Amiga 600 smoking - Help!!

[mamejay]

Hey everyone,
pulled out my Amiga 600 tonight to fit a new CF card adapter.
I tried to get it started and all I was getting was a grey screen.
I just left it on for about a minute and then I noticed some smoke coming from under the floppy drive.
Immediately switched it off and removed the floppy drive. Found a component labelled 1R0. I suspect this is a resister but I am not 100% sure.
What does everyone think? What is it and is my miggy repairable?

 

[Collz69]

Have you tried those Nicorette Patches?
or
maybe the gum?


sorry, I couldnt resist

 

[demolition]

Did you remove the CF adapter and try again?

R309 is a 1 ohm supply resistor for the audio reference voltage circuit. Even though it looks bad, it probably still works fine, however something else is causing it to heat up. Something must have shorted on its secondary side to cause that current. It could be a wire or clipping on the PCB (blow it clean), C307, C3 or U3 primarily. Also check the cables for the floppy drive if they have been damaged and could have been touching the MB.

 

[mamejay]

Did you remove the CF adapter and try again?

R309 is a 1 ohm supply resistor for the audio reference voltage circuit. Even though it looks bad, it probably still works fine, however something else is causing it to heat up. Something must have shorted on its secondary side to cause that current. It could be a wire or clipping on the PCB (blow it clean), C307, C3 or U3 primarily. Also check the cables for the floppy drive if they have been damaged and could have been touching the MB.

Thanks so much for that. Getting late here so will look at it tomorrow with some fresh eyes. If I do need to replace that resistor can I just use a standard one or do I need somthing special?

 

[r0jaws]

You can check if the resistor is still functional with a multimeter using the continuity check function.
But primarily you should be trying to find the cause of this fault. Make sure that everything is disconnected including the floppy drive and that the motherboard is clean and free of debris, both sides then try starting it up with just the power and video output connected.
It will take a little longer to start, not having a keyboard or floppy hooked up, but it will give you a better idea of what maybe the fault.

 

[mamejay]

You can check if the resistor is still functional with a multimeter using the continuity check function.
But primarily you should be trying to find the cause of this fault. Make sure that everything is disconnected including the floppy drive and that the motherboard is clean and free of debris, both sides then try starting it up with just the power and video output connected.
It will take a little longer to start, not having a keyboard or floppy hooked up, but it will give you a better idea of what maybe the fault.

Resistor is showing 3 ohms on my meter. I removed everything and tried the bare motherboard on the table with power and av but no display. Just a grey screen. Everything else look nice and clean with no damage. Not sure even when to start looking for this one

 

[roy_bates]

look for bridged traces around the op amp,or bridges in general.
you would need to short out the motherboard to do that to that resistor.

check your power supply is ok as well if its the original supply,i dont think its healthy for a supply to take that much strain.

 

[demolition]

Resistor is showing 3 ohms on my meter. I removed everything and tried the bare motherboard on the table with power and av but no display. Just a grey screen. Everything else look nice and clean with no damage. Not sure even when to start looking for this one

Try shorting the pins on your meter just to see what 0 ohm actually measures like. It is not uncommon the the leads to have up to 1 ohm in
resistance, which would have to be subtracted from your measurement.

If you have the equipment for it, you could try removing the 1 ohm resistor altogether to see if that breaks the short. The Amiga will boot without it, just with broken sound. But as roy_bates writes, the problem lies somewhere else, not in the resistor itself. The hot resistor is just a symptom.

You can replace it with another 1 ohm resistor, however it should be one of the same size or the power handling will not be high enough.

Does any of the caps I mentioned get hot as well? If they do, then that is probably where the fault is.

 

[mamejay]

Not that I can see. I was thinking of recapping the board and doing what I can before handing it over to someone look at for me.

 

[rkauer]

The 1 Ohm resistor is actually a fusistor (resistor + fuse) and its role in a circuit is to break if something shorts out.

A damaged fusistor tells the circuit after it have a serious problem, be it a short-circuit caused by a metal touching the traces or a bad capacitor or a dead chip.

The Amiga will boot without the pre-amplifier section, but not if Paula is dead.

 

[mamejay]

Anyway of testing if Paula is dead using a scope or otherwise?

 

[mamejay]

OK. Found this article about fixing a A600 with a similar issues to my one.
http://mutantcaterpillar.wordpress.com/2012/07/21/the-amiga-600-and-the-unusual-suspects/

Started going through it and the CPU Halt was held low so I started looking at the Gayle chip.
I replaced capacitor C611 and fired up the amiga. I was checking the output line of the 555 chip which was showing 3.4V. I nearly gave up when the voltage dropped to zero and my kickstart screen appeared! Success.
My miggy is back from the dead!!

 

[WonkeyDonkey]

Good to see another one is spared a one way ticket to Amiga heaven