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Old 23 September 2011, 06:42   #1
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Try repair an a4000 motherboard - help

Hi all amiga lovers,

I have an a4000 motherboard that has some strange problems.
I have detach all stuff not in case any longer.
I have old rom 3.0 and odd ramsey and or buster but have others it's only for test atm.

My working conditions:
CPU-Floppydrive (df0+df1)
CPU+Floppydrive (df0+df1)
Test of HDD an FDD floppyes operation was working too.
and with ofcourse a monitor so I can see something.
(CPU card test is a3200/a3400 and a3640 rev3.1)

Problem cases:

Case 1:
When I connect the a4000 keyboard, it gives me no boot
it just gives me grey screen and keyboard caps lock does not light up.

Case 2:
Another is when I attach to port 1 a mouse I can enter Amiga Early Startup Control but I can not use the mouse

Any clue what to do next?
So what advices are next to try out?

Would change of the 8520 chip help me out of these problems on u300 and u350 ?

Last edited by TTD; 24 September 2011 at 14:45. Reason: Case problems, more info
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Old 23 September 2011, 10:24   #2
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yep i think you hit the nail on the head there,try replacing the 8520.
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Old 23 September 2011, 12:05   #3
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Try to inspect Paula too. Turn on the unit, let it stay on for a while, try to feel with your fingers if either Paula or any of the CIA chips are getting suspiciously warm. Also look for capacitor leakage (tint of bluegreenish corrosion on metal) or battery alkaline leakage.
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Old 23 September 2011, 12:21   #4
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One of the tiny SMD chips next to battery is mouse/joystick port shift register (that connects to Lisa. Paula only have 2nd/3rd button IO ports). That chip's legs or PCB trace is one of the common parts that get destroyed by leaking battery.

It is not Paula. It probably isn't CIA either. It may be CIA if pressing left mousebutton has some effect. It may be Paula if right (or middle) mouse button has some effect. Mouse counters are inside Lisa (or Denise).
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Old 23 September 2011, 16:52   #5
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Thanks to all for help and inputs, to follow up on this.

Battery is not attached to the motherboard, if I have turn it on.
I can feel 2 chips components get more warm/hotter (but not suspiciciously) than others is 8374 alice (denise?) and 8364 (paula?) chip.

They just get hotter more warm than others not very hot can I do something to found out excatly if the need to be exchanged.

I have also looked around and the place called u177 smd chip number hct174a - xxaa336 from motorola the legs and pcb trace does not look good.
Now comes the tricky part how do I get that component and how do I repair it?

I have something for soldering and or multimeter, but these lines is so small and my station is not that small, can I confirm some kind of contact.
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Old 23 September 2011, 20:07   #6
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Paula and Alice do get quite hot in a matter of minutes, it's normal.
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Old 23 September 2011, 21:50   #7
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check big round yellow fuse ...
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Old 24 September 2011, 14:48   #8
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Quote:
Originally Posted by bebek View Post
check big round yellow fuse ...
do you mean that one called vc190? how can I check that

Note: @bebek tells me it's yellow (fuse) but mine is blue and it's marked on F175, the only yellow I see is marked on potition I have written, therefore I was confused at that, I was focus more at color than other word as fuse.

Last edited by TTD; 25 September 2011 at 01:37. Reason: Note info
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Old 24 September 2011, 15:56   #9
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Quote:
Originally Posted by TTD View Post
do you mean that one called vc190? how can I check that
If you're not sure how to check a fuse then might I suggest you send your Amiga to someone with some technical knowledge to get to the bottom of your issues.
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Old 24 September 2011, 16:32   #10
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Quote:
Originally Posted by TTD
I have also looked around and the place called u177 smd chip number hct174a - xxaa336 from motorola the legs and pcb trace does not look good.
Can you take a picture?
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Old 25 September 2011, 01:11   #11
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Quote:
Originally Posted by Loedown View Post
If you're not sure how to check a fuse then might I suggest you send your Amiga to someone with some technical knowledge to get to the bottom of your issues.
That is not a possible solution at the moment if I had enough money allready, why do you thing I ask in here because I have alot of money?

Then I would not try learning about repair it self.
When I dont have the money so try it with help from other this reply is useless for me.
That was a solution if I had enough money but I dont, so if you want to help, fine if you can't come with other than that, please do not reply thanks else all other info is acceptable.

Quote:
Originally Posted by 8bitbubsy View Post
Can you take a picture?
Well I could take a picture if I had the camera or cell phone but not an option, atleast a good suggestion so other could see it, and maybe fine the spot.

Last edited by TCD; 25 September 2011 at 01:29.
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Old 25 September 2011, 04:39   #12
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Quote:
Originally Posted by TTD View Post
That is not a possible solution at the moment if I had enough money allready, why do you thing I ask in here because I have alot of money?

Then I would not try learning about repair it self.
When I dont have the money so try it with help from other this reply is useless for me.
That was a solution if I had enough money but I dont, so if you want to help, fine if you can't come with other than that, please do not reply thanks else all other info is acceptable.



Well I could take a picture if I had the camera or cell phone but not an option, atleast a good suggestion so other could see it, and maybe fine the spot.
There's no need to be rude and I might further add that people are here for all sorts of reasons and ask about all sorts of problems, their financial status doesn't come into it. If you don't know how to test a fuse then you are not going to know how to test anything more complicated.
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Old 25 September 2011, 05:02   #13
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Quote:
Originally Posted by TTD View Post
That is not a possible solution at the moment if I had enough money allready, why do you thing I ask in here because I have alot of money?
But as computers age, things go wrong with them that might be a simple open fuse, which needs more specialized technical skill at finding, and repairing, something that needs a few monetary values.

For instance, Audio circuit capacitors, which when leaking (or about to leak) do not show a simple open circuit like a fuse, but in fact plays havoc with their capacitance, which throws the entire associated circuit in to chaos.

So really, if the ability is not there to even check the state of a fuse, how do you think you would cope with more complex fault finding ?

In fact as it happens, I have sought the help of Loedown with the repair of my 4000 Audio circuit, he knows what he is doing. (Oh and Loedown, my 4000 still happily sings away )
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Old 25 September 2011, 05:55   #14
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Quote:
Originally Posted by Loedown View Post
There's no need to be rude and I might further add that people are here for all sorts of reasons and ask about all sorts of problems, their financial status doesn't come into it. If you don't know how to test a fuse then you are not going to know how to test anything more complicated.
Well rude is your opinion I try repair something, you discuss other things, you maybe have right, I can not test anything more complicated but you dont show it other than how weak I'am trying fix an a4000 motherboard - and maybe I don't have enough knowledge to it, but then I have tryed.

I don't say I have all knowledge allready and/or skills with me, this could also be a learning process for me, and sure it's.
I'm willing to learn, do you want to try help explain or do you want to discuss about rudeless, financially and so on, you need to begin somewhere, right to troubleshoot?

Did you read my edit on post where I ask to check, the user did write yellow fuse, which I was to much focus on the color?

Have made a notice, I was focus on color not the fuse on the motherboard and maybe tell where I could find it? (You could give advice like what is F175, maybe - that would indeed have help, what does mean that F indicate on motherboard, maybe I could ask that and learned, could it maybe be the fuse?)
If F175 is not the fuse then, ok - then I don't know what it's and maybe should stop further process, but atleast learn something.

I also did write something about vc190, and here I have no idea what that is.
So why do you reply to a thread I have started and this is what your suggestion is.
If you don't try explain I cannot improve, if I do read something wrong, because my lack of english - then it might be a problem too.

Maybe we should have this clear out what do you think I mean "try repair an a4000 motherboard - help."

But I still not mean you try help me further just give me some kind of extra problems with try explain everything for you, and tell how weak I'am because I don't know where the fuse is or how I can test it.

Do you think this improve anyone try fix something that you never have try before done on a4000 motherboard, so sorry I ask but who is rude?

I ask for help, I don't expect to be helped, you must surely have some ideas or know something about it, but for me it looks you dont want to tell it, so is this bring my trouble shooting further, technical no, or do I waste my time try replying here to your inputs.

Maybe it's time for me to ask you personally what do you think there is wrong with it?
Are you self an technical expert on a4000 motherboards?
and can test more complicated things for yourself?

Because I have an idea what is wrong with it but how can I fix/repair it.

New Edit:
Since I read @whiteb's post after my reply to you.
I must say it would have being better if you have told me that yourself that you are expert, and not hide your skills, but you don't want to show it, you proparly have your reasons for doing so.
Other try get things more complicated but then try reply what is wrong with motherboard I have an idea it might be wrong but what do I noob like me know about this.
A pm could have clear more things out for me in this situation, but I still have that oppinion on it even with your skills you could say nice that you try but that will not have piss me off.

Last edited by TTD; 25 September 2011 at 06:29. Reason: Because of replying to one post then new was coming
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Old 25 September 2011, 06:01   #15
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Quote:
Originally Posted by whiteb View Post
But as computers age, things go wrong with them that might be a simple open fuse, which needs more specialized technical skill at finding, and repairing, something that needs a few monetary values.

For instance, Audio circuit capacitors, which when leaking (or about to leak) do not show a simple open circuit like a fuse, but in fact plays havoc with their capacitance, which throws the entire associated circuit in to chaos.

So really, if the ability is not there to even check the state of a fuse, how do you think you would cope with more complex fault finding ?

In fact as it happens, I have sought the help of Loedown with the repair of my 4000 Audio circuit, he knows what he is doing. (Oh and Loedown, my 4000 still happily sings away )
@whiteb I thank you for tell me that is surely a reply that is acceptable and if he knows it, why did he not show it more with tell where fuse is, sorry. But funny the fuse has been replaced allready if it was f175, if not then no fuse change.

I have try looking a bit more on my keyboard case 1: it must have been something to do with keyboard clock and keyboard data as this might be a wild guess when I say u205 74hc4066 ic, u141 sn7407 is maybe the kbdata, if is locked it has proparly something to do with u131 sn7405, is there any one there can confirm this and would an expert be nice to tell if they know what price are for these chips.

Case 2: about mouse - the thing I guess again maybe a wild one is have something with u925 and u926 the small smd has this number 74htc166 on both. Would also be good if anyone can confirm it and might have an idea of price for such electronic components.

Last would it help if I exchange these maybe get more live to my amiga and will it fix thoese problems get away, so I can continue find more if any or maybe is all done, now if this can be made I must try figure out how is it possible for my low soldering skills to do this or maybe an idea of the cost for a professional to do that job.

Last edited by TTD; 25 September 2011 at 11:15. Reason: Just to clear more things out
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Old 25 September 2011, 13:59   #16
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Your problem is that I wasn't being rude in the first place I was being absolutely honest and some people don't like honesty.

Testing a fuse is the simplest thing to do, it's a conductor which is either open circuit or short circuit.

I haven't replied in this thread apart from adding a few small things because it became obvious that you have no idea about what you're doing or checking or looking at and anything I had to say would have been pointless. I gave you the best answer for your problem in that take it to a technician who would have been able to help.

Case 1: Keyboard.
It sounds like the keyboard you have is faulty, for a keyboard to stop an Amiga from booting suggests that it has a real problem and this is most likely what has fried some of the further circuitry. You also need to verify the power supply isn't being dragged down by a short or failing because of an overload if it is indeed the original and not an ATX style one.

Case2: Mouse
My A4000 was originally owned by a chap who has since shuffled off this mortal coil, but whilst he was alive he also had an issue with the mouse not working properly and it turned out to be one of the logic chips which he replaced and I subsequently resoldered and cleaned up for him.

Fixing any electronic device requires logic and patience, not randomly swapping this and that to see if there's a sudden flash in the pan solution. It also helps if you own a multimeter at least and preferably an oscilloscope.

I have not made you feel weak, although you yourself have made yourself look stupid and going off on a rant isn't going to make people want to assist you at all, now or in the future.

Surface mount repair isn't something you just do willy-nilly, it's a skill and requires some practise so that you don't destroy your rather hard to find A4000 mainboard, another reason why I suggested you take it to a technician.


@Whitby: Good that the machine is behaving itself, with regular use it should continue to be that way for many years to come.

Last edited by Loedown; 25 September 2011 at 14:00. Reason: typo
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Old 25 September 2011, 17:43   #17
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Quote:
Originally Posted by Loedown View Post
Your problem is that I wasn't being rude in the first place I was being absolutely honest and some people don't like honesty.

Testing a fuse is the simplest thing to do, it's a conductor which is either open circuit or short circuit.

I haven't replied in this thread apart from adding a few small things because it became obvious that you have no idea about what you're doing or checking or looking at and anything I had to say would have been pointless. I gave you the best answer for your problem in that take it to a technician who would have been able to help.

Case 1: Keyboard.
It sounds like the keyboard you have is faulty, for a keyboard to stop an Amiga from booting suggests that it has a real problem and this is most likely what has fried some of the further circuitry. You also need to verify the power supply isn't being dragged down by a short or failing because of an overload if it is indeed the original and not an ATX style one.

Case2: Mouse
My A4000 was originally owned by a chap who has since shuffled off this mortal coil, but whilst he was alive he also had an issue with the mouse not working properly and it turned out to be one of the logic chips which he replaced and I subsequently resoldered and cleaned up for him.

Fixing any electronic device requires logic and patience, not randomly swapping this and that to see if there's a sudden flash in the pan solution. It also helps if you own a multimeter at least and preferably an oscilloscope.

I have not made you feel weak, although you yourself have made yourself look stupid and going off on a rant isn't going to make people want to assist you at all, now or in the future.

Surface mount repair isn't something you just do willy-nilly, it's a skill and requires some practise so that you don't destroy your rather hard to find A4000 mainboard, another reason why I suggested you take it to a technician.


@Whitby: Good that the machine is behaving itself, with regular use it should continue to be that way for many years to come.
-

@Loedown I must say I preffered honesty. I'am happy over that you even reply this way instead, and with your knowledge of these technicial skills, I take your advice more serious, with showing with such info like this.

Well I have self through on my psu to my amiga could be a problem too, which is quite easy to swap on normally PCs, I also use an original a4000psu.

I must then say the keyboard, well I could try change it, because I have one working a4000. I could test these on that and see if that was the reason. So this is my next step to do, if they working then good.

But what if this case is that I think +5v have got -5v rail, and -5v got the +5v on the motherboard.
I know surface mount would not be something you do as a beginner in try fixing without much soldering knowledge at all, and need some kind of special skill and/or equipment.
I also like your explanation with the cases.
I also thing this repair is absolutly not possible for me to repair on my own and need an expert to do this.

Then I will only ask, is this something with your skills can repair and have you any clue what it will cost, if it was you there should repair it?

The multimeter - I have test the fuse with it, the multimeter I use is make a high pitch sound, in open circuit.

Yes, sometime I just act stupid that is maybe a bit I do this and will proparly not help me further, maybe it will not get me much help in future too, but that is general my problem.

Last edited by TTD; 25 September 2011 at 17:49.
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Old 25 September 2011, 21:36   #18
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Originally Posted by TTD View Post
do you mean that one called vc190? how can I check that

Note: @bebek tells me it's yellow (fuse) but mine is blue and it's marked on F175, the only yellow I see is marked on potition I have written, therefore I was confused at that, I was focus more at color than other word as fuse.
sorry it is F175 - all mine are yellow , they are easy to snap so check if it is still connected to the mainboard
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Old 25 September 2011, 22:30   #19
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Quote:
Originally Posted by bebek View Post
sorry it is F175 - all mine are yellow , they are easy to snap so check if it is still connected to the mainboard
bebek, that confirmed just that I was focus more on color
I have a spare one - there is yellow or might called orange, but ok, now I know what I am looking for and where.
I also did confirm that I have found it, that do help alot, anyway thanks.

Maybe a bad example: Another one could be try exchange one of the intrigated chips on the a4000 motherboard, but there is alot.
A hint would also make it more easy to locate if I know the u number, I proparly know what few u number is, but not all.

Since the technical guy that have proparlly right I need to goto a professional with it, then I can maybe better describe what I have tryed to repair or locate the problem.

The keyboard what he suggest a good logical idea, is also have been tested on my other a4000 that works - the keyboard works there.
The mouse to see if that did work to, have been tested on my a500+ and works there just to get it more cleared what is tryed and what is not tryed out.

I just think I get small step further and that is to begin with alot for me.

I thank all for all there help they give and ideas.
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Old 26 September 2011, 10:45   #20
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Originally Posted by TTD View Post
-

@Loedown I must say I preffered honesty. I'am happy over that you even reply this way instead, and with your knowledge of these technicial skills, I take your advice more serious, with showing with such info like this.

Well I have self through on my psu to my amiga could be a problem too, which is quite easy to swap on normally PCs, I also use an original a4000psu.

I must then say the keyboard, well I could try change it, because I have one working a4000. I could test these on that and see if that was the reason. So this is my next step to do, if they working then good.

But what if this case is that I think +5v have got -5v rail, and -5v got the +5v on the motherboard.
I know surface mount would not be something you do as a beginner in try fixing without much soldering knowledge at all, and need some kind of special skill and/or equipment.
I also like your explanation with the cases.
I also thing this repair is absolutly not possible for me to repair on my own and need an expert to do this.

Then I will only ask, is this something with your skills can repair and have you any clue what it will cost, if it was you there should repair it?

The multimeter - I have test the fuse with it, the multimeter I use is make a high pitch sound, in open circuit.

Yes, sometime I just act stupid that is maybe a bit I do this and will proparly not help me further, maybe it will not get me much help in future too, but that is general my problem.
I did reply honestly to start with, the repair was never going to be one that could be carried out with limited knowledge.

FB177, Ferrite Bead 177 located on mainboard top side needs to read 0 ohms or short circuit, usually the beeping on a multimeter means you have it on diode setting and it's reading somewhere around zero ohms.

When the unit is powered on you need to see +5 V on that ferrite bead with keyboard plugged in. No +5 V means that the main power connector could have one pin that has pushed back into the shell.

ER175 and ER176 located on bottom side need to read around 47 ohms.

These are the basic things to check.


From looking through the schematics both keyboard and mouse use +5 User rail, I would look at this and make sure it's supplying +5 V, I am almost certain this is the problem, no mouse functions and no keyboard functions / no caps lock light.

You can send the board to me if you like but the postage costs from Denmark to Australia would be horrendous.
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