Dead A1200

[DarkXavier]

Hi
Just been given a 1200 thats not working. Will not power up at all, the power supply is humming so I expect its probably working. Never used an Amiga before so I'm stuck. Any ideas?

Thanks

Rich

[Daedalus]

Well, first things first, does the power light come on on the machine at all? Second, does it get brighter after a couple of seconds and stay bright? Third, does anything come up on the screen when you try it? Solid colours or anything?

[DarkXavier]

Nothing at all. I stripped the machine down to see if anything was touching the motherboard but it looked ok. The metal shielding has been butchered around where the HDD mounting is. Just checked the power supply with a multitester and its fine.

[Daedalus]

Hmmm... There has to be something serious wrong for the power light not to come on at all. Did you check the solder pads around the power supply connector? Perhaps it's been abused... Or maybe a burnt trace carrying power, should be fairly obvious if it's on the top or bottom layers. If you're handy with a multimeter, the schematics are available, and you might carefully check for the presence of +5V and +12V at key points (e.g. floppy connector, filtering capacitors etc.)

Edit: Of course, if you haven't done so already, you'll need to remove the shielding altogether. Anti-static precautions and usual disclaimers etc...

[DarkXavier]

Just checked for power on the board. There is power at the cpu slot and the floppy drive and also the video port @ 12 volts. But where there is meant to be 5 volts eg the mouse ports there is only 0.5 volts??

[delshay]

plug the a1200 into a monitor/tv a may be just a faulty led.

[tone007]

Could just be the 5V on the power supply is gone if you haven't checked that yet, there should be 5V at the floppy power as well.

[DarkXavier]

There is 5v showing at the power supply. There isn't 5v showing at the floppy power.

[spaceman88]

There is 5v showing at the power supply. There isn't 5v showing at the floppy power.

I have seen A1200 schematics on the internet, you'll need to download one and start following the 5V line. Also check for a poor connection on the power input and check for low resistance to ground (with power disconnected!!) on the 5V line. Are any IC's getting warm?

[mikolas]

I had exactly the same problem and the problem was a burnt line on the back of the motherboard. Check out around E561C (near serial connector) and C311-C314. There should obviously be some visible damage, but it is pretty easy to fix by soldering some wire to bypass the damage. Also, on the front side of the motherboard, check next to RAM chips.

I got this damage by shorting 12v/5v lines when fiddling around to power a 3.5" hard drive from floppy power and as the end result lost 5v supply (or it was around .5v). As someone has toyed with the hard drive mounting area, I suspect you should follow this path to floppy power connector.

If there's no visible damage, then it's time consuming multimeter work awaiting.

Mikko.

[delshay]

you can power a A1200 motherboard though the floppy connector only just to see if it works.