Resistor for Amiga 500 Plus Repair?

[Big Supes]

Hi guys,

I'm currently repairing an Amiga 500 Plus that is suffering from a black screen. The battery has leaked onto the motherboard, but luckily it hasn't done too much damage.

For the moment I have found a resistor that has badly corroded legs that needs replacing. To be precise, it is C12 as shown in the picture.



Any ideas where I can source a replacement?

Thanks

Adam

[talybont]

For Rev 8 motherboard, that is a 10nF capacitor.

http://www2.mouser.com/ProductDetail...73gOujIKkvgJQJ

[Big Supes]

Originally Posted by talybont

For Rev 8 motherboard, that is a 10nF capacitor.

http://www2.mouser.com/ProductDetail...73gOujIKkvgJQJ

talybont, you're a gentleman. Thanks very much!

[Big Supes]

Will this work: http://uk.rs-online.com/web/p/cerami...itors/5381196/ ??

The link above was 9p for the capacitor and £12.90 for delivery!!

[talybont]

It should work, or this:

http://uk.rs-online.com/web/p/cerami...itors/5373454/

[talybont]

But I think your motherboard probably have more problems than just that cap. Most likely there are some traces that have been broken from the battery leakage. I would check all the traces in that area for continuity.

http://beta.amigapcb.org/ is a great tool in this regard.

[kipper2k]

Hi,

That capacitor missing or corroded is highly unlikely to be causing a black screen unless it is shorted out. I cant see the surrounding area to see what other corrosion there is but chances are it is somewhere on the data bus, Gary socket is a good place to start, remove Gary chip, check to see if the pins are green and clean as required, also Agnus should be pulled and reseated, careful though, after years of sitting there you run the risk of breaking the socket if not careful.

[demolition]

Yes, that capacitor is just a supply decoupling capacitor for U12 and board should very likely run fine even if you remove it. It is also not important if you replace it with another 10nF cap or use 22/47/100nF instead. Whatever you can find.

[Big Supes]

Thanks for the feedback guys, it's much appreciated. To be honest, I thought I'd get this capacitor changed and then go from there. I've taken out all the main chips and pushed them back in, but no joy.

Once the capacitor has been changed, I'll update this thread as any help would be appreciated.

[fordav1]

the "corrosion" is almost zero compared to most A500+'s I've seen.
unless the green stuff is shorting out 2 traces/pads, that small amount of corrosion won't stop it working. I've seen much worse that were working fine.
Check for broken tracks in the area. If none, I've fixed a few A500+'s.... in a lot of the cases it was one of the 74LS244 buffers (U12 or U10) and/or one of the traces going to or coming from those chips. Amigapcb.org is the way to go. sit there and trace each pin and you'll find the problem. The 244's could also just be bad, have seen that a few times too, one of the 244's just failed for some unknown reason. I've used that site a few times to great success. A couple of weeks ago I sat down with a dead Amiga 1200 that had leaky caps and 4 days worth of tracing later and a few wires patches and it was running :-)
Also remember it can be a bad chip. Swap the CIA's as a start, then the other custom chips from a working machine.

[Big Supes]

Quick update, the board is getting power through it although it seems Gary and one of the CIA chips is dead. To buy these individually, it almost costs as much as a working Amiga 500 so I'm not really sure what to do with it.

Sent from my SM-G950F using Tapatalk

I would check for continuity/shorts from the battery area to Gary and the Even CIA. Far more likely to be a damaged trace than both chips blowing.

[Daedalus]

Very common is for the Gary socket to be corroded. Take the Gary chip out, and if you find that the terminals are corroded, replace the socket. A couple of traces also run through the battery area to Gary as already mentioned, if they're damaged you'll also get a black screen.

[Big Supes]

Thanks for the suggestions guys, I will do all the above.

Sent from my SM-G950F using Tapatalk

[turrican9]

Originally Posted by demolition

Yes, that capacitor is just a supply decoupling capacitor for U12 and board should very likely run fine even if you remove it. It is also not important if you replace it with another 10nF cap or use 22/47/100nF instead. Whatever you can find.

So I could replace it with a 0.1uF (should equal to 100nf) electrolyte radial as long as I get positive and negative leads correctly?

[demolition]

Originally Posted by turrican9

So I could replace it with a 0.1uF (should equal to 100nf) electrolyte radial as long as I get positive and negative leads correctly?

Electrolyte caps may not all be suitable for decoupling but the worst that could happen is that it has no real function (which is most likely not a problem). Just remove the old cap and leave it like that. A single missing decoupling cap is very unlikely to cause any problems.

[turrican9]

Originally Posted by demolition

Electrolyte caps may not all be suitable for decoupling but the worst that could happen is that it has no real function (which is most likely not a problem). Just remove the old cap and leave it like that. A single missing decoupling cap is very unlikely to cause any problems.

Thanks for your feedback. I bought a working A500 plus motherboard a few months back. Traces was still corroded and legs of U12. I cleaned everything up with vingear and fiberglass pen.

Lately I removed U12 to inspect under it. The backside of the legs was corroded and a few dark spots on a couple of the traces that run under it. In the process of putting in a socket and replacing U12 with a new one. Seems to me this chip better be removed after a batterty leakage. At least when it's legs are corroded. I'm sure it would have worked fine for a long time but sockets and these chips are cheap from China anyway.