AP1500 PSU Mod

[Risky]

Ok, the preliminary investigations are in this thread (http://www.wizdforums.co.uk/showthread.php?t=597&page=1&pp=10) but here's the final result:

http://www.veryrisky.co.uk/webimages/pumppsumod4.jpg

I've got the PSU to give 12.4V to 22.9V continuously variable from the pot which could (should/will) be mounted on the front panel with a shiny knob :D

Context

The PSU itself uses an IC to control the output voltage. This is adjusted by switched fixed resistors attached to the dial for 12,15,18,21,24V. The mod above cuts one track to cut out the switched resistor setup and replace it with the pot control.

The problem is to get the rigtht range on the control. The fixed resistance decreases by reducing steps to get from 12 to 24V. I've used a 1lk log pot with a 1.2k resistor in parallel to get close to the original 0-570R range.

If you could get a 500R log pot and attacked a 70R in series this would give a more linear voltage adjustment (sacrifyng a bit at the top). Mine doesn't quite reach 24V but I probably won't run over 18V anyway so I'm hapy.

More Pics
http://www.veryrisky.co.uk/webimages/pumppsumod6.jpg
http://www.veryrisky.co.uk/webimages/pumppsumod7.jpg

[Starbuck3733T]

Fan friggin tasting! awesome to hear you got this all worked out!

[mnpctech]

This is one slick and very useful mod. Keep us updated.

[Risky]

I was going to rehouse the PSU to make it fit in one of the few free spots I have in the case, but a quick check reveaeled that the heatsink is at +12V do its better off in its current case.

I've redone the control wire so it goes to a two-pin jumper so I can disconnect the control when I need to take things apart. The pot is safely installed in the front panel and I even drilled a little hold for the locking tab so it stays in position. I removed the existing LED (unnecessarily) but I have one on the front panel running off the output with a big enough resistor to keep it in spec at 24V.

I'll try and put together a complete how-to whne I can but its a pretty easy mod so if anyone wants to take the plunge do ask.

Oh and if anyone finds a 500R log-pot please tell me where!

[Darv]

Very cool and useful. Much better having it adjustable without having to reach inside your case.

[Starbuck3733T]

Mod guides are appreciated, especially if you can get it posted on a few front page news sites and really bring some traffic to the forum. If you need any assistance, let me know.

[Risky]

And from the front, alas it was the only knob I could find for the control:
http://www.veryrisky.co.uk/webimages/newfront.jpg

[Starbuck3733T]

I think you need to have a go at maplin or RS' catalog to find something more suitably handsome.

[Risky]

I know, I should have hunted farnell when I was ordering yet more parts last week. I ordered a current Transducer and some dome parts so I hoep to have a power readout soon!

And this is where I hit the PSU:

http://www.veryrisky.co.uk/webimages/trytidy001.jpg

[Darv]

And I thought the other side was messy :lol:

I agree you need some kind of stylish metal knob there instead.

[Risky]

And I thought the other side was messy :lol:

Now obsessively tidying the stuff that's out of siight - that's a bit scary. If Its out of the way back there I'm happy as long as its secure and not fouling anything.

OT, but for the record this is as tidy as I can manage - but I have rather more hardware in there than most folks!
http://www.veryrisky.co.uk/webimages/trytidy002.jpg

[Darv]

Now obsessively tidying the stuff that's out of siight - that's a bit scary. If Its out of the may back there I'm happy as long as its secure and not fouling anything.

Well tbh that side of my computer is a lot worse. You can't see any of it so it's okay but it really is just an unorganised mess of cables. I have to have the side panel on to keep it from falling out. :wacko:

[Starbuck3733T]

sometimes just getting stuff to blend in is easier than hiding it. I need to order some more techflex black sleeving so I can finally hide my ATX 20 pin line and front panel connector lines.