A3000 PSU dead?

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sbadger
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Location: Farnham, Surrey

A3000 PSU dead?

Postby sbadger » Tue Nov 28, 2017 2:58 pm

Hi there,

I've an A3000 i'm restoring, battery damage negligible/none, removed anyway, cleaned up with 'Del' and boots no problem.
The machine has 4mb and an IDE controller + HDD. It's been working no problem but just today did a graceful down, swapped keyboard, flick power switch and nothing... dead.

Tried a multimeter on the unloaded psu spades, nothing...
edit: though realise these are switching so need a load.... #-o

Any ideas?, it's a metal case PSU rather than the card. The technical reference doesn't really mention psu. Another thread mentions a startup cap, but no more detail.

thanks
stew
A3020| A3000x3| BBCBx3 | Electrn | Masterx3 |RiscPC| RPix3
A600 | C64 bbin x2|C64C | Toastrack |QL | XB360&1X |GB |GBC |GBA |GBASP | DS | 3DS XL x2| MD | MS
Atari 7600 | PS1-2-3-4| PSP |Vita |SNES |GC |N64 |Wii & U |Switch |JammaCab |Sony PVMx2

philb
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Joined: Sat Aug 05, 2017 6:05 pm

Re: A3000 PSU dead?

Postby philb » Tue Nov 28, 2017 8:23 pm

You should see something at the spade terminals even with no load. In fact I think the A3000 PSU is modern enough that it should be able to maintain regulation just fine without any load at all.

I don't think there is a published circuit diagram for those PSUs. I imagine Acorn's attitude to them at the time was that they were cheap enough to be essentially disposable if they broke down. But on the other hand they are fairly simple (just a single +5V output) and it wouldn't be all that hard to either trace out the circuit or just swap parts until it starts working again.

Dried up capacitors usually show up as the PSU gradually taking longer and longer to start up until finally the day comes that you can't get it started at all. If it went from working fine to being completely dead in a single power cycle then that is much more likely to be a failed semiconductor of some sort. That's not to say that replacing all the electrolytic capacitors would be a bad idea, but I don't think it will solve your problem.

Does it make a noise at all when you switch it on? Sometimes you get a squeaking or whining sort of sound with failed PSUs and this can give you some clues as to what the matter is.

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sbadger
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Location: Farnham, Surrey

Re: A3000 PSU dead?

Postby sbadger » Wed Nov 29, 2017 9:25 am

No it's totally silent. Just checked the obvious things, the plug fuse, fine, internal psu fuse, fine, the rocker switch actually works, check.
A3020| A3000x3| BBCBx3 | Electrn | Masterx3 |RiscPC| RPix3
A600 | C64 bbin x2|C64C | Toastrack |QL | XB360&1X |GB |GBC |GBA |GBASP | DS | 3DS XL x2| MD | MS
Atari 7600 | PS1-2-3-4| PSP |Vita |SNES |GC |N64 |Wii & U |Switch |JammaCab |Sony PVMx2

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sbadger
Posts: 233
Joined: Mon Mar 25, 2013 1:12 pm
Location: Farnham, Surrey

Re: A3000 PSU dead?

Postby sbadger » Wed Nov 29, 2017 12:12 pm

I've ordered the caps as starting point, i'll report back.

For future reference it's a:-

Phihong PSM-054

and the electrolytics are

2x 100uf 200v
2x 2200uf 10v
2x 1uf 10v

all 105c
A3020| A3000x3| BBCBx3 | Electrn | Masterx3 |RiscPC| RPix3
A600 | C64 bbin x2|C64C | Toastrack |QL | XB360&1X |GB |GBC |GBA |GBASP | DS | 3DS XL x2| MD | MS
Atari 7600 | PS1-2-3-4| PSP |Vita |SNES |GC |N64 |Wii & U |Switch |JammaCab |Sony PVMx2

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sbadger
Posts: 233
Joined: Mon Mar 25, 2013 1:12 pm
Location: Farnham, Surrey

Re: A3000 PSU dead?

Postby sbadger » Fri Dec 01, 2017 2:31 pm

As you hinted at Phil, new caps but no dice! boooo

I've eyeballed the other components, but nothing obviouisy bad.

Are there any other common parts to fail? or how to check semiconductors?

thanks
A3020| A3000x3| BBCBx3 | Electrn | Masterx3 |RiscPC| RPix3
A600 | C64 bbin x2|C64C | Toastrack |QL | XB360&1X |GB |GBC |GBA |GBASP | DS | 3DS XL x2| MD | MS
Atari 7600 | PS1-2-3-4| PSP |Vita |SNES |GC |N64 |Wii & U |Switch |JammaCab |Sony PVMx2


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