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Old 15 May 2019, 13:58   #1
Turrican_3
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Audio issues on A600, possibly recap needed at best?

Hello everyone, I'm here again with issues on a different A600 than the one I've recently purchased.


By the way before deciding to open this thread I ran a couple of queries and I feel like this thread might be relevant despite being for the A1200, but obviously I need your help first.


So, issues have been going on for a year or so. At first I got random freezes, issue with joystick fire, corrupted graphics, and things like that.


Recently, I decided to swap the power supply with an PC one that I had on my expanded A1200, and it seems most of the issues are gone except for one: audio.


Problems seems to vary from a random low volume on a single channel to straight corrupted audio. This happens on many different games so I think it might be reasonable to believe it's not a software issue.


So, I went on and decided to have a look at the motherboard.
A couple of things immediately captured my attention, because I understand solder should look shiny while on some capacitors it is opaque instead, and also there's a worrying stain near a chip (see first photo) so I basically have two questions:


- first and foremost, do the photos suggest this motherboard might have issues with capacitors leaking, hence heavily advising a recap? Or maybe it's too late...?!
- I've noticed the capacitor near Denise is missing on this unit as well as it does on the other A600 I mentioned before (here I also see a bit of solder near the place where it was supposed (?) to be), so now I wonder if this capacitor was actually expected to be installed at all or not on the 1.5 motherboard


Here comes some photos:
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Old 15 May 2019, 14:06   #2
ajk
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Yes, definitely looks like there is quite a bit of leakage and corrosion going on there, especially in the power section. Proper recapping and possible pad repair should be performed.

The missing component probably isn't a capacitor as such, it's a place for a trimmer (variable capacitor) and has been left out on purpose. There is a splash of loose solder there, but you should be able to scrape it off easily enough.
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Old 15 May 2019, 14:11   #3
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Yep, classic capacitor failure, and leakage. Get them changed and the board cleaned up as soon as you can. With a bit of luck, the poor audio is simply a result of the capacitors failing, but it's possible there's additional damage from the leakage that needs to be repaired. The capacitors to the left of the IDE port aren't to do with the audio circuitry, but still need to be replaced as their failures are often symptomless until the leakage is so bad that it destroys the video circuitry or IDE port (or both). In this case, your instabilities could have been caused by a combination of the capacitors failing in both the Amiga and the PSU. Usually there's a certain amount of tolerance for capacitors failing in either the PSU or the Amiga, but with both failed, noisy supply doesn't get filtered and causes all sorts of trouble to digital circuits. Replacing the PSU has given you back a stable supply, so the Amiga doesn't depend on its dead capacitors to take up the slack any more.

As for the missing capacitor, do you mean C201? That's a tuning capacitor that's likely only needed by certain types of video encoder circuit. If it's not fitted (and your composite still works) then you don't need it.
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Old 15 May 2019, 14:34   #4
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Fantastic support as usual guys, and as usual I really appreciate it!
(and @Daedalus yes, I meant C201 but I'm glad at least that one is ok the way it is )

So I guess it's finally time to purchase a rework station... would this one or similar do the trick for the A600 recapping procedure I need?
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Old 15 May 2019, 16:28   #5
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Yeah, any basic hot air station will do fine. If you haven't got some experience using them however, get lots of practice in! You'll also need Kapton tape (and maybe aluminium foil) for protecting nearby parts - the keyboard connector and the nearby rear connectors in particular are easily damaged or destroyed by the heat of soldering so close to them. Removing the top clip from the keyboard connector will give you a little more room, but it's still very tight in there and needs to be carefully protected.

To be honest, if you only have one or two machines to do, it would make more sense to send the boards to someone who has experience doing them. While there's nothing particularly difficult about it, it's also easy to mess up and make the job a whole lot more serious (and expensive).
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Old 15 May 2019, 16:44   #6
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Thanks for the tips!

I had already included the Kapton tape (which by the way I discovered just a couple of weeks ago) in the shopping cart, and of course I'm planning to do a LOT of practice with one of my dead PC motherboards. Before doing anything on the Amiga, that is.

Never did any SMD stuff specifically, but I can solder and I'm definitely willing to learn more about electronics in general, maybe it's the right time to start doing so.
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Old 23 May 2019, 13:27   #7
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Sorry for the bump but I guess it's still somehow relevant.

I'm doing lots of desoldering with the SMD rework station (with mixed results, but that was to be expected I guess) and at the same time trying to understand as much as possible about the best practices...

So I stumbled on this video here:

[ Show youtube player ]

and I was wondering: what's the soldering (?) stuff being spread at about 2:30 on the caps pins with a syringe?

Do I actually need it too, or will a "regular" solder do the trick anyway?
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Old 23 May 2019, 13:54   #8
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Yeah that'll be solder paste. I've never used it personally but some people will swear by it.

It isn't necessary for this kind of work, but whether or not its preferred is something i'm not sure about.

Could you elaborate a little on 'mixed results'? A couple things i've learned over the last year or so are:

For component removal, more time and lower temp is much better than higher temps. To recap my amiga i set my (uncalibrated, mind) station to around 200 degrees. If it is stubborn i'd move up to 220, and then small increments of 10 degrees thereafter. The lower the temperature the better. This was plenty to melt the solder and remove the parts. You might even be okay with less than this, but as I say my station is not calibrated properly. (Plus you're dealing with air, so it'll be cooler when it hits the component anyway). It's tempting to just throw buckets of heat at something and get it off as quickly as possible, but this is how you pull traces up, damage IC's, and melt plastic headers.

Use a smallish tip - about the size of the component to be removed - and point it at the centre of the component. Do not point it at the pads/alternate between the pads. You want to heat the whole thing up for something like cap removal. If you select about 200 and point directly at the metal cap housing, then after a while it absolutely will free itself. 60/40 Solder melts at around 190 degrees. Use something like a pair of tweezers to try and nudge it out the way, but don't pry it free - it'll move very easily when hot enough.

John

EDIT: By the way, i'm sure this is obvious but without using solder paste you'll need to use your iron to put the new parts down. I used a fine needle tip and put a small amount of solder on one pad... got the part in place, tacked it down, and then soldered up the other side - returning to resolder the tacked side afterwards. You get the hang of this pretty quickly. Also leaded solder (i use 60/40) is a lot easier and more forgiving to work with than lead free. Since this is for home/hobby use and it likely had lead solder to begin with (did it? early 90s? someone will know), i'd personally stick with the lead stuff. Just don't eat it.

EDIT 2: Corrected the temperature.

Last edited by project23; 23 May 2019 at 14:01.
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Old 23 May 2019, 14:00   #9
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Quote:
Originally Posted by project23 View Post
Could you elaborate a little on 'mixed results'?
Absolutely: some of them went away relatively easily and perfectly.
With others, I'm reasonably sure I utterly destroyed one or both of the cap PCB pads! :-\

Definitely need to improve my technique, and I will surely start trying with you suggestions.

Thanks!

EDIT: needless to say, I am practising with long dead electronics, not with my precious Amigas!
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Old 23 May 2019, 14:06   #10
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Quote:
Originally Posted by Turrican_3 View Post
Absolutely: some of them went away relatively easily and perfectly.
With others, I'm reasonably sure I utterly destroyed one or both of the cap PCB pads! :-\

Definitely need to improve my technique, and I will surely start trying with you suggestions.

Thanks!
I'm sure some other more experienced people here can give you some better advice.

I find that removal of components is all about patience, really. I'm currently removing some ram from a stock A500 motherboard using hot air and a solder sucker. It's tempting to crank the temperature right up, especially when dealing with a pin connected to the ground plane, but if i'm patient and wait for the entire area to warm up a bit, its usually fine around the region of 280 max (remember this is uncalibrated), but that's only really for the stubborn ground plane pins. I don't believe you should ever really need to exceed this temperature.

It's sometimes taken me a good five minutes until the board is hot enough to easily remove the solder.

Try to take a look at the traces coming from the board, or even the schematics or amigapcb.org (i think?). If they're just smallish traces, then you can use a low temperature and it'll come off easy. If the traces are large then they're likely power rails, and they'll suck a load of heat up. Try not to increase the temperature, just try to be patient before attempting to dislodge the part. If you find you still need more heat then that's fine, but I wouldn't add more heat as a first port of call, ya know?

Hopefully someone else will chime in with better tips.

John
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Old 23 May 2019, 14:16   #11
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Oh also it goes without saying you should wear some safety glasses when doing this. At the lower temps, it's unlikely to be a problem, but sometimes these caps can go 'bang' - so make sure you play it safe!

I've never had this happen though - I think it happens mostly if you just through 350 degrees at a big cap, lol.

John
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Old 23 May 2019, 14:18   #12
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Yep, leaded all the way for Amiga stuff. Even commercially, leaded solder is still perfectly legal to use for repairing old (pre-2006) equipment, and Amigas most certainly did use leaded solder. In fact, mixing different types of solder is best avoided.

Generally good advice there, the only thing I'll add is that pre-heating the board will help a lot. some people have board pre-heaters which are amazing, but expensive (especially for the size of an Amiga motherboard). Spending a bit of time with hot air at 120-150 degrees or so to warm an area of the board will help a lot. The A600 isn't so bad because of its construction, but the A1200 really benefits from pre-heating as it has two internal layers that are essentially solid copper and serve to quickly sink heat away from the pads on the surface.

If you have an oven with a well controlled temperature setting, heating the board to 80 or 100 degrees or so will do a similar job. Just make sure you know your oven - many domestic ovens go far above what their dial says when they're set to low-ish temperatures.

I personally find solder paste is lovely to work with, but it's also easy to mess up. Too much and you risk forming catastrophic shorts under your parts, but the right amount will give you absolutely perfectly formed joints every time. I sometimes use it for capacitors, but mainly for replacing parts with more than 2 pins.

Edit: I've had a couple of particularly fishy capacitors go bang on me. The tell-tale sign that it might happen is that they started to rise up out of their plastic bed. This was a CD32 that had a lot of leakage and those capacitors were in particularly bad shape.

Also, one other tip for stubborn parts: If the solder is dull from corrosion due to leakage, it will take more heat to melt it. Flux can help here, a little dabbed on each leg will lower the temperature needed.
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Old 23 May 2019, 14:23   #13
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I'll have to give solder paste a go some time... How is it for really small pin pitches on CPLDs etc?

Also yeah, I don't know why i didn't think to pre-heat my boards first with a lower temperature. I'll give this a go today when I return to the ram on the A500. I can imagine that's much less stressful for the board than simply going straight in with 250+
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Old 23 May 2019, 14:33   #14
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Precious advice as usual guys!

Regarding oven and preheating... I think I might give it a try as well (of course, again, I won't even barely touch my Amigas unless I'm 99% confident I can do the job), I have a couple of ways to measure temperature so it should be highly unlikely for it to "overshoot" as long as all of them show the same-ish reading - and the thermostat is working, that is.
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Old 23 May 2019, 14:53   #15
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Indeed, pre-heating prevents a lot of stress from localised heating too, added bonus Especially with multi-layer boards, rapid heating in a small area can cause warping, or even worse, delamination of the board in extreme cases.

It's a good idea to stick a thermometer probe in with the board to keep an eye on it. Especially at low temperatures, an oven might have hysteresis of 30 degrees or more, which could be the difference between a preheated board and a preheated board with melted connectors.

At some point, I'd love to have the space for a reflow oven, or do a DIY reflow setup with a countertop toaster oven.

As for the paste, I've used it for soldering the 68020 on an A1200, which has a pitch of 0.65mm. I used a mylar template for that though rather than free-applying it. It was a little fiddly but worked fine. Controlling the amount of paste applied to each pad is the key. Stencils made soldering the larger pitch PLCCs a dream though!
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Old 23 May 2019, 15:04   #16
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I apologize in advance for the dumb question but... is there a difference between solder paste and soldering paste?

I have a feeling (not a native speaker unfortunately) than the answer is yes, but I'm a bit confused.
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Old 23 May 2019, 15:07   #17
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Nah, no difference - I personally think of it as 'solder paste' as it is solder, and is a paste... I guess? haha

But you do solder WITH it, so i dunno maybe solderING paste? haha

Paste of solder. That's how I would think of it.
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Old 23 May 2019, 15:13   #18
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Got it!

Sorry but having to learn many new things (never used flux before for example) AND terms often in a foreign language can lead to... err... unpredictable results.
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Old 23 May 2019, 15:45   #19
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No harm in checking But yes, pretty sure they're one and the same. Solder paste is basically just tiny beads of solder mixed with a thick flux, so you get both parts in the one product. Unlike the wire however, there's a higher flux:solder ratio in paste, which makes adding additional flux generally unnecessary.
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Old 23 May 2019, 16:24   #20
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Is there any difference in quality of solders types e.g. would lead-free solder be as good as normal solder?
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