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scuzz
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A1200 capacitor lugs Posted on 19-Nov-2020 11:12:11
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Regular Member |
Joined: 30-May-2004 Posts: 365
From: New Forest United Kingdom | | |
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| 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
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Re: A1200 capacitor lugs Posted on 19-Nov-2020 16:04:14
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Elite Member |
Joined: 6-May-2007 Posts: 11181
From: Greensborough, Australia | | |
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sundown
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Re: A1200 capacitor lugs Posted on 19-Nov-2020 21:00:08
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Elite Member |
Joined: 30-Aug-2003 Posts: 5120
From: Right here... | | |
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| @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
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Re: A1200 capacitor lugs Posted on 20-Nov-2020 11:54:24
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Regular Member |
Joined: 20-Jan-2004 Posts: 397
From: UK | | |
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| @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
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Re: A1200 capacitor lugs Posted on 21-Nov-2020 15:08:17
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Regular Member |
Joined: 20-Jun-2003 Posts: 386
From: Italy | | |
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| According to amigapcb.org (and many other sites on the Web) the missing capacitor should be a 470µF 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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