I fried my A3000 PSU!

[Blatboy]

If you have built power supplies you know the chain. Test output from transformer then move to full wave bridge and down the line for each voltage output. you'll find it.

Chris

Yes!  I know the chain.  It's great to be reminded of the process though.  Thanks.  Seriously.

Yes, you will have to test for voltage (the DC rails) with the power ON, BE CAREFUL.  Nicola Tesla always kept one hand in his pocket while testing to kepp dangerous voltages away from his heart.  Many of the components, heat sinks, traces, etc will have dangerous line voltage on them!  You may have decided that going inside the PS box is not worth the risk.  No harm done.

That is probably the only thing Tesla and I have in common. Haha.  I feel more comfortable dealing with a PSU than I would sensitive CMOS components or logic components or something like that at this point... so I'm going to take a good hard look at that PSU before I go ATX.  It's always an option though, thank goodness.

When testing the supply, I would load all rails simultaneously with resistors.  Lets revisit those loading resistors.  Using Ohm's Law, a 30 ohm - 5W resistor will load the 12 V rails, both the + and the -, with 0.4 amps.  MAKE SURE all rails are rated (read the tag on the PS box) for more current than what the loading resistors will draw!   If not, adjust the resistance values UP accordingly.  The +5 VDC rail could typically take a 15 Ohm - 5W resistor.

If you are getting outside of your comfort zone, google Ohm's Law. You could also run these tests first on a known-to-be-good PS from a disposable PC and monitor how it behaves.  

PS fans are often powered by the +12 VDC rail rather than the 120 VAC line.

I'm no stranger to Ohms law.  That said, the process is everything and this is very helpful.

And re: hot snot... I guess it's just isopropyl one needs to get rid of it.  That, I have.

https://www.youtube.com/watch?v=dNNqSXgj6DE#t=96

This is great!  Thanks for the help!!!

[Blizz1220]

@Blatboy

When you said smoke did it smell like caps leaking in air spray form ?

Smell is really hard to miss as it smells awful.If Amiga was still showing
picture when smoke came out then caps are your culprit.

Even if they are just a little rised on top you should replace them first ,
some atx PSU won't turn on with blown cap and you should really check
the bottom cause they get bad there as well as the top.

As for the rest components (from experience of fixing mostly ATX PSUs)
the component that fried is black and looks fried , i used that test mostly

No experience with A3000 PSUs though.If you get it running (or convert
to ATX) you can check the voltages by setting multimer to 20 V and check
every line (using PSU chasis as ground).Make sure it's quality ATX PSU as it needs -12 V more than regular PC does.

White translucent stuff is just there to keep components in
place and can be safely peeled away

On the side note , close PSU before testing voltages on pins ,
I didn't bother to do that until it blew spark in my gazing eyes.
If it blows up closed it's less of a problem.

[Blatboy]

Oooh.  Thanks!  That gives me hope.  Replacing caps I can do.  (famous last words)  And I'll remember to put the cover on when testing...

[Blatboy]

Resistors and Caps ordered.

I'll tell ye how it goes...

[Castellen]

I'm a bit lazy and only skim read this thread, but unfortunately this doesn't sound like a typical capacitor problem, especially if you've seen no visual signs of leaking or deformation.

I've noted many of the common problems I've found with A3000 power supplies over the years here:
http://amiga.serveftp.net/A3000_HardwareGuide/booting-problems.html

Look under the 'A3000 power supply common faults' section.

The standard repair process for any such switchmode supply: Check you have about 320V (150V for US models) across the main reservior capacitor - which is the big one.  If not, it's a fuse or bridge rectifier fault.  And usually these fail due to something else going wrong further into the supply.  If yes, it's often a problem with the high voltage chopper transistors (though these usually fail short circuit which blows the fuse and sometimes damages the bridge rectifier in the process) or the low value series resistors (these always fail open circuit).

If that all checks out OK, you might have a switchmode controller fault which is more complicated to diagnose and repair, but this kind of fault is usually less likely.

Hope that helps, good luck with your repair job.  And it certainly doesn't hurt to replace aging capacitors, so keep them on order.

[Blizz1220]

"I do have the know how to replace the caps in the PSU,
which look a little bloated."

I would say they need changing either way :hammer:

What I was wondering is was Amiga displaying picture (still
working) when smell came out.I don't know what else could
go bad with picture still on except caps.

Although bad cap will make transistor overheat but as far as
I know if it dies in the process no picture.

[Blatboy]

Yeah, the screen was fine when I smelled smoke.  The fuse is ok. I think it was a short though the chassis to the motherboard that may have caused the fault. (I did a half assed job of reassembling the computer to test.)   Hopefully nothing else got fried.  Thanks for that extra info about the main reservoir caps!

[AmmoJammo]

did you plug the floppy drive power connector offset to one side?

[Blatboy]

The floppy's power was connected... though I believe there was another molex there that wasn't... and, yeah...who knows where that thing was.

[Blatboy]

Well, I was finally able to open up my PSU last weekend and test it.  Everything more or less seemed ok, believe it or not.  Boy those load resistors got hot.  I expected that though.  

Regardless, since I had already purchased the caps, I replaced the caps on the PSU with some high quality new electrolytics.  

I reassembled the PSU and installed it in the A3000.  It worked... to an extent.  However, I do feel 90% sure the power supply is ok.  I'm going to do one more little bit of testing with it to turn that 90% sure to 100% sure before I move further.

I do have some other issues (story of my life) but I'll spare you those until I've confirmed that PSU can't be an issue, and only then will I start another thread of questions.

I wanted to make a special point to thank for all your helpful suggestions (especially you Tenacious for your detailed explanation of using load resistors.)  I really appreciate it!! You all are a huge help.

[Tenacious]

It's very good to see people tackling the problems of vintage computers without giving up.  I think many are interested in how you solve the problems at hand.

Just to mention it, Ive had my A3000 appear completely unresponsive in the past (especially after being opened and disturbed) and it turned out to be dirty oxidized connectors where the MB mates to the Zorro daughter board.  Food for thought.

[Blatboy]

Interesting you say that.  Is that just a matter of cleaning the contacts w/isopropyl?

Here's the update:

I did a double check of all the voltages coming from the PSU and every output seems to check out ok.

However, I only get the screen asking to enter a floppy. (Which is further than I got after I thought I fried it, and before I replaced the caps.)

The power light and the drive lights don't come on.  The light on the hard drive comes on, but it's obviously not booting from it.  This is still consistent w/what I've read (thanks Castellen!) as symptoms of a power supply issue.  However, the power supply fan does work...

When I originally got the computer, this was also a problem.  However, when I hooked up a bunch of SCSI equipment to it (that came w/the computer) the computer magically booted from the HD, and the power/drive leds worked.  Now, when I hook up that SCSI equipment, in ANY configuration, it still won't boot up from the HD.  Furthermore, one piece of equipment, an Iomega Bernoulli, now, when it's connected and powered up, the A3000 power supply won't even turn on.  (something shorted?)  Ugh.  I worked with SCSI a lot in the early 2000s on Macs.  I remember feeling like SCSI was some voodoo technology hahah.  

That said, this makes me think that there still may be an issue with the power supply.  If the output voltages read ok, and I have new caps, does that rule out a problem with the power transistors or the rectifier?  Or could that still be an issue?

What I have done:

• Replaced the caps in the PSU with quality Nichicon caps
• Double checked output voltages on all pins - all good here
• Checked pin 24 on the external SCSI port for a reversed diode - I get 5V when power is on - no continuity to ground when power is off - seems ok
• Checked the jumpers on the HD - it is terminated
• Made sure all ICs are seated well (as well as the 3640)
• Tried powering up with no Zorro cards attached
• Tried powering up with just one card attached (I only have two)
• Tried powering up with no floppy attached
• Tried powering up with every possible combination and order of SCSI devices to see if I could recreate the earlier configuration that booted.

There is no problem with the battery.  It seems the previous owner took care of that (replaced it) before it became an issue.

It has a 3.1 ROM.  I think it's running WB 3.1 on the HD as well, if I remember correctly.  From the looks of it, it's pretty maxed out on RAM.  It's a tricked out A3000.  I want it to work!  :) :)

[Blizz1220]

@Blatboy

Next step I would do is start workbench Install floppy and
try to see if HD is there and recognized and if not try to
initialize it and set up partitions.

Also check if HD survived voltage shocks sigh.

[Blatboy]

That's a good idea.  I've yet to get the floppy to boot from a disk, but I'm using 20 year old WB disks.  I'll make a new on on my 1200 and give that a go.  Not 100% sure the floppy drive is good.  I don't remember it reading anything correctly in the short window I had the computer working.  That said, I had 2 other floppy drives hooked up at the time and I didn't make good notes of what worked and what didn't.

Thanks

[Blatboy]

One problem leads to more...

Seems the floppy drive doesn't want to play nice.  I created new 3.1 Install and WB disks using my 1200.  DF0: on the A3000 keeps saying "Not a DOS disk in device DF0".  I took an old floppy drive from an A500 that I know isn't working (gee I wonder where this is going) and it almost worked...at least it got to the WB screen... but then I got errors.

I guess if I'm going to go this route to see if the HD shows up with the 3.1 install disk, I'll need to pilfer a working floppy drive from my 500 or 1200...

My gut still thinks it's a PSU issue, especially since the power and drive lights aren't lighting up on the front panel.  When the computer worked magically before, those lights came on. I think perhaps the HD isn't getting enough juice or something. I'll take the PSU apart again and test the rectifier, which I neglected to do before.  That said, if the rectifier or the power transistors were failing, I wouldn't be getting correct voltages on the outputs, right?  

I don't really have a way to test the drive, as I don't have another machine that takes SCSI drives (ok I have a Mac Classic II but I don't think that will do me any good at all.)

[QuikSanz]

It is possible to get correct voltages and still fall down under load but not typical. Disconnect the HD and see if it will boot from floppy.

Chris