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#136721 - 05/01/03 01:12 PM Amiga computer power supply  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,393
Vienna, Austria
Yesterday I bought an old Amiga 2000 PC. The power supply is shot. When I first powered it up not even the fan turned. At the third try the fan suddenly turned, intermittently. Each time I hooked up a load (tried a 1.2 GB HD) smoke rose. There is a hard yellow mess on several components, all over the board, it's impossible to tell where it came from (not near any openings). After we removed some of the stuff (mostly from a cooler) I got about 3 to 9 V fluctuating on the 12V line and no smoke. Several tries later I was at 7 to 9V. The fan got faster, then slower again in cycles of a few seconds (maybe 10), along with the voltage jumps. Hooking up an older 130MB HD got me a faster fan and consistent 9.15 V on the 12V line, but the disk doesn't spin up.
Have you got any idea? I'm not really into electronics, and I'm aware of the fact that there are quite strong capacitors inside such a power supply, but if there's any chance I'd like to fix it.

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#136722 - 05/01/03 06:04 PM Re: Amiga computer power supply  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Easy enough.

Crack it open and replace electrolytic capacitors (those round cylinder things) -- those things always fail. NOTE: REMEMBER TO OBSERVE POLARITY or you will destroy your new capacitors.

Next, check resistors and replace any that are out of tolerance (you can check these in-circuit with an ohm-meter). I assume a diode or two may have also given up the can check those with an ohm-meter also.

You shouldn't NEVER plug in old electronics it in like that....especially if it's been out of service for so long!!!

I don't know if there's a transformer in these things, but if there is, you should have plugged the power supply in series with a 60 watt lightbulb in order to limit the current.

If the bulb glows brightly, then your transformer probably has a short-circuit in the primary.

That yellow crud may be wax from the way of knowing until you open the case.

If you plan on doing any soldering, use a 30-watt soldering iron and ROSIN CORE solder (not acid core) available at any hardware or electronics store - also use a heat-sink (a pair of locking hemostats are good for this) . This should be enough for most electronics.

Anything higher and you could scorch your circuit board and the components.

P.S.: What do you do with such an old machine? Do you collect them?

Good luck!! [Linked Image]

#136723 - 05/01/03 08:31 PM Re: Amiga computer power supply  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,211
SI,New Zealand
That yellow stuff is Adhesive, it keeps the components solidly mounted, especially where vibration is present.
I have heard that this stuff can become conductive after a few years and cause all sorts of problems.

Let's face it, these days if you're not young, you're old - Red Green grin

#136724 - 05/02/03 05:34 AM Re: Amiga computer power supply  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Tha adhesive used on some of the units is a real pain when it comes to replacing components, especially the radial-lead electrolytics which have their leads cropped very short.

It sounds as though that supply may have overheated at some point in the past.

#136725 - 05/02/03 09:08 AM Re: Amiga computer power supply  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,393
Vienna, Austria
It hasn't been out of use for such a long time, 1 year max. It gave up the ghost and the owner didn't want to start looking for a new power supply, so he gave the entire thing to Ebay.
When I opened the case i found that yellow crud everywhere. it's mostly seeping out beneath some of the big capacitors, but some of it also got elsewhere, for example on 2 big copper coils (it even connected them) and on some kind of cooler. On this cooler it burnt and smoked. After we removed some of the most obvious "connections" we got the inconsistent voltage. There'S none of it near the transformer or near the ventilation openings. It seems there's no dead short, the internal primary fuse doesn't blow. I'd have put in a PC power supply, but the Amiga needs a special 50/60 Hz(?) Tick signal.
Yes I collect old computers. I got old Macs, 2 Ataris, a C64, C128, Amiga 500 and PCs from XT up.
Did you know that Amigas are sold again? Amiga G3/800 MHz mainboard is 800 Euro.

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