Repairing Amiga 500 PSU

hese · 06 January 2010, 16:42

I had been using my Amiga 500 for an hour when suddenly the PSU began to fluctuate the power. The computer turned on and off multiple times in a short period of time (some seconds). I turned the PSU off and back on after a while.

The A500 seems to start normally but the caps lock led is on all the time. I can boot the computer from a floppy but after reading a couple of tracks it loses power and reboots.

I measured the voltages from the 5 pin power connector and got bizarre results:

Code:

   Expected  Measured
   +5 VDC    +6.5 VDC
   +12 VDC   +12 VDC
   -12 VDC   +23 VDC  !!!

The A500 is not broken, it works fine with another PSU.

I'm planning to repair the PSU but I don't know what's been broken. Some capacitors? Any ideas?

Anemos · 06 January 2010, 17:35

-12 VDC +23 VDC ?
no is not only capacitors .. looks like fault IC,diodes,ect..

Paul_s · 06 January 2010, 17:39

use an ATX psu. The 500 power supplies are long past their sell by dates and you'd be mental to play with something like that....

Anemos · 06 January 2010, 17:52

ι agree one stable PSU from PC is the best way.
dont trust any more this faulty A500 PSU ,even then repaired.

cosmicfrog · 06 January 2010, 18:07

yep hack the lead of old power brick and put it on pc power supply

old AT psu`s are my perferd ones as less mucking about to do + I like the big switch

but modern atx power supplies can be made to work as well

prowler · 06 January 2010, 22:04

Quote:

Originally Posted by hese

I measured the voltages from the 5 pin power connector and got bizarre results:

Code:

   Expected  Measured
   +5 VDC    +6.5 VDC
   +12 VDC   +12 VDC
   -12 VDC   +23 VDC  !!!

Hi hese,

If those voltages were measured under open-circuit conditions, i.e. without being connected to your Amiga's power input socket, then the results will be bizarre.

To get true indications, the voltages should be measured at the power input socket from inside your Amiga with the Amiga switched on.

Supamax · 06 January 2010, 22:16

Quote:

Originally Posted by cosmicfrog

modern atx power supplies can be made to work as well

How?

prowler · 06 January 2010, 22:32

Hi Supamax,

See Zetr0's Schematics Collection.

Look for the Using an ATX / BTX PSU for AMIGA A600/A1200 schematic in the opening post and there is a further diagram in post 3.

Chain · 06 January 2010, 23:25

Quote:

Originally Posted by Paul_s

use an ATX psu. The 500 power supplies are long past their sell by dates and you'd be mental to play with something like that....

so i am one

Supamax · 07 January 2010, 12:57

Quote:

Originally Posted by prowler

Zetr0's Schematics Collection.

Look for the Using an ATX / BTX PSU for AMIGA A600/A1200 schematic in the opening post and there is a further diagram in post 3.

WOW, thanks!
I didn't know that thread

hese · 12 January 2010, 09:54

Apparently there was nothing wrong with the PSU after all. The problem was caused by a faulty mouse cable, it short circuited the machine occasionally.

Quote:

Originally Posted by Paul_s

use an ATX psu.

An ATX PSU is one option. Although the metal brick on a table does not look good nor safe.

Quote:

Originally Posted by Chain

so i am one

There's nothing wrong with that. I'd do the same.

rkauer · 12 January 2010, 17:00

If you are worried about the (shielded!) metal, sack the guts of the ATX and place it inside the old A500 brick's case.

But in this case you need to source a mini or "baby" ATX PSU. Regular size ones don't fit inside the old plastic brick.

06 January 2010, 16:42	#1
hese Registered User Join Date: Sep 2008 Location: Somewhere Posts: 223	Repairing Amiga 500 PSU I had been using my Amiga 500 for an hour when suddenly the PSU began to fluctuate the power. The computer turned on and off multiple times in a short period of time (some seconds). I turned the PSU off and back on after a while. The A500 seems to start normally but the caps lock led is on all the time. I can boot the computer from a floppy but after reading a couple of tracks it loses power and reboots. I measured the voltages from the 5 pin power connector and got bizarre results: Code: Expected Measured +5 VDC +6.5 VDC +12 VDC +12 VDC -12 VDC +23 VDC !!! The A500 is not broken, it works fine with another PSU. I'm planning to repair the PSU but I don't know what's been broken. Some capacitors? Any ideas?

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06 January 2010, 17:35	#2
Anemos 70X7 Join Date: Apr 2008 Location: Ἑλλάς Posts: 1,078	-12 VDC +23 VDC ? no is not only capacitors .. looks like fault IC,diodes,ect..

06 January 2010, 17:39	#3
Paul_s Registered User Join Date: Nov 2006 Location: Amigaville Age: 46 Posts: 3,336	use an ATX psu. The 500 power supplies are long past their sell by dates and you'd be mental to play with something like that....

06 January 2010, 17:52	#4
Anemos 70X7 Join Date: Apr 2008 Location: Ἑλλάς Posts: 1,078	ι agree one stable PSU from PC is the best way. dont trust any more this faulty A500 PSU ,even then repaired.

06 January 2010, 18:07	#5
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	yep hack the lead of old power brick and put it on pc power supply old AT psu`s are my perferd ones as less mucking about to do + I like the big switch but modern atx power supplies can be made to work as well

06 January 2010, 22:32	#8
prowler Global Moderator Join Date: Aug 2008 Location: Sidcup, England Posts: 10,300	Hi Supamax, See Zetr0's Schematics Collection. Look for the Using an ATX / BTX PSU for AMIGA A600/A1200 schematic in the opening post and there is a further diagram in post 3.

12 January 2010, 17:00	#12
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	If you are worried about the (shielded!) metal, sack the guts of the ATX and place it inside the old A500 brick's case. But in this case you need to source a mini or "baby" ATX PSU. Regular size ones don't fit inside the old plastic brick.

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