PSU -help needed URGENT-

[orange]

Can I turn on PSU without A500 connected? Its "light" type, (switch?) and I know it shouldn't be ON without any load, but its needed just for a quick check if it works.

If yes, what voltages should be expected (normal, higher or lower)?

[blobrana]

Hum,
This is looking directly at the connector coming FROM the power supply:



Taken from the bottom of an Amiga 1200 PSU.



PIN Description
1 +5V
2 Shield Ground
3 +12V
4 Signal Ground
5 -12V

Yeah, should be ok to turn on power

+5 Should be, say, -/+ 0.12 volts
+12 Should be, say, -/+ 0.2 volts...

[bloodline]

Didn't the low end Amigas have a PSU tick?

[orange]

Great, thank you blobrana.

 :-)


This is what I got:
+5,17V
+11,49V
-9,8V
(A500 disconnected)

Previous owner told me A500 was dead and it showed black screen instead of hand_holding_diskette
Could the PSU be the problem?


@bloodline A2000 has TICK, so maybe its quite the opposite?

[BoingBoss]

Hi orange,

From what you have told us, your power supply is bad.  The -12 volts is too low.  Get yourself an PC AT power supply out of an old PC.  Then cut the cable with the square connector off of the Amiga 500 power supply and strip the wires and solder to the power cable coming from the PC AT power supply.  Use the connector with the orange wire.  That is the power good wire.  It needs to be soldered to one of the black wires.  The following wires from the PC AT power supply is what you will be soldering to the Amiga 500 power connector.  Red = 5 volts, yellow = 12 volts, blue = -12 volts, orange = power good, and two black wires which are ground.  These 6 wires are together on one connector.  Cut that connector off and strip the wires.  After you are done you will have a fan-cooled "Big Foot" power supply that will work with the Amiga 500, 600, and 1200.   :-D

[Doobrey]

Doesn`t look too bad, like BoingBoss said, the -12V looks a little low.. but you`re testing the voltage without load so it`s only a ballpark figure..plus your voltmeter could be out of calibration..
 But it shouldn`t stop the A500 booting as it`s only used for sound and serial port.

Are there any noises from the floppy when you power it up?
Does the power LED come on, or flash?

Have you done the tried and tested method of reseating all socketed chips on the motherboard?

[orange]

OK, I've connected amiga 500 to it and it works just fine. Haven't tested sound and serial yet, though.

512K RAM expansion wasn't put correctly (half of it was not connected), that was probably the cause. BTW, its extremely small, I'll scan it. (wish the battery wasn't so big to get sharper scan, oh well..:roll:).
It has GP battery (NiCd) that didn't leak (once again). Seems that GP doesn't leak, only Varta. I'm in doubt about replacing it with lithium, because there is little space for it.

[blobrana]

Cool,
the hardware is surprisingly resilient...

- though it may  not  survive an atomic EM-pulse.

BTW , i wouldn`t bother with the -12volt discrepancy, it`s not that critical...the other values are ok, given it`s age and your hardware power demands...

But as BoingBoss implied sometime in the future when you upgrade your setup, you can always hook up a cheap PC power box...

[Wibbly]

I had my A1200 hooked up to an ancient PC PSU, which I unsoldered the connections from my Atari ST in order to use it on the 1200  :-D
(by ancient, I mean it came from a junked PC my uncle had in order to replace my dead ST PSU, and that was back in '88 or summat)

WHen my 1200 PSU died, they wanted 120 quid for a new one. Having seen inside it, I can't believe it was ever worth that, even a hundred years ago...

[bloodline]

So where does the A1200 get it's Power Tick from?

[JimS]

bloodline wrote:
So where does the A1200 get it's Power Tick from?

The schematics say it comes from the horizontal sync... which is odd, since in the 2000, if you change the jumper to run without the tick, it uses vertical sync. If memory serves, you can't get a toaster or some genlocks to work without the power supply tick.

[Schoenfeld]

Don't worry about the negative voltage being off that far. The sound might be a little distorted, and your serial connections might be limited in speed with that voltage, but the rest of the computer will work just fine.

The A500 and A1200 computers work fine even completely without the negative voltage.

Jens Schoenfeld