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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: mfrank on October 19, 2008, 06:46:28 PM
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I have an A4000 that had the battery removed long ago, however, while I was using it the resistors leading to the serial port are overheating and burning, they are R993,994 and 989, since these are right next to the battery I'm assuming that old leakage caused the problem, My question is, if I cut the resistors out (carefully) the worst I could do is to disable the port, (that should eliminate the short) I would still have the other port for the mouse, any help is greatly appreciated, also did I read the schematic right? Also if I killed both serial ports will an add in card with serial ports work for the mouse - the lesson here is to clean around the battery if you remove it.
Thanks Mike
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questions like that will be usually best answered on a german site a1k dot org. they have international section even when it isnt frequently visited
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Charming ... we'll just stop helping people and let a1k.org do it all shall we? :lol:
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If you mean the 2 9-pin ports on the side of the machine, those are the mouse and joystick ports, not serial ports. You need them both, as I don't think mice usually work properly in the joystick port.
Ancient serial mice can be connected to the actual serial port with the help of a driver, but they don't work with non-system-friendly programs.
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Yes I meant the mouse and joystick ports, my brain stopped working when I realized I had the problem, I also realize that I have the Rev. B motherboard and the old battery was between the simms and the row of 8 resistors where I'm having the problem, I noticed that the trace from one side of the resistors goes to the J975, "the mystery jumper" so if I replace the resistors I can make one side of the connection there and avoid the motherboard. Thanks for the help, Mike
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The resistor designators you mentioned have a value of 4.7k Ohm. They're size 1206 SMD resistors, which are rated at 1/4W. To exceed their power rating and overheat, you'd need a voltage greater than sqrt(0.25 x 4700) = 34.3V. Given the fact the computer runs on 5V, it's unlikely that this is happening.
Are you sure it's not a problem with any of the latches or shift registers in that area? Battery corrosion can do some nasty things to PCB tracks and semiconductors. It's usually best to replace the devices which have been corroded and clean the PCB up properly. The corrosion extends well under the surface mount ICs and corrodes the copper vias hidden underneath, so ideally this should be cleaned properly.
I've written plenty of information on this sort of thing here (http://amiga.serveftp.net/hardware_repair.html).
The circuit which operates the shift register to drive J975 is still needed, as the system polls it during power up to check if AGA mode is supported by the board. Input bits 0 and 1 are tied permanently high, so if the system cannot see U976, then you'll find only ECS screenmodes will be available.
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Not sure if this is related, but my A4000 has decided to not boot. on power up, i get a flashing power light, and nothing on screen. then then machine seems to reset, and goes through the whole flashing power light thing again.
no flashing caps lock light to maybe hint at whats going on.
the battery had been removed before i got the machine, and from what i can tell, it's been removed for quite some time. the only hint of life i got out of it yesterday was when i removed and refitted all the simms. i got one clean power on self test, then setpatch rebooted the machine as per OS3.9, and then flashing powerlight of doom. i've swapped simms around, wiggled things pushed things into sockets, held the simm modules in, but i can't get anything to work.
i'm hoping that there isn't some battery acid on/in the board somewhere eating away at things. :-(
anyone got any ideas? :-?
its the board revision with the 5 cheap simm sockets, one for chipram, and four for fastram.
so far, i guess i'm asking for a hot air re-work tool for xmas ;-)
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A slightly more expensive solution is to send the A4000 mobo to the Amiga Repair Centre in France. JJ B does an excellent fixed price repair. Not only does he fixed clock ports he also repairs mouse ports and leaky Audio caps. He also has a fix for broken Memory Simms clips.
I'm not that confident with the soldering iron and have used his service to repair a number of battery damaged A4000 mobo's.
Good luck.
TrevorD
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thanks Trevor, i'll certainly bear that in mind! i'd forgotten about ARC France... :-)
but i'm kinda hoping there is something i can do before i have to send it away :-(
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I'll second Trevor's recommendation for the Amiga Repair Center. JJ did an excellent job getting my A4000 back. I'd lost audio and the par: port to battery damage. JJ refurbed the main board and processor card and installed a coin style battery to replace the old one.
Great work! I'd recommend him anytime. Since you just send the motherboard it reduces the cost of shipping.
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FWIW, all of my boards from that era have leaking caps. I started removing some from an A1200 motherboard yesterday, and there were a few that had very slightly damaged the PCB underneath even though they looked "good" externally. (I'm guessing minimal damage is probably inevitable if the leakage is clearly visible.) May not a bad idea to start there if they haven't been done.
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:-( cool ok. well, today it seems that something more terminal is going on. initailly this morning the machine wouldn't power on. the PSU fan spins and drives run, but nothing else. tested the PSU, all ok, swapped the PSU to double check. all ok. swapped back, but now i'm back to the continuous reboot and no screen thing again..
the cap near the RTC circuit has dull solder points. i have neither the skill nor the tools to repair. can i rock the cap untill it weakens the legs so it comes off before more damage occurs? :-? before sending off for fixing. (which will be a while as i have three birthdays, xmas, and new years to budget for :lol:)
as to what it is doing at the moment. when it does fire up instead of continous reboot, i get a red screen which means "bad rom" and if no screen is showing then i get a single capslock light flash, which translates as "bad rom checksum"
to further investigate, i swapped out the A4000 3.1roms with one of the many pairs of A1200 3.0roms i have laying around. i don't get the instant flashing power light, but i don't get anything else either except a continous power light. i guess a1200 roms arn't compatable with the A4000 :roll:
also checked another A4030 cpu board to be doubly sure. same thing as above...
i don't belive that roms can go bad on their own. so i guess its a caps issue :-(
--edit--
ok thats it, now at switch on, the PSU sounds like its under load (fan sounds like its not spining so fast) but no power light, no nothing. :crazy: :hammer: :crazy: :hammer: :crazy:
i give up untill i can get this sick machine packaged off for repair...
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Whenever I remove a battery I always use vinegar to neutralize the acid, I apply a generous ammount of vinegar and use a toothbrush to sort of brush off any lumps of battery acid. Then flush with water. I then use a spray originally intented to clean radio control car electric motors motors, which then displaces any water and evaporates leaving no residue. Then let dry for 24-48hrs just to be safe.
Using this process I have never had a problem.
Most of the time I replace the original battery with a GP Nimh, although you do not have to do this.
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Ideal wrote:
Whenever I remove a battery I always use vinegar to neutralize the acid, I apply a generous ammount of vinegar and use a toothbrush to sort of brush off any lumps of battery acid. Then flush with water. I then use a spray originally intented to clean radio control car electric motors motors, which then displaces any water and evaporates leaving no residue. Then let dry for 24-48hrs just to be safe.
Using this process I have never had a problem.
Most of the time I replace the original battery with a GP Nimh, although you do not have to do this.
My A4000 arrived with the battery removed, but evidence of leakage. It seems to have been cleaned, but there is a green discolouring to some of the metal components and I'm worried that it might still be residue from the battery rather than old corrosion from the leak. I should probably follow what you said just to be sure.
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darksun9210 wrote:
the cap near the RTC circuit has dull solder points. i have neither the skill nor the tools to repair. can i rock the cap untill it weakens the legs so it comes off before more damage occurs? :-? before sending off for fixing. (which will be a while as i have three birthdays, xmas, and new years to budget for :lol:)
I wouldn't try to wiggle it off! If you heat up one leg at a time, and very *gently* move the cap up a bit each side, it will eventually come off with no damage. Applying a little fresh solder to the corroded joints will really help. Just take your time, read Castellen's awesome guides (and posts from guys like da9000 who have done a lot of these), be extra cautious and you will do fine. :)
-edit- Actually, I think I am wrong on this. Gently moving the cap to the side of the pads (a small amount, one side at a time with one iron) is probably a better method (I believe this his how Castellen says to do it in his guide without hot air). Lifting a bit to get some fresh solder under the cap leg might be necessary for corroded/stubborn joints, but it seems lifting upwards, no matter how careful, carries a higher risk of lifted pads. :-o Especially on the little 10uf guys, and electrolyte damaged pads.
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right, i'm going to do the vinager thing to neutralise whatever is going on there and a rinse off.
i usually go for soya sauce rather than vinager on my chips...
then run a patch lead to skip over the eaten bit. hope this works ... :-)