ideas from experienced people.
I have an Amiga 1200 mobo that does not work.
The screen simply remains black (there is an output since the monitor gets something) and the floppy drive doesn't make any noise.
When I received the mobo one of the two kickstart chips, the 391523-1, was reversed but aligned with the 391524-1.
I was thinking about recapping the mobo but this could take a lot of time without a good final result.
Do you have any suggestion? Could the reversed chip have damaged "something"?

Thank you

Can be useful having as much information about the board as possible. Very useful also to have some high res pics to look and see if any work was done to the board in a past life. Could be something simple. Checking the tracks would help just on continuity no power. My guess is that its fried but who knows. Like I say some pics would be good.

I've had black screens for all kinds of reasons. Means nothing really.. just that it's not working. Shame.... All is not lost though.

By the way... leave it on for a good while. Safely. What is getting warm ?

[Chucky]

Next thing is to grab an oscilloscope and test if you have all clocks.
also multimeter to check if all adress and data-lines works.

ONCE a dead machine started when plugging in an accelerator card for me. but that's only once..

[mastersetter]

Ok. Done some more tests.
The green led (the only one that turns on) do not flicker, it remains steady.
I tried 3 other Kickstart sets and nothing changes.
The behaviour is always the same (black screen and steady green led).
Somewhere I also have a set of 3.1 Kickstart set but I cannot remember were... I am going to look for it in the next days.
Anyway I do not think that ALL the 3 3.0 kickstart sets have died in these not usage years!
I have also tried without the Kickstart chips and the behaviour is the same with or without them, so the issue should be (according to what I have read) that the Amiga cannot pass the control to Kickstart... am I right?
I am quite sad. I am afraid that the possibility to repair the mobo is beyond my capabilities... I am not capable of testing electrical parts understanding what's happening or desoldering and soldering chips...

One more thing: I removed the FDD so all my tests have been done without it, but I do not think it can change the situation (obiously the first tests were done WITH the FDD connected!).

 Sure you have loads of amigas and a1200's, it's not the end of the world if it doesn't work anymore first world problems..

[flaviosr]

Dear All,

thank you for your help.
I am using the "Great Warrior PSU", the one that I use when I make tests... trying anyway with a different one didn't changed the result! Obviously these PSUs are working with other Amigas! I also checked the V at at the connector (for example, checking a Commodore 128 PSU connector I discovered that it is bad! :-o).
I tried with kickstart 3.1 and nothing happened. I didn't expect anything different but I wanted to try.
I tried "touching" the main chips and I do not feel differences in temperature. (or perhaps I do not want? :-( ...) Anyway they are soldered so I would not be able to change them.
I am not going on in further analysis. I am simply limited by my capabilities on making repairs...
In the future I hope to find somebody that is able to repair the mobo! The complete Amiga (without FDD) is safely stored!

[Castellen]

I am not going on in further analysis. I am simply limited by my capabilities on making repairs...
In the future I hope to find somebody that is able to repair the mobo! The complete Amiga (without FDD) is safely stored!

I could provide a long complex list of things to check, but without the right equipment and knowledge, I fear you'd be stuck at step 1.

Depending on where you're based, there are various individuals providing repairs.  I offer comprehensive hardware fault tracing and component level repairs from worldwide.  Sending an A1200 main board to NZ is fairly cost effective.  Email me for further details.

Else see the forums for other repair services.