Ami_Junki's a500 & a1200 Cap replacement.

[r0jaws]

Ami_Junki was looking for someone in the UK to check over his machines and replace the Caps. I volunteered and am going to use this thread to document my progress.

Firstly the package, just the original box wrapped in a bin liner. Both machines inside were well wrapped in bubble wrap and in good shape though.

The 500 fires up to the 1.3 kickstart screen, so all working fine.

A check of the general condition shows it's in pretty good shape on the outside, minimal yellowing.

On taking it apart there appears to be some sort of residue all over the keyboard plate, I'll be giving that a clean up later.

Stripping it down to the motherboard reveals that there are no nasty surprises, it all seems in order and Ami_Junki gets on and orders a set of capacitors for a Rev 6a motherboard from Cosmo on his thread.

These turned up this morning and it was time to get going. The capacitors are as follows:

location, original, replacement
c303, 22uf 35v, 22uf 63v
c304, 22uf 35v, 22uf 63v
c306, 10uf 35v, 10uf 50v
c307, 470uf 16v, 470uf 16v
c324, 22uf 35v, 22uf 63v
c334, 22uf 35v, 22uf 63v
c401, 3300uf 10v, 3300uf 10v
c402, 3300uf 10v, 3300uf 10v
c712, 10uf 35v, 10uf 50v
c811, 100uf 16v, 100uf 35v
c812, 100uf 16v, 100uf 35v
c813, 100uf 16v, 100uf 35v
c814, 100uf 16v, 100uf 35v
c815, 100uf 16v, 100uf 35v
c816, 100uf 16v, 100uf 35v
c821, 47uf 16v, 47uf 50v
c822, 47uf 16v, 47uf 50v

I removed the original caps, using snips at first and then generous amounts of flux and hot air was called in to finish off the job. This is a time consuming job, as they are connected to the ground which acts as a giant heatsink so patience is a must.

With all the caps removed it was time to solder in the replacements. If you're doing this yourself, take care to check the polarity. Put them in place, and then check again before soldering. The polarity is marked on the motherboard which is very useful. Again this took a bit of time, but you can't really rush this job.

Once they were all in place and soldered, it was time to clean up and check that we still have a working system.

That is a result, and once I reassemble the whole machine I shall give it a full work out and make sure there are no problems.

Once she is fully re-assembled and tested, it will be time to start on the 1200.

 

[Zetr0]

Great work buddy!

Seems all that GameGear and ninty DS repairs have payed off

 

[johnim]

nice work mate

 

[ChrisUnionNJ]

And another amiga comes back to life!!

 

[TheCorfiot]

Simply Excellent

 

[BrooksterMax]

Wow Phil, great work and craftsmanship. You really are a Mr-Fix-It

Are you sure you were not a Service Engineer?

Thanks for taking pics too, nice to see work in progress

 

[merlinkv]

Hi my friend

Nice job!!!

You can post pics of desoldering proccess?

Sorry for this noob question but I want to do the same in one spare A4000D board.....

Thanks

Hi again, my friend... Not needed I found a lot of tutos.... I will start practics with some spare boards first.....

My best wishes as allways.

 

[Allen1]

That's an excellent job Phil, I've changed surface mount caps as on 1200's with hot air but not thru hole ones as on the 500. For the 4 thru hole caps on the 1200, I use my Pace desoldering station which melts the solder and sucks it out, I know TC uses hot air to strip or replace parts too but I haven't tried it myself just yet but I will try your method out next time.

The 1200's are easier to strip in comparison, the main problem is the plastic parts of the audio connectors and the keyboard connectors as they can start to melt when you use the hot air to remove the caps. I used some thin metal shields cut from an old CD drive to protect various plastic parts where the heat could affect them (PCMCIA slot, IDE, Keyboard, audio and floppy power connectors).

When soldering in the new caps on the 1200, especially the two between the audio and keyboard connector, it might pay to use those shields to protect against the soldering iron catching or coming close to the plastics as I found out when I was doing the first one oh: nothing to serious but it could have been.

Good luck with the second machine, you would have probably known about shielding the plastic parts but I mentioned it as a reminder and mainly to help anyone else who is thinking about changing their caps and to avoid melting certain parts.

Looking forward to the 1200 cap replacement post

 

[Merlin]

Very nice work, Phil! I think you need to receive a Level 3 Solder Tech certificate from Zetr0 for that job...

 

[Zetr0]

Very nice work, Phil! I think you need to receive a Level 3 Solder Tech certificate from Zetr0 for that job...

moist assuredly when he does the A1200, the cert is in the post!

 

[merlinkv]

As I said a nice, clean and professional job!

Waiting for the A1200....

 

[r0jaws]

@merlinkv,
The desoldering process was quite simple, just time consuming.
If possible, snip the cap off and then flip the board over. I found it much easier to remove them from the other side.
I use plenty of flux, and set the hot air at about 250deg and air 2 or 3 and set about warming the area thoroughly. After about 3 minutes, I'd increase the heat to about 300deg and It sometimes helped to use the iron at the same time to concentrate the heat on the weld.
I then used a standard solder sucker to remove the solder, and generally that would take a few goes.
Big heatsinks like these can be a problem and frustrating, but patience really does pay off. Don't forget to keep the air moving around, it can blister and damage PCBs really quickly if left in place too long.

@Allen1
The shielding is a very good point, I used it on a couple of caps as they were close to some components, but generally I find that working from the underside helps a great deal with that.

All of these techniques I learnt under the patient tuition of zetr0 (cheers buddy), but practice really does make perfect.

 

[r0jaws]

Update time.
I finished off the 1200 yesterday. SMD components require as much patience and care as their through hole counterparts although you must use the hot air to heat both sides equally to remove them without damaging the tracks.
First I fired it up to check it was working Ok..

The plastics are in pretty good shape, with minimal yellowing and only one dimple from a case screw in the bottom left corner.

I removed the motherboard and it started to prep up for the removal.
I had the caps ready for replacement:

location, original, replacement
c214, 10uf 25v, 10uf 35v
c235, 100uf 6v, 100uf 16v
c236, 100uf 6v, 100uf 16v
c237, 470uf 16v, 470uf 16v
c239, 100uf 6v, 100uf 16v
c303, 22uf 25v, 22uf 35v
c304, 22uf 25v, 22uf 35v
c305, 10uf 25v, 10uf 35v
c307, 470uf 16v, 470uf 16v
c324, 22uf 25v, 22uf 50v non-polarised
c331, 22uf 25v, 22uf 50v non-polarised
c407, 10uf 35v, 10uf 50v
c408, 1000uf 10v, 1000uf 16v
c409, 100uf 6v, 100uf 16v
c459, 22uf 25v, 22uf 16v
c811, 1000uf 10v, 1000uf 10v
c821, 47uf 16v, 47uf 16v
c822, 47uf 16v, 47uf 16v

Cosmos had originally supplied some 22uf, 35v SMDs to replace the audio channels on c324 & c331 but I used some non-polarised 50v replacements.

The through hole caps were pretty straight forward, but the SMD caps can obviously only be removed from the top with hot air. This means plenty of shielding is required to protect the surrounding plastics. As Allen1 mentioned earlier, the audio caps are next to the keyboard socket and the audio sockets so particular care has to be taken.

With patience all the caps were successfully removed, there was one casualty however.

The composite out socket distorted. I had put some shielding on, but whilst heating the through hole cap from the underside, it melted to the shielding. I was using rather a lot of heat, as this cap was attached to the ground right next to the RF housing which was acting as a heatsink again, and obviously it was too much. Fortunately the damage is purely cosmetic, and the output works fine. I wasn't very pleased though.

All the other caps, including the tricky audio ones were removed and I started to prep for the replacement. I removed all the existing solder and tinned the surfaces in readiness.

The first caps I replace were the audio ones. Cosmos' pack of caps had included some 22uf 35v to replace the original 22uf 25v. However these were polarised, I decided that whilst they would work I would install some non-polarised ones. I got hold of some, but they were not SMD, so I simply trimmed the legs and bent them at right angles before soldering them directly onto the pads.

The rest all went back on with no further dramas and I made sure all the welds were good and buzzed out the continuities.

I fired her up for a test, and she sprang to life.

Happy that she at leasts starts with no problems, I connected the floppy drive and started up Chuck Rock II. I played for about 10 minutes and everything ran smoothly, including the sound.

We are planning on retro-briting all the plastics in the next couple of weeks, so once that's done it will be re-assembled and off on it's way home again.

 

[Cosmos]

Very good... Think about removing the dust with a paintbrush !

 

[r0jaws]

Very good... Think about removing the dust with a paintbrush !

Don't worry about that, she'll be thoroughly cleaned before reassembly.
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[Allen1]

That's a great job Phil and I still haven't tackled removing a thru hole component with the hot air station yet, one day I will definitely give it a go

A good desoldering station is maybe something to add to your arsenal for future projects as its localised heat from the tip directly to the via and component and makes things a lot easier in many cases. Mind you its still possible to overheat components just like all the other options but they do make life that much easier when replacing parts especially where large ground planes are involved.

All the best,
Allen

 

[Zetr0]

@r0jaws

Some fine work my friend!


@Allen1

I use an Aoyoue 474 Int. Solder Sucker, as well as the Kada 852D+ Hot Air Rework Station - it certainly allows more room to plan an attack - some of them ground plans are monsteriously huge!

 

[r0jaws]

Having seen zetr0 go to work with his desoldering station it is definitely on my shopping list.
It makes the process 100% easier, maybe Christmas.

 

[Allen1]

Wow that Aoyue 474 looks good, I use is an old Pace MBT-100E which has a similar desoldering iron to the one I used at work a few years ago. I also like the Kada 852D+, my hot air station doesn't have a temperature readout so its a bit more trial and error till you get used to it (but they are still very handy).

Phil its not far off Xmas now, so its about the right time to be dropping hints to family and friends

All the best,

Allen

 

[r0jaws]

I was pretty annoyed with myself for damaging Timo's 1200 and I don't like to do a shoddy job so I had to do something about it.
I bought replacement socket and set about removing the old one.

It's a tough job as again the ground is an absolute pain, but with a lot of persistence and a ton of flux I soon had the old one out.

It didn't take long to solder the new part in, and it was then just a case of cleaning her up ready to test.

Because I used a different type of flux I had to clean the board with a solution of screen wash and water. She is currently in my hot press drying out thoroughly before I test her.
However, I buzzed out the continuities and everything is tickety boo so I'm confident she will be fine.
Once she is ready I'll put her through her paces and post pics.