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Offline harmonicaTopic starter

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A600 voltage problem
« on: September 02, 2009, 02:21:56 PM »
Hi,
I've recently bought A600 from an auction. It was bare Amiga, only with rebuilt PSU from PC. When I plug it and turn on, it boots with no problems to Kickstart, waiting for a floppy insert. The problem is the floppy drive is dead. So I dismantled Amiga, tried to found out something, but nothing seemed obvious. I plugged out floppy drive from Amiga and tried to measure voltage on onboard molex. I found out there that instead 5 V is only 3.5 - 3.8 V. 12 V seems to be correct, it's around 11.5 V. Then I tried to power floppy drive not from Amiga but from another ATX PSU and it worked like a charm. It reads floppies, boots to game etc. The only issue was the keyboard doesn't seem to work except Ctrl+A+A. Caps lock is permanently on.

My first thought was that the floppy problem was insufficient voltage from PSU. So I rebuilt another ATX PSU, but the problem is still the same. Even if I load the PSU with two HDDs. If I measure voltage directly from PSU, it's 4.8 V. If I measure voltage from onboard molex in Amiga it's 3.5 - 3.8 V and it's just too low to power the floppy drive. So any ideas? I checked capacitors with magnifying glass and it doesn't seem to be leaked.

Thanks for any suggestions.
« Last Edit: September 02, 2009, 02:45:02 PM by harmonica »
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Offline amiga1260

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Re: A600 voltage problem
« Reply #1 on: September 02, 2009, 03:00:33 PM »
You could try to find an A500 or A1200 PSU and test your A600.
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Offline harmonicaTopic starter

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Re: A600 voltage problem
« Reply #2 on: September 02, 2009, 03:38:08 PM »
Yeah, I probably will try. The interesting thing though is the decrease of voltage. I'm not sure if those capacitors near the power connector are used for some filtration. If they are, they might be going to fail. Nevertheless I'll try to look for some original PSU, but I'm not completely sure if it's going to help.
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Offline ferix

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Re: A600 voltage problem
« Reply #3 on: September 02, 2009, 03:42:24 PM »
Hmm... I think It could be a broken CIA (8250). They control the keyboard and some features of the fdd, like the motor on/off...
But I don't know how to test It on an A600.

Good luck!!

Edited:

The 12v line seems to be Ok, 11,5v is near from normal. The 5v line is too low, may be It affected to the CIAs.
Also, a broken chip could be a "power muncher"...
« Last Edit: September 02, 2009, 03:46:41 PM by ferix »
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Offline harmonicaTopic starter

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Re: A600 voltage problem
« Reply #4 on: September 02, 2009, 03:53:42 PM »
I don't know. As I said when FDD is powered from external power source and not from Amiga it works flawlessly. Everything is OK except the keyboard. I'd rather suspect some powering issues. Maybe even the keyboard has insufficient voltage.

Quote
he 5v line is too low, may be It affected to the CIAs.
Also, a broken chip could be a "power muncher"...        
Well after a few minutes every chip gets warm a little except Gayle. That is cold, but I have nothing connected to IDE...

EDIT:
If the problem would be caused by those CIAs, is there any way to test it if it's real cause?
« Last Edit: September 02, 2009, 04:13:59 PM by harmonica »
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Offline ferix

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Re: A600 voltage problem
« Reply #5 on: September 03, 2009, 07:49:20 AM »
Quote from: harmonica;521853
If the problem would be caused by those CIAs, is there any way to test it if it's real cause?

Sorry, I don't know how to test It on an A600... On an A500 you can swap the CIAs or even remove them, but A600 has them soldered. So, I'm planning to desolder all soldered customs in my A600 and put some sockets in place...
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Offline gertsy

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Re: A600 voltage problem
« Reply #6 on: September 03, 2009, 07:56:58 AM »
I was going to suggest the CIA swap, but didnt realise they were surface mounted on an A600 cost cutting huh..

Gertsy
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Offline spirantho

Re: A600 voltage problem
« Reply #7 on: September 03, 2009, 08:20:27 AM »
Change the caps. You should probably do this anyway, but the caps govern a lot of the voltages and don't usually last much longer than this anyway.
If your +5V line is so low I'm surprised the machine is working at all to be honest!
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Offline harmonicaTopic starter

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Re: A600 voltage problem
« Reply #8 on: September 03, 2009, 11:22:23 AM »
OK guys, thanks a lot for your ideas. I've put together TODO for myself:

1) Get original Amiga PSU
2) Measure if capacitors charge to voltage according to their specification
3) If not, replace capacitors
4) If it won't help, probably so long Amiga

Ad CIAs - as ferix says if it controls FDD motor I'd guess CIAs are OK because FDD motor works properly when it's not powered from Amiga while the ribbon cable is plugged in Amiga. I know Vesalia sells these 8520, but I don't feel myself so handy to replace them.

By the way interesting thing is when FDD is powered from Amiga as it should be, it doesn't work, but when I turn the PSU off FDD clicks and it rotates quarter of a rev. I'm not completely sure, but this behaviour could really imply capacitors problem rather than FDD controler.  I'd wish...

It may take some time to me. Nevertheless I'll inform you.
« Last Edit: September 03, 2009, 12:25:50 PM by harmonica »
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Offline ferix

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Re: A600 voltage problem
« Reply #9 on: September 03, 2009, 11:57:55 AM »
I suggest you replace the caps first.
It's cheap, and It's worth trying.
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Offline rkauer

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Re: A600 voltage problem
« Reply #10 on: September 04, 2009, 12:09:11 AM »
You can also check the power connector and filter section.

 A bad contact will lower the more-than-necessary +5V rail. Check the toroid coils for bad solder, too.

 Replacing capacitors on the A600 is always advisable, anyway. Do it.
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Offline harmonicaTopic starter

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Re: A600 voltage problem
« Reply #11 on: September 06, 2009, 04:56:35 PM »
So, I've found interesting thing. When I measure voltage on the plug that goes from my rebuilt ATX PSU between +5 V and GND it's 5.11 V. When I plug it to Amiga and measure voltage on the back side of motherboard where the power connector is soldered I measure only 3.8 V (GND <-> +5 V). So it seems it could be caused by the power connector or maybe some problems with grounding. Is it necessary the shield pin of power connector to be plugged?

EDIT: Between GND of PSU and GND of Amiga is 0.6 V.
« Last Edit: September 06, 2009, 05:04:35 PM by harmonica »
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Offline rkauer

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Re: A600 voltage problem
« Reply #12 on: September 06, 2009, 07:22:05 PM »
The shield pin is not necessary, and even is advisable to not use it.
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