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Old 22 March 2012, 01:08   #21
prowler
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I'm sure that the PSU cannot be tested without connecting a load to it. Any voltage readings you get directly from the output pins of the PSU will be unrepresentative or non-existent until the PSU is connected to the Amiga, because this will complete the circuit and allow the power rails to stabilize.

The way to test the PSU is to remove the top of the Amiga's case by removing the screws from underneath and then lifting the top away from the base at the front and then pushing it backwards slightly to disengage it from the catches at the back.

There should be sufficient clearance around the power input socket to apply the testmeter probes to the power connections even without removing the RF shield (if fitted).
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Old 22 March 2012, 09:27   #22
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Thanks for that prowler, i had forgotten it must be under load. I did indeed test it on load.
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Old 22 March 2012, 09:27   #23
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Quote:
Originally Posted by prowler View Post
I'm sure that the PSU cannot be tested without connecting a load to it. Any voltage readings you get directly from the output pins of the PSU will be unrepresentative or non-existent until the PSU is connected to the Amiga, because this will complete the circuit and allow the power rails to stabilize.

The way to test the PSU is to remove the top of the Amiga's case by removing the screws from underneath and then lifting the top away from the base at the front and then pushing it backwards slightly to disengage it from the catches at the back.

There should be sufficient clearance around the power input socket to apply the testmeter probes to the power connections even without removing the RF shield (if fitted).

Listen to this man, he's right!

Also, this is a nice and clean rev 1.3 A600 miggy board, you should try your best to find out what's wrong with it, or get it fixed by someone on these forums.

EDIT: Nice timing, Akira
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Old 22 March 2012, 09:59   #24
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In the second bottom photo, the top row of pins on U14 and U36 look corroded to me.

Measuring the PSU voltages with no load, (amiga disconnected), is no problem. AFAIK, amiga psus have nothing similar to the ATX load sense thing. This will at least tell you if the correct voltages are present with no load. I would do this first before connecting a suspect PSU to an amiga for testing. If these are OK, then connect the amiga and measure again to see if they are too weak to power the board or maybe the board itself has a power fault.

For measuring voltage with the mobo powered on I don't like to poke into the actual power connector, too easy to short them out. I hold the black probe onto a ground somewhere. The big square pads where fixing screws go through are good. Then measure the voltages at the floppy or LED connector pins. You need to find another point to measure -12V as it is not present on these connectors.

IIRC +-12v are present on one side each of D576 and D575. These are the orange coloured cylinders also visible in your second bottom pic. Beneath the large electrolytic cap beneath the serial port connector. Just touch the red probe to one side of one of these at a time.

Good luck, whatever you do, don't bin it!
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Old 22 March 2012, 10:06   #25
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i think cosmos was selling caps for all amiga models for about 6 quid on ebay a few months back.

then you just need to find someone to do the cao replacement,thats if you cant do it yourself.
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Old 22 March 2012, 11:14   #26
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You should add some raw lemon juice (yes you read it correctly) to the capacitor pins and areas where you see non-shiny greenish pins. This will help a bit on the corrosion before desoldering. Also apply a new dose of lemon juice after desoldering. Be very careful -- corroded solder pads (and clean pads for that matter) are very fragile. Do your job as quickly as possible, rather than spending a lot of time on heating up the solder.

I understand if I talk like you were going to do this yourself, but this is also some advice that repairsmen could pick up regarding corrosion.
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Old 22 March 2012, 12:00   #27
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I'd send it to d0pefish and be done with it. I am pretty sure it's a capacitor problem.
Look at the fantastic job he did to my A600!: http://eab.abime.net/showthread.php?t=63156
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Old 22 March 2012, 19:29   #28
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On the multimeter settings suggested by Akira (20 DVC) I get a flickering of 0.00 to 0.01 when holding black (pluged into com) tocuhing the square metal outside bit and the red (plugged into VmA, just above com) touching +12v, +5v and -12v pins.
I then plugged it into the mobo and tested floppy connector only. Got nothing at all from that.
Please can you advise further. It'll be a shame to lose this cute little A600.
Cheers
Tony
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Old 22 March 2012, 20:59   #29
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Quote:
Originally Posted by trydowave View Post
On the multimeter settings suggested by Akira (20 DVC) I get a flickering of 0.00 to 0.01 when holding black (pluged into com) tocuhing the square metal outside bit and the red (plugged into VmA, just above com) touching +12v, +5v and -12v pins.
I'm not surprised that's all you get when testing the PSU in open-circuit conditions. I have experienced the same thing when trying out a perfectly working PSU in the same way (but bear in mind that jimbob would disagree with me about this).

Quote:
Originally Posted by trydowave View Post
I then plugged it into the mobo and tested floppy connector only. Got nothing at all from that.
Now you're talking, but getting neither a +12V rail nor a +5V rail at the floppy power connector is still inconclusive. You really must test the voltages at the power input socket to tell for sure whether the PSU is faulty or not, IMHO.
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Old 22 March 2012, 21:27   #30
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Hi Prowler. Can you give me a detailed description on how to do that pls.

Thanx ever so much
Tony
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Old 22 March 2012, 21:41   #31
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if no-one dont mind me saying,plug the power lead into the 600 turn on the power supply then,

with your black lead on your multimeter(com)press it against the right lead on the back of the power socket in the 600.(second pic 5th post in thread)this should be ground

then take the red lead and press it on the lead on the socket just below where you will have the black one(this should be +5volts)

then take the red lead again and test the lead on the back of the socket on the left upper side(this should be +12volts)


hope this helps.
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Old 22 March 2012, 22:05   #32
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Quote:
Originally Posted by prowler View Post
I'm not surprised that's all you get when testing the PSU in open-circuit conditions. I have experienced the same thing when trying out a perfectly working PSU in the same way (but bear in mind that jimbob would disagree with me about this).



Now you're talking, but getting neither a +12V rail nor a +5V rail at the floppy power connector is still inconclusive. You really must test the voltages at the power input socket to tell for sure whether the PSU is faulty or not, IMHO.
I should have proclaimed YMMV of course but I think that when you plug in the psu to the amiga the outer shield is connected to the actual ground. Until this connection is made you cannot use the outer square shield of the connector as a ground reference, So, when not connected to the amiga, you must measure from the actual ground pin, (upper right in Akiras pic). Take care, if you touch two pins with one probe, you'll get sparks. not deadly ones, but not good for the PSU.

It's true that measuring elsewhere on the board isn't a sure sign that the PSU is faulty as any fault could be somewhere on the board. Just mentioned that because the -12 pin, on the inside, is kinda hidden away.

Last edited by jimbob; 22 March 2012 at 22:54.
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Old 29 March 2012, 22:49   #33
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Just tested the psu unpluged from amiga and switched on. I used to the black and carefully touched the tip of the ground pin. I then touched the tips of +12v, -12v and +5v with the red. My multimeter is set to 20 on DCV. I got slight fluctuations on the aforementioned pins from around 0 to 1.
Please can (anyone) advise further. Is it time to get a new psu?
Cheers
Tony
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Old 30 March 2012, 00:10   #34
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I'd say yes, I have three brick type psus here, they all measure the correct voltages when measured the way you describe. Plus the fact you get nothing when it's connected to the mobo. Not guaranteed though. Did you try measuring directly at the power connector inside? Some other things to consider -

Are you sure your meter works, test on a battery or something.

Does the PSU make any sound when on, ticking/hissing/humming/whining or maybe a short squeal when you switch it off.

Do you have an old pc power supply kicking about, they are pretty easy to adapt, I think there is a guide around here somewhere.
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Old 30 March 2012, 16:25   #35
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Hi Jimbob What bit on the mobo do i touch apart from floppy connections... i didnt understand the previous post regarding that. (i see no leads on the power connector for example).
The meter does work and ive tried it on a button battery and a AA.
I remember back in the day the squeal from my old amiga 500 psu. I get no sound at all here.
I have lots of old pc psu's lying about, but ive seen the diagrams on how to do it and to be honest it looks a little difficult. If its time to get a new amiga psu ill just buy one instead.
Cheers
Tony
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Old 30 March 2012, 16:33   #36
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if you dont feel comfortable doing the soldering,get another psu.

on the other hand,if you have a freind who is in the know ask them to remove the power lead from the dead amiga supply and wire it up to the pc one.and show them the wiring for it.
check to make sure the cables have the correct voltages to them,dont go by the colours in diagrams some are different.
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Old 30 March 2012, 16:40   #37
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In the top left of your second pic. The black square that is the rear side of the fitting that takes the square power connector. You can probe the PSU voltages on the legs that come out the back of that. They are not all easy to reach though. Don't worry about trying to probe the -12V there. If you don't have +12 and +5 it isn't going to work anyway.

Probably best not to mess with a pc power supply if you're not confident about connecting it up right. Just mentioned it as you could've tested the mobo without springing for a new PSU first.
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Old 30 March 2012, 16:52   #38
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Don't have people who can help on the pc psu...
Jimbob.. did what you recommended and got no voltage on any legs. I now believe that its dead.
Time to get a new psu me thinks....

Cheers everyone for ya help... much appreciated.
Tony
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Old 30 March 2012, 21:12   #39
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Sometimes you can hear the psu if you put it to your ear,it will be humming,that means you are getting power to it ,its a shame you don't have another A600 to test it.

I did get a USB 2.0 to SATA/IDE Combo Adapter to power a Amiga CD32 and it works..(I don't have a PSU for a CD32)
You can get the adapter from Maplin.It works cos it has the power connector for a ide drive like on a PC PSU and I just connect it to the CD32 power socket..
If you want more details I can give more..
This is the page i used to get it working.
http://www.ianstedman.co.uk/Amiga/am..._supplies.html

Last edited by spannernick; 30 March 2012 at 22:01.
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Old 20 February 2013, 12:43   #40
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Just coming back to this thread as I recently dragged out the ol’ A600 again to see if I could get it to boot. I stripped it, took out the ROM and reseated it. Cleaned all pins and connections with alcohol, blew out all dust and plugged in a proper A600 PSU (rather than the A500 one I used before).
Turned it on and I still get a black screen? I'm beginning to think that it will never live again. Do you think it's time to throw in the towel with this one? I read that the black screen communicates that the cpu is dead. Either that or you have no video.
I've plugged it into the TV via RF and composite so I don't think it’s that. If it’s the CPU! Well. The cpu looks like it’s soldered down on the MB. How on earth can I fix that?
I do have a multimeter. Maybe there’s some way to check if the powers running to it. The psu is fine.

Cheers
Tony
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