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/  Forum Index
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      /  A1200 capacitor lugs
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scuzz 
A1200 capacitor lugs
Posted on 19-Nov-2020 11:12:11
#1 ]
Regular Member
Joined: 30-May-2004
Posts: 353
From: New Forest United Kingdom

Hi

I posted this earlier on Amiga Org and thought it may be interesting here ...


I have this old Amiga 1200 motherboard that was busted when it arrived in a tower back in 2000. I bought the tower from a guy off Amibench and he very kindly sold me a fresh 1200 motherbaord to use with the tower, which I still have. The old board was shoved up in the loft and I never questioned why it didn't work. Anyway I had reason to pop up into the loft and tripped over the A1200 amongst all my cat baskets and old clothes bags. It was only when I studied the board close up that I discovered two neg/pos capacitor lugs humping away on the board. I'd like to say I knew what they were doing but I am afraid to ask. Given that the board would have been only 7 years old when it arrived I don't think the capacitor will have naturally decayed. Maybe it blew for what ever reason.

https://www.scuzzscink.com/amiga/scuzzblog_november20_1/car_sbd_181120_42.jpg

https://www.scuzzscink.com/amiga/scuzzblog_november20_1/car_sbd_181120_45.jpg

If anyone can shed some light on what these filthy lugs are doing I would appreciate it. The board is a Rev 2B so none of the wire mods around the board. All looks pretty clean. If anyone recalls the EZ Tower had a single blue wire to the centre of the A1200 power supply being fed off the main tower PSU.

There you go. What is going on here? I don't know why I think this but I have a very vague recollection of a wire being attached to the lugs. Dunno.

PS The A1200 has had a square slot cut out of the casing on that side of the machine. Maybe another clue.

https://www.scuzzscink.com/amiga/scuzzblog_november20/scuzzblogdnovember20_1801.htm


scuzz
http://www.scuzzscink.com/amiga/scuzzblog.htm

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Hypex 
Re: A1200 capacitor lugs
Posted on 19-Nov-2020 16:04:14
#2 ]
Elite Member
Joined: 6-May-2007
Posts: 10092
From: Greensborough, Australia

@scuzz

Sorry, but a few things stand out in your post.

Quote:
It was only when I studied the board close up that I discovered two neg/pos capacitor lugs humping away on the board.


Those cheeky buggars!

Quote:
I'd like to say I knew what they were doing but I am afraid to ask.


Even if they spoke English it would be rather rude to ask them.

Quote:
Given that the board would have been only 7 years old when it arrived I don't think the capacitor will have naturally decayed. Maybe it blew for what ever reason.


I think you know why!

Quote:
If anyone can shed some light on what these filthy lugs are doing I would appreciate it.


That's putting it politely.

In all seriousness it looks like it was put there as a poor substitute for a capacitor. And by itself looks like a short. Or, another possiblity, it blew its cap off!

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sundown 
Re: A1200 capacitor lugs
Posted on 19-Nov-2020 21:00:08
#3 ]
Elite Member
Joined: 30-Aug-2003
Posts: 5118
From: Right here...

@scuzz
That area of the bd looks like the power supply area. Caps of that type are usually voltage bypass caps, they just filter noise. Those 2 pins are all thats left of a blown cap. My guess it was put in backwards at build. A polarized cap will heat up over time if backwards & eventually short out & blow, some quietly, some not so quiet. Those 2 remaining pins could be shorting out a supply voltage thats stopping the system from working. That cap is probably 100uf/35V. A multimeter will show if the pins are shorted, another way is to cut one from the bd & see if it boots. I worked in electronics for 40 yrs fixing bds, my last job was with a medical company in production engineering, & I have see my fair share of polarized caps put in wrong.

_________________
Hate tends to make you look stupid...

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evilFrog 
Re: A1200 capacitor lugs
Posted on 20-Nov-2020 11:54:24
#4 ]
Regular Member
Joined: 20-Jan-2004
Posts: 368
From: UK

@scuzz

Time to put those lugs to work - find out the value of capacitance that should be there and then add in a temporary cap using the lugs. If the board fires up, all well and good, and you can reach for the soldering iron. Otherwise back to the drawing board.

_________________
"Knowledge is power. Power corrupts. Study hard, be evil."

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Turrican3 
Re: A1200 capacitor lugs
Posted on 21-Nov-2020 15:08:17
#5 ]
Regular Member
Joined: 20-Jun-2003
Posts: 338
From: Italy

According to amigapcb.org (and many other sites on the Web) the missing capacitor should be a 470F one, and I see various recapping lists suggesting a 25V rating.

I can see though that this A1200 is missing its kickstart ROMs so replacing the capacitor alone isn't going to be enough to boot.

Regarding the hole on the left side of the chassis, my guess is that there was some kind of IDE adapter originally installed.

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