If you own an Amiga, especially an A4000, read this!

[patrik]

Stumbled upon a page which describes why the sound of the A4000 eventually will die and what to do about it:

Amiga Audio Circuit Capacitor Repair

On the same site I also found a page describing a construction miss of the A3640 CPU-card which result in serious damage to the A3640 in time:

Amiga A3640 CPU Board Repair

Happy soldering!


/Patrik

[odin]

:nervous:

[bloodline]

odin wrote:
:nervous:

I'd rather get Someone like Dave Hayney to check this out before I start poking my hot iron in my Amiga.

[Karlos]

I'm sure Dave Haynie would tell you a reverse polarised capacitor is a bad thing ;-)

If it's obvious that said capacitors tend to leak after a while, and those same capacitors were reverse mounted, its a no-brainer, really ;-)

[patrik]

@bloodline:

Measured the voltages supplied these to capacitors  of my rev3.1 A3640 and they were indeed reversed as in the article.


/Patrik

[bloodline]

patrik wrote:
@bloodline:

Measured the voltages supplied these to capacitors  of my rev3.1 A3640 and they were indeed reversed as in the article.


/Patrik

I have no doubt of that, the A3640 is no masterpeice of engineering... but I'm concerned about the Audio caps... that's got me worried.

[patrik]

@bloodline:

Inspect the area around them and see if you see any oily substance on the motherboard itself. If there is a substance like that present it should be removed and the capacitors replaced as soon as possible to prevent damage to the motherboard and nearby circuits. The capacitors are the two inside the red circle of the picture below:



(edit): Propanol (I am not sure if that is also the english word for it) is good to use as pcb cleaner as it will absolutely not damage the protective coating of the pcb.


/Patrik

[Acill]

Hmmm, where are these audio caps on an A3000? I have a service manual and could look for them. It would help if they got pointed out to me though. I would hate to have to poke in my A3000 again with a soldering iron!. I've done it before though.

[MrZammler]

Damn, could that be why my A3640 has died... ?

[amigamad]

I never knew this sure is nice to know. :-)  :-o

[HopperJF]

so many fantastic benefits of using an "old " computer.
there has been years for people to find ways to fix even the silliest and most crucial of things for it:)

[patrik]

@Acill:

They should be located near the audio-connectors and they probably have a capacitance of 22uF as that was their rating also in the A500 when I checked now.

Though I think that you are quite safe with the A3000. Those capacitors are in all amigas subjected to these reverse voltages under certain conditions. This is not healthy to any polarised capacitor, but the capacitors in the A4000 seems to be of especially low quality and very prone to leakage.

(edit): It is never a bad thing to have those capacitors replaced with non-polarised capacitors though.

(more edit):

Checked a bit in the A3000 service manual and it should be the capacitors named C433 and C443 (named exactly the same as those in A4000). These two are the ones inside the red circle in the image below:



@MrZammler:

Not impossible, if you examine the areas of the A3640 near the capacitors for leakage you can see if that was the reason. Not impossible to fix it either. The guide in the link I posted is quite detailed on how to try to fix it.


/Patrik

[redrumloa]

Very good stuff!

[x56h34]

I've known all the time about the capacitor issue in A4000 (the #1 cause for bad sound or no sound at all in A4000), however I've been told by a friend who was a huge Amiga geek/repair guy back in the day that they simply dry out. Never heard of any leakage.

edit:

So what I am saying is that as long as you've replaced or removed the Ni-Cd battery from your A4000 motherboard you are probably safe from any further damage. The dry capacitors will not cause any harm, but only make your sound dead, and even this won't happen right away but you will notice it slowly degrading through time, until you replace the capacitors with more advanced quality ones.

[Acill]

Thanks for the info. I found them on my A3000. They look like they are in good shape still. I have perfect sound, and its mixed through my sound card too. If I ever loos the Paula sound I know what to do and look for.