Power leads going into A1200?

[blakespot]

I just posted a followup to a post I made some time ago asking about A1200 power, but it's a distinct sub-issue and I'd really like some feedback, so I am making a distinct thread.

I have an A1200 that is towered in a case w/ a PSU and power adapter cable from Revanche LLC. I got it 9 years ago. The PSU has died.

I wanted to replace the PSU but no current PSU out there has the odd-ball aux power connector that the Amiga adapter cable (just a cable, no hardware on it) plugs into, anymore. That connector is here:

http://www.playtool.com/pages/psuconnectors/connectors.html#aux

So, I ended up ordering one of these:

http://www.ianstedman.co.uk/downloads/AmigaATXpoweradaptorinstall.pdf

To slice and wire my existing Amiga to PC power cable into, plugging the main ATX lead into this board. (That document shows the standard A1200 power wiring arrangement.) Got everything in hand. So, I set about testing the lines on the adapter cable (pictured in attachments) with a digital multimeter. What I found is surprising.

There are 5 pins on the Amiga 1200 adapter plug. The plug that came with this A1200 tower has 4 wires coming off of it.

Only TWO wires are showing continuity from the freshly stripped end to the pin on the A1200 power plug. Just +12v and -12v. No ground, no +5v. Could this be the intended config, or should I conclude that the two other wires coming off the plug have recently become disconnected from the pins inside the rubber housing?

I had been using the Amiga 1200 with that config, plugged into my old ATX PSU with floppy power going into the Amiga 1200 floppy power jack for quite a while, before that PSU died.

Is it dangerous to wire it this way - just +12 and -12 going into the Amiga? I could try to tie one of the other cables into ground and another in +5 but the little cable has a melted-on rubber cover that prevents me from getting at the pin connections without tearing the thing apart.

Thoughts? Thanks.

[AmmoJammo]

sounds broken.

if the plug that goes into the 1200 only has the + and - 12volt lines still connected, it would mean that the motherboard would be getting its ground from the floppy connector, via the ribbon cable, and wont be getting the +5volts at all...

I wouldn't even be using it.

are you sure the old PSU was even faulty?

[AmmoJammo]

I wanted to replace the PSU but no current PSU out there has the  odd-ball aux power connector that the Amiga adapter cable (just a cable,  no hardware on it) plugs into, anymore. That connector is here:

http://www.playtool.com/pages/psuconnectors/connectors.html#aux

and that isn't the connector your power supply used, this was already discussed in the other thread.

If it used that connector, you'd be giving the A1200 3.3, and 5volts.

As I already said in the other thread, your old power supply had an AT power connector:

http://www.playtool.com/pages/psuconnectors/connectors.html#oldpc

with +5volts and +-12volts.

edit: heres the other thread for those wanting the background info:
http://www.amiga.org/forums/showthread.php?t=62317

[blakespot]

I had overlooked that reply, it seems, AmmoJammo.

And, indeed, in the interest of brevity I left out a step. The orig PSU died, and I replaced it with a PSU lacking the connector I needed, and so I hacked up the main ATX lead and wired into the Amiga power interface converter cable. Things worked for a while, but then got odd and stopped working altogether.

I do hope I did not wire something incorrectly and cause harm.

What I found re: the A1200 interface cable is accurate tho - just +12v and -12v. I've started slicing into the rubber to get at the pin's around back, but it's a mess. It's like tar.

So - what is the cheapest route for me to get a cable that will physically plug into the A1200's rear power connector? I have a standard ATX PSU and an adapter board to feed out proper voltage lines from that. I just need a cable / connector that I can splice into the board.

Functional PSU bricks on eBay seem not so cheap. Other ideas?

Thanks.



bp

[AmmoJammo]

Solder wires directly to the bottom of the A1200 board.

Leave the original connector intact on the motherboard.

You could even use a standard 4 pin hard drive connector for the +12 and +5volts, and just a spade terminal for the -12volts.

[blakespot]

Eh. Any other options?



bp

[blakespot]

Solder wires directly to the bottom of the A1200 board.

Looking at the bottom of the board and then the connector on the top, I am not 100% certain where each pin is coming out on the board, from the connector. Is there a map of the board contacts corresponding to signal or position on the connector someone can point to?

I guess I may as well solder to the board.

Also, what gauge wire should I use, given that this is a power lead. I don't want to go too small and melt the shielding, etc. Thanks.



bp

[blakespot]

I soldered onto the bottom of the board directly. It's not the cleanest job ever carried out, but there are definitely no terminals accidentally fused together.

I connect the ATX and it won't turn on - no fan on PSU. I remove the Amiga's lines from the ATX adapter board I purchased, and the fan and HDs fire up...

So I went to checking continuity between the visible back part of the power jack and the solder points below the board and ultimately noticed that when I test the +5v line and the -12v line -- testing them with my multimeter -- there is no resistance between those two bottom board points -- it's exactly as if I crossed the two sensors on the multimeter directly.

Is that a normal thing? Trying to diagnose, here.

Thanks.



bp

[AmmoJammo]

I'm beginning to think you should have gotten someone else to do it for you.

If you measure between the 5 and -12 with the leads around the other way, does it still show a short circuit?

[blakespot]

I'm beginning to think you should have gotten someone else to do it for you.

If you measure between the 5 and -12 with the leads around the other way, does it still show a short circuit?

I spent a great deal of time studying the backend of the jack on top and then where it goes into the board below. I feel rather certain that I made the right decisions in soldering on the lines. And I am certain none of the solder joints bridge across to other contacts.

I am quite sure nothing I have done could have caused a short between -12 and +5. It just seemed odd to see that result.

And, yes, regardless of polarity on the sensors, I see a full short with same reading as when I touch sensors directly: (0.00)




bp

[AmmoJammo]

could you please take a clear photo of the bottom of the board?

[blakespot]

Here is a shot. I used heavy gauge wire that was part of the ATX PSU that I spliced up, earlier. Was a bit harder to work with than wire I've more experience working with.

As I see it, the colors are:

yellow: +12v
blue: -12v
red: +5v
orange: GND

Thanks for looking.




bp

[AmmoJammo]

your +5 volts is connected to the ground plane.

I'd suggest using a multimeter to figure out where each pin goes, and rather than solder to the underside of the connector, solder to the row of 4 pins just down from the connector, as they're a larger pad to try and solder to.

[AmmoJammo]

your +12volts also appears to be connected to ground.

[AmmoJammo]

I went and checked my spare, dead A500 motherboard.

-12volts is actually in the right place! that's a start... :/

and your ground is connected where +12volts should go...

It appears you've swapped every connection from left to right.

I have no idea if the motherboard will still work after this abuse.