A600 repair advice

[BennehBoy]

Another forum member very kindly gifted me an A600.

This machine had probably not seen any use for quite a number of years.

The PSU tested OK so I powered it up to find it working (I could load Amiga Test Kit from floppy), however after a few power cycles this changed and the machine was then black screening.

Opening up the lid I got the very familiar fishy smell of electrolyte, closer inspection of the board showed that many of the solder joints around the aluminium caps were very dark & corroded.

After ordering a quality recap kit I set about removing the failed components from the board - this proved to be incredibly difficult, despite using lots of liquid flux none of the cap legs wanted to take solder or release from the board with any ease, judicious but careful cleaning didn't help, a lot of the silk screening simply crumbled off - perhaps due to electrolytic corrosion?

I used a lot of good quality flux and gradually lifted alternate sides of each cap using my micro soldering iron. Unfortunately this last resulted in having 3 caps with 1 of their 2 pads completely lifted.

2 problem ones next to the IDE connector look fairly straightforward to reroute using kynar, but I wonder if anyone has a good solution for C304, the pad for this via's to the other side of the board but I can't see where the trace ends up due to the silk screening (it's in the region of R347 & R346).

This is a rev 1.5 board btw, and I also hear that the schematics may not be correct for the caps on this side?

You can see the level of corrosion from the photos, but to be honest I think the level of faffing due to the components not wanting to budge helped me end up with the broken pads, they were fibre pencilled, scrubbed with IPA, plastered in flux, and had fresh 0.4mm solder applied all with no luck, so it became a bit of a struggle. I've no hot air here, and with retrospect would use that in future.

Any advice greatly appreciated - this is also a learning exercise on these older boards so I want to do this myself.

Missing pads near IDE (LF1 & Modulator removed for easier access):


Cleanly removed audio caps (KB & Audio connectors removed for access):


Missing pad @ C304 (prior to cleanup of area)

[solarmon]

I had to do some similar repairs recently on a rev 1.5 A600 , and drew up these diagrams to help identify/map where everything was:





I hope that might help you too.

[lilwshu]

Originally Posted by BennehBoy

I wonder if anyone has a good solution for C304, the pad for this via's to the other side of the board but I can't see where the trace ends up due to the silk screening (it's in the region of R347 & R346).

If you scrape away the solder mask from the tiny bit of trace left next to the via it's probably good to solder a wire to, if not scrape it off the via itself and solder to that?

[BennehBoy]

Originally Posted by solarmon

I had to do some similar repairs recently on a rev 1.5 A600 , and drew up these diagrams to help identify/map where everything was:

I hope that might help you too.

That's fantastic, thankyou - if I'm reading it correctly it looks like I need to route that cap leg to the R347 side of C302 on the back of the board.

EDIT - revisiting this, I read it wrong, it's the other side of the cap I need to route to, ie the non ground side.

[amiman99]

My A600 had leaking caps too, when removing them I had few lifted/broken pads. I used thin repair wire to get them fixed.
You can use online schematic from https://www.amigapcb.org/ to help you get alternative signal source for your pads.

[BennehBoy]

Originally Posted by lilwshu

If you scrape away the solder mask from the tiny bit of trace left next to the via it's probably good to solder a wire to, if not scrape it off the via itself and solder to that?

The trace by the via is completely gone - I didn't want to try using the via as it's under the capacitor so I might accidentally bridge it when soldering the good pad - but I'll bear it in mind as getting a wire round the edge of the board where it touches up against the shield might also be 'fun'.

[BennehBoy]

Originally Posted by amiman99

My A600 had leaking caps too, when removing them I had few lifted/broken pads. I used thin repair wire to get them fixed.
You can use online schematic from https://www.amigapcb.org/ to help you get alternative signal source for your pads.

Thanks, I've got some 0.1mm kynar I'm going to use.

[amiman99]

Originally Posted by BennehBoy

Thanks, I've got some 0.1mm kynar I'm going to use.

Good luck fixing it. I used that website to fix my A4000, very usefull.

[andy2004]

sorry for the trouble the A600 is causing you bennehboy starting to think it would have been better to chuck it

[BennehBoy]

Originally Posted by andy2004

sorry for the trouble the A600 is causing you bennehboy starting to think it would have been better to chuck it

It's no trouble at all, I'm really enjoying it

It's no fault of yours, these caps just don't age well.

Anyway, first part of the repair is complet:



Scratching my head about the best way to get the final repair bodge wire to the other side of the board now.

PS, regarding the 2 caps with floating legs, they're getting some hot glue on them as soon as I've fitted the TH components and cleaned up the flux.

[lilwshu]

Another approach would be to scrape the via and use a through hole with tactically bent legs (this has saved me a few times in the past).

[BennehBoy]

Good idea, but I'd probably need to drill the via and I don't have a small enough bit to hand.

I've opted for a larger insulated single core bodge wire:



I'll cut a slot to accommodate it in the shielding.

[BennehBoy]

And she's alive.

Now I need to see if I can convince @solarmon to sell me an A600 PLCC RGB2HDMI adaptor

Excuse the reflected beer belly

[solarmon]

Nice one!

For the small filled/blocked vias, I got myself a hand held micro drill bit set. Also useful for those pesky holes on the ground plane!

[BennehBoy]

Originally Posted by solarmon

Nice one!

For the small filled/blocked vias, I got myself a hand held micro drill bit set. Also useful for those pesky holes on the ground plane!

I'm going to pick some up, I do have some somewhere but simply got no clue where I've put them.

[BennehBoy]

Well this is rather frustrating, I reassembled the machine after having left it to soak for quite some time. Power back on, and black screen.

I've disassembled back down to the bare board and still black screen, all my connections still look good (will tone them out next), and there's no leakage from any of the new caps.

[solarmon]

Have you checked the reset signals? You might still have problems with the reset circuitry/components - around the 555 timer (U14).

[BennehBoy]

Yeah that's what I'm thinking, I just pulled C612 as the cap base had a wobble, but it measures fine on my ESR meter.

I just toned everything out around the 555 and it seems correct, I've not traced connectivity to elsewhere on the board yet though.

The 555 looks pretty grotty tbh.

[BennehBoy]

Not sure if it's just coincidental, but I gave all the contacts a very good clean with IPA around U14, U36, and the reset circuitry transistors and discretes.

Powered back up and it starts up.

There' s a lot of grot visible under both IC's so I think I'll lift them off, clean and reflow - just need to grab some chipquick as I don't have hot air.

[solarmon]

Check ceramic cap C611 too - that can also go bad because of cap leakage from C612.