Amiga 1000 Power Supply repair?

[yorgle]

Hey all.  My Amiga 1000's power supply (dated October 1985) has just failed.  It was working last night, but this evening, I went to turn it on to listen to some mods, and i was left sad instead.

It's a late 85/early 86 NTSC Amiga 1000

Here are the symptoms:
- Power cord is functional
- Dust blown out/off the board (fairly clean for a 28 year old machine)
- switch on the side only turns on the fan (110v fan)
- Continuity test on the fuse shows that the fuse is fine
- Voltage tests on the pinouts of the output cable show 0v
- No obvious burnout marks on the board, resistors, capacitors

I'd like to repair it if I can, rather than just replacing it with a switcher.

are there common fail points in these?
is there anything I should look for?
Is there a repair manual anywhere on line (with test point voltages listed, etc)

Any help at all would be awesome

[yorgle]

JimS: I've tried it in and out of the chassis.  There's nothing coming out of any of the voltage outputs.  I'll be doing more extensive testing and repair work soon.

TCMSLP: Thanks for the suggestions.  The $29 original supply looks like a good solution if I can't repair this one. I feel like it's a linear supply, but yeah, the parts in it look more like a switcher. I can't find any details about it anywhere.

If i completely fail, and decide to go modern with it, I may put into the case, something like the PicoPSU (if it supplies enough power, otherwise, i'll make an A500-like box housing an ATX supply)  along with the "Big Box ATX Adapter to provide the other voltages and tick signal...

http://www.ianstedman.co.uk/Amiga/designs/Amiga_ATX_Adaptor/amiga_atx_adaptor.html

[yorgle]

Excellent! Thanks for the pointers, Castellen.

So, I just cracked it all back open, powered it on, and probed at it with my multimeter.  The bridge rectifier seemed to behave as I'd expect four diodes to behave.  Everything worked in the right directions.  I powered it on, checked voltages on it, and everything looked reasonable.  I've never worked on such a thing, so the +80 and -80 volts coming out of it (with 110v AC going in to it) seemed somewhat reasonable.  I had expected it to be +-60 volts, but whatever.  

There's a line printed on the board by the smallish transformer there, so I assumed that on one side it's AC, and the other side is DC... I checked voltage from ground to the heat sinks on the two transistors on the AC side, and was getting 80v, which was interesting...

I did notice one of the ICs on the DC side had a bit of dust on it, that I neglected to remove last night, so I did that.  powered it back on, and continued probing.  I had the black lead of my multimeter jammed into the black (ground) pin on the motherboard connector (not connected to the motherboard), and I started probing around the DC side.  I was getting 0v on most of the chips, then i tried one, and got 5v.  then i checked the cable, and I was getting all expected voltages again.  +5, +12, -12, ~3v (the TICK pin).  I plugged it into the motherboard, turned it on, and it powered up.

I reassembled the whole thing, turned on the switch and.... nothing.  No red LED anymore, nothing.  I was getting frustrated but then I just decided (for whatever reason) to leave it on for a few minutes, to see what happened.  After a minute or so, it came to life.  That was about an hour ago, and it's still on without rebooting or powering off.   I recopied the Kickstart floppy that failed a moment earlier (I think I put my magnetic screwdriver on it. oops).  As an A1000 owner, you can never have too many backups of Kickstart floppies!

I'll check those resistors in the future (I meant to do it, but then it came to life and I forgot) for the next time this happens.  I'm getting really quick with opening this thing.

So... do I trust it?  Probably not.  I'm still looking into my options, but being that I didn't really have the cash to do anything about it, it's nice that I got a bit more (admittedly, borrowed) time on it.

[yorgle]

You know.. I should have made the connection that it would be a capacitor thing.  I've been doing cap-kits on monitors for video games, I should have made the connection.  Feh to me.

Okay. I guess it's time to do an inventory of everything in there, and put together a mouser/digikey order!

[yorgle]

as a quick side note; I had to desolder one of the 12(?) electrolytic caps get its value. Out of curiosity, I snipped it open, and sure enough, the paper in it was damp only on about 25% of it.

[yorgle]

I have to get some time to triple-check this, but I believe this is correct for all of the electrolytic capacitors on a 110v NTSC Amiga 1000 Power Supply:

C11     2200uF  16V    
C12     2200uF  16V    
C13     2200uF  16V    

C15     100uF   25v    
C17     100uF   25v    
C19     100uF   25v    

C50     470uF   220V

C09     4.7uF   50v    
C10     1uF     50v    
C16     470uF   35v    
C18     330uF   35v
C49     10uF    85v    


C50 runs around $6.50, while the others go for $0.50-$1 US.  Priced out at Mouser, it runs about $13.50.  Here's the Mouser project for the above parts: http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=69b972847a

Remember to preserve polarity while installing them!

[yorgle]

Related:  The list of electrolytic capacitors needed for an NTSC Amiga 1000 (I don't have the board revision)

All are rated at 16v

C75 100uF (hidden near the side D9 ports)
C78 100uF
C79 100uF
C80 100uF

C49 22uF
C50 22uF
C63 22uF
C64 22uF
C65 22uF
C66 22uF

C92 47uF
C93 220uF
C95 470uF

Daughtercard:
100uF (two of them, no noticeable part number indications on the board)

[yorgle]

C49     10uF    85v    

Once I got this part out, I realized it was covered in dust and it really is 10uF, 35V.  (It's okay to put in an 85V part in there, but it's not the value on the original.)

[yorgle]

For what it's worth, I spent about a half hour last night, replacing all of the caps, and the power supply works 100% now.  Installed it into my 1000, and I was playing .mods deep into the night.  Huzzah.

My only note to people who decide to do this;

The one large capacitor, the 200v one, be sure to try to get one that's wide-and-short, rather than a thin-and-tall, because there is limited clearance inside the power supply case.  I got a tall one, and had to have it mounted almost horizontal to allow it to fit inside there.  oops!

Next up is replacing the caps on the mainboard and daughterboard... but there's no need to post updates about that.