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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Gwion on May 03, 2008, 07:09:42 PM
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I opened my A3K today to replace its HD. I took the LEDs off to re-solder them.
I put the put the LEDs on when the machine was on then the connections of the HD led hit the metal case of the machine and it sparked then the machine went off.
The PSU powers when not connected to the mobo but when its plugged into the mobo it doesnt power.
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rework is needed, send the motherboard to JJB at Amigacenter.
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I think there is a transistor driving the LED on the A3K, its probably gone open circuit, find the transistor and change it.
I have to say Ive been lucky as Ive shorted most of my Amiga's against the case one way or another and after an hour max the machine turns on and is fine, guess Ive just been lucky :)
EDIT----
Ok after looking it was a 7407 and it was resistor protected.
But it seems they didnt protect the 5V power.
it goes 5V+ ---- LED ---- resistor ---- 7407 chip.
So if you shorted the 5V to ground then it was a direct short, check if the PSU is outputting 5V still and then check a chip to see if its getting 5V.
There is no fuse protecting the main 5V line from what I can see.
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Disonnect the HD/Power LED's from the motherboard and see what happens.
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Oh i'll leave it for a hour then i'll check of disconnecting the HD/Power LEDs will fix it.
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Got bored of waiting for a hour so i tried the PSU on the mobo abit loose and the A3K boots.
But when i put it on fully it doesnt :-?
Any ideas?
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Take the mobo out (I know, it's an a lot of work) and clean underneath it. Seems like your mobo may contact with the chassis. Also, you might first try cleaning the connector with contact-cleaner and tighten the bushes a bit.
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Ok will do
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Also check if one of those pins in the power connector had not coming loose from the motherboard (cold joint).
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Took out the motherboard no cold joints.
Connected my A2000's PSU to the motherboard and still the same.
Dont know what else to do.
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Oli_hd is right. The 7407 (U352, an inverter) switches the ground side of the LED through a 56 ohm resister (R300). The cathode is tied directly to a branch of the +5V rail.
Can you get your hands on a meter and check the power supply for +5V? Check the little board with LEDs for +5V? Check where the wires from that board ties to the MB? Check this branch all the way to where it is supplied with +5V by the Power supply connector? If you burned out a skinny +5V trace that supplies the LED and several chips, you will have to solder in a new wire to re-supply this branch with +5V.
It's sorta like heart bypass surgery. Grin.
You didn't put the LED in backwards?
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Accident :-(
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Let us know how this goes. I think this is repairable.
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I replaced the PSU and guess what?!?!?
It doesnt work!!! :madashell: :madashell:
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only Joking it fixed it :-D
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Congratulations :-)
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Oh it kinda works its just the floppy driv the doesnt even when a external one is connected. The LED on the floppy drive is constantly on.
Any ideas on how to fix it?
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Change Paula and CIA...
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So if i replace them it should work? Will ones from a A500/+ work?
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Gwion wrote:
Oh it kinda works its just the floppy driv the doesnt even when a external one is connected. The LED on the floppy drive is constantly on.
Any ideas on how to fix it?
Sounds like the floppy cable might be in upside-down or something. Double-check, or try with another cable?
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Sounds like the floppy cable might be in upside-down or something. Double-check, or try with another cable?
Yep i've tried that but still the same and the external drive should work even if that happened
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Again: change CIA and Paula.
You can swap 'em from any other from A1000 to A3000 versions! The CIAs are different only in A600/1200/4000/CD32 (SMD versions).
And you can buy replacements from Amigakit or Vesalia. They have the chips in stock.
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Oh i just remmembered when i plug the +12V into the amiga 3000's mobo it doesnt power, Any reason why this might be happening? I think its might controller the disk drive stuff?
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Gwion wrote:
Oh I just remembered when I plug the +12V into the Amiga 3000's mobo it doesn't power, Any reason why this might be happening? I think its might controller the disk drive stuff?
Not exactly. The 12V line is used only in the audio circuit and to feed the termination rail for SCSI devices.
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SO what can i do to fix the audio?
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Replace Paula.
Check the electrolytic capacitors (swap 'em). Also look for burned traces, bad fuses and, specially, bad SCSI cables (nothing to do with audio business, but the problem can be on it).
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I replaced the CIA's and now the floppy drive works!
But i did 'kill' one CIA by trying the +12V when i got the floppy drive working. The the floppy drive didnt work again untill i replaced the CIA (one nearest to the back of the machine)
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So buy a spare A500 mobo for take the spare CIAs, Paula, etc..
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Ok audio kinda works its just sound quiet andis low quality when at a reason able volume
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How much voltage will the audio need? And why do u think the system wont start with the +12V?
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The audio circuit needs +12 and -12V to work.
Reliable operation is in 10.5~12.1V range (symmetric to the negative line).
Distortion in audio indicate bad audio decoupling capacitors. Namely C433 and C443 in big-box Amigas. 22uF x 16V. Prefer swap 'em for no-polarized version. Using regular, polarized versions is a project error in the Amiga boards!
Also Paula can be involved in the audio problem, since she is the responsible for sound generation (among other things).
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It got worse i was playing lemmings then i smellt something burning. It was one of the CIA's the one closest to the dauhterboard! I removed it and put anotherone in and same thing happened te CIA went boiling and i have them in the right way. It booted to a white/grey screen for a while now it
boots to a green screen. Now what could be the problem.
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BAD PSU!!! Check it before anything else!
BTW: your CIA have gone south, a this time.
Don`t trust on what you read from a multimeter with the PSU out of the board (no charge). Prefer to swap it for a newer unit, like an AT/ATX one converted (you need to swap the JP350 jumper position to use a PSU without the "tick" signal).