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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 17th Oct 2021, 9:16 pm   #1
Retrotechie
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Default Amiga A1200 recapping

Hi, I am in the process of recapping an early A1200 main board.

I also have another A1200 with a much later (revision F) motherboard, with different branded capacitors, and the surface mount electrolytics check out more or less ok and donít show any signs off leakage (though I havenít removed any to check underneath).
Given the age, I might just recap it anyway (and since I already have it apart), but would be interested to hear anyoneís thoughts.

Also, does anyone have experience of the external PSUís ? I have two, one of which is a heavy linear type, and the other a lighter switch mode. I seem to remember having one of the linear psus fail years ago (shorted windings).

Retrotechie
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Old 17th Oct 2021, 10:45 pm   #2
SiriusHardware
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Default Re: Amiga A1200 recapping

Regarding recapping, I think many people here are in the 'if it isn't broken, don't fix it' camp.

There are certain (mainly non computer) situations where capacitors in particular circuit positions have been shown by experience to be at high risk of failure and sometimes, given their position in the circuit, may cause considerable damage when they do fail - those are the only circumstances in which I would operate a 'replace on sight' policy.

I have two Atari STs, one a 'plain' ST and one an STe - both are running on all of their original caps and I have no plans to re-cap either the PSUs or the mainboards at present. They both work, so I'm leaving them well alone.
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Old 18th Oct 2021, 8:08 am   #3
cmjones01
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Default Re: Amiga A1200 recapping

I'm not a fan of recapping in general, preferring to trace and repair actual faults. However, in a piece of equipment which makes extensive use of surface-mounted electrolytics, I'd change that view. They are absolutely awful components and not only do they fail themselves but they routinely leak corrosive stuff that destroys the PCB around them. I have an Apple Macintosh SE/30 here which needed every single one of the surface mount electrolytics replacing. They really were all faulty, in such a way as to stop the machine working and damage to the PCB was already starting.

When replacing them I used either ceramic capacitors where the circuit function allowed it, or wire-ended electrolytics tidily fitted to the original pads where the function or component value didn't permit a ceramic.

That era of electronics, from the late 1980s to the mid 2000s, used a lot of these things and they're all going to fail. They exist only to keep costs down, as far as I can see. Even today when designing electronics professionally I refuse to specify surface-mounted can-type electrolytics, and try to use a different capacitor type or through-hole electrolytic.

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Old 18th Oct 2021, 9:53 am   #4
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Default Re: Amiga A1200 recapping

Quote:
Originally Posted by Retrotechie View Post
Hi, I am in the process of recapping an early A1200 main board.

I also have another A1200 with a much later (revision F) motherboard, with different branded capacitors, and the surface mount electrolytics check out more or less ok and donít show any signs off leakage (though I havenít removed any to check underneath).
Given the age, I might just recap it anyway (and since I already have it apart), but would be interested to hear anyoneís thoughts.

Also, does anyone have experience of the external PSUís ? I have two, one of which is a heavy linear type, and the other a lighter switch mode. I seem to remember having one of the linear psus fail years ago (shorted windings).

Retrotechie
Iíve not long dragged my A1200 out and had a play. The caps looked fine and the machine is stable so not bothered recapping it. Stuck a CF to IDE adapter in and got the 8Mb memory upgrade from Amigakit, runs WHDLoad images very nicely now.

Regarding the PSUís, both the linear and switchmode types seem to use very cheap capacitors so did recap the PSUís. If you take a look at Noelís Retro Lab on YouTube he recently retrofitted a Meanwell SMPS into an Amiga PSU case, looks like this is a popular (and sensible!)conversion.

Kev
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Old 18th Oct 2021, 6:52 pm   #5
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Default Re: Amiga A1200 recapping

Funnily enough, I was watching that video from Noel the other day. I might just do that mod on one of the psus I have.

Regarding the surface mount caps, my experience of these is that they either leak, or go bad (high ESR). Iíve changed a fair few on various kit over the years. Recently, I had a Panasonic pro VHS which used a ton of these caps (some on or under hybrid ics making it impossible to fix).

As the Amiga A1200 only has a handful, itís not so bad to change them, but the print is especially fragile, and where the caps have leaked and the electrolyte has reacted with the solder, even more tricky.
I think I will recap the revision F board as a matter of course, and given these caps reputation.

Digressing slightly, i recapped a couple of spectrums (48k) last year. No surface mount here but several axial electrolytics which I replaced purely from an age perspective.
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Old 30th Oct 2021, 6:18 pm   #6
BertramWooster
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Default Re: Amiga A1200 recapping

Isn't the point with the A1200 that the capacitors are particularly poor quality and prone to leaking, thereby damaging the motherboard?
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Old 31st Oct 2021, 7:52 pm   #7
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Default Re: Amiga A1200 recapping

My experience of surface mount electrolytic capacitors is that they all go bad (either leaking or going high ESR) eventually. Certainly with this early revision A1200, there was leakage. On the later revision, the capacitors appear slightly different (different brand?) and no signs of leakage. The ESR also checks ok, although to be fair, I havenít actually removed to check properly, which is my next step when I have a bit more time, and will report back.
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