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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: spirantho on July 18, 2012, 05:10:57 PM
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Hi people,
Still fighting my A4000.
Occasionally it boots, and I'm fairly sure now it's to do with the CPU connector. I've got the voltages up nicely, so that should be ok.
I've cleaned and re-cleaned the CPU connector but it's so bloomin' difficult to get at, I still can't be sure it's clean.
Anyhoo, the symptom at the moment is a bright magenta screen on a cold boot. I know the CPU is basically working because if I remove the chip RAM, then it sure enough boots to a green screen.
Very occasionally I get a white screen.
Quite often I get nothing at all - just a dark grey screen as though the CPU is doing nothing.
I've tried with both the original 030 module and the CS-PPC, same thing on both.
All this time the Caps Lock light works as it should, no error codes or anything there.
Anyone got any ideas? Thanks if so!
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By Magenta do you mean purple? Red = boot ROMs, Blue = custom chips, and Green = Chip ram. These are the initial colors on cold boot. Only OS 4.1 uses a light pinkish purple that I would call Magenta.
Could your monitor signal be set to clarify between Red and Blue?
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Hi people,
Still fighting my A4000.
Occasionally it boots, and I'm fairly sure now it's to do with the CPU connector. I've got the voltages up nicely, so that should be ok.
I've cleaned and re-cleaned the CPU connector but it's so bloomin' difficult to get at, I still can't be sure it's clean.
Anyhoo, the symptom at the moment is a bright magenta screen on a cold boot. I know the CPU is basically working because if I remove the chip RAM, then it sure enough boots to a green screen.
Very occasionally I get a white screen.
Quite often I get nothing at all - just a dark grey screen as though the CPU is doing nothing.
I've tried with both the original 030 module and the CS-PPC, same thing on both.
All this time the Caps Lock light works as it should, no error codes or anything there.
Anyone got any ideas? Thanks if so!
are you sure the chip ram simm is correct?
double checked all the motherboard jumper? move them on the pins in case they are tarnished and making bad contact.
are you booting with floppy and or HD? i assume you waited long enough for the insert disk screen, it takes forever with no ide etc hooked up.
can the caps lock key be pressed on/off and the light responds still after say.. 10 times?
mech
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I'll try the caps lock for longer when I get chance tomorrow.
It's the same magenta as when OS 4 boots, yes, but this is on a cold boot with just a floppy attached.
edit: it did work very occasionally earlier today but now it's just this magenta screen instead. The TV signal is displayed fine though.
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I'll try the caps lock for longer when I get chance tomorrow.
It's the same magenta as when OS 4 boots, yes, but this is on a cold boot with just a floppy attached.
edit: it did work very occasionally earlier today but now it's just this magenta screen instead. The TV signal is displayed fine though.
Hmmm? tv signal? is the 4000 hooked up using a A520 on the rgb port and then composite or are you hooking this to a big screen tv or some such via VGA?
Most tv's will not take 15khz in from the 4000 and display it over the vga port-they expect 31khz in most cases(there are exceptions) but could this be the trouble?
Mech
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On a positive note the fact that it occasionally works indicates a likely intermittent contact issue; often they work when things heat up and metal expands or when you wiggle or jiggle a part or connection.
So reseat EVERYTHING and if it is not shiny use a fine emery board to get rid of oxidation; I use an eraser on gold card connectors. For things like cables that feel loose, use a fine set of needle nose pliers to tighten Molex pins and such. There is also sold through cyberguys a Deoxit spray to improve contact.
With patience and changing one thing at a time you might ne able to define what is at issue -- not likely you CPU from your scenario, so look to the motherboard and connections there
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On a positive note the fact that it occasionally works indicates a likely intermittent contact issue; often they work when things heat up and metal expands or when you wiggle or jiggle a part or connection.
So reseat EVERYTHING and if it is not shiny use a fine emery board to get rid of oxidation; I use an eraser on gold card connectors. For things like cables that feel loose, use a fine set of needle nose pliers to tighten Molex pins and such. There is also sold through cyberguys a Deoxit spray to improve contact.
With patience and changing one thing at a time you might ne able to define what is at issue -- not likely your CPU from your scenario, so look to the motherboard and connections there
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Although an eraser can be used to clean connector contacts I prefer to use either contact cleaner or 99% Isopropanol Alcohol.
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Yes contact cleaner is best if you have it; Isopropal Alcohol will remove grease but does not reduce the oxidation. Acid will dissolve it (citric or acetic) and sulfite compounds will actively reduce it back to its metal base.
Intermittent contact issues might be caused by a failing capacitor.
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Well here's an interesting thing.
I just re-fluxed and re-flowed Fat Gary, Ramsey and U145, as well as using the contact cleaner on U103.
Not had a magenta screen since. In fact it's booted about 4 or 5 times with the A3630. Still no boot with the CS-PPC, and with the 3630 it often needs to be soft-rebooted after about 30 seconds of blank screen - which implies irregular voltage still. My +5V line has now been capacitated with Low ESR Rubycon caps, and the line is good at +4.96V. However, the -12V has fluctuation, and the +12V may have too, so I'm going to recap those lines too with posh caps....
Odd. I just put the CS-PPC back in and now both CPU cards have gone magenta again. Yet I'm pretty sure the CPU slot is ok now....
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Well it sounds like motherboard is fixable, you might have to get some work done on the CSPPC like replace a socket or some capacitors. I would make the CSPPC my priority (they are my best Amiga addition next to the Deneb)
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I've already done the CSPPC. :) I think it's fine but I don't have another 4000 to test with.
It's gone back to magenta screen again now. I've re-socketed U103 but no change.
I've noticed that eventually it does actually go off the magenta screen. It tends to go to a magenta/black combination screen as if it can't make its mind up what colour to go, and then returns to magenta again - or occasionally black.
Here's what just happened:
Power On -> Magenta screen -> *wait a few minutes* -> Magenta/Black striped -> Magenta -> striped -> Magenta -> (C-A-A Soft reboot a few times) -> Magenta -> Lined -> (C-A-A soft reboot) -> Boot normally.
Right now it's sitting there looking at me with a friendly looking disk being inserted into the drive, as if nothing was ever wrong.
I just C-A-A again.... booted fine.
Powered off....
Powered on....
Insert disk animation (normal boot).
Surely it's a voltage problem somewhere. I wonder if the magenta screen is actually the machine waiting for the voltages to settle down still.
I've just ordered some 22uF and 100uF Rubycon caps to replace the cheap ones I was using, maybe they'll help on the -12V and +12V lines. Maybe D175 could be changed too.
And just ordered some 10nF for good measure. Maybe they need replacing too.
I just power cycled again... back to black screen. Didn't touch anything, it just didn't reboot... but I reckon if I wait a while it may do!
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Sounds like it could be bad motherboard capacitors. Have they been changed? If they haven't, then remember they're 20 years old now. Just a thought.
Another thought would be the main oscillator on the motherboard (28MHz on A4000?). I've never had one die on me before, but it is possible. I know they can go flaky and sometimes die completely, so it's something else to consider.
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The electrolytics have all been changed. So far I've changed all of them once, and then I changed the 47uf (the ones on the +5V line) with low ESR Rubycon ones. I've got more Rubycons on the way for 22uF and 100uF.
The oscillator is fine, because once it starts working it continues to work fine - until I turn it off.
I think you're right, though, it must be the caps, surely.
Interestingly, the +12V_USER rail is at 11.65V - I wonder if that's enough.... the PSU is giving out +12.4V, but the other side of D175 is only 11.65V. Is that normal...?
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11.65V on the +12V line should be fine that within a 5% Tolerance. Are you measuring the power with the CSPPC and are any other cards installed?
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The electrolytics have all been changed. So far I've changed all of them once, and then I changed the 47uf (the ones on the +5V line) with low ESR Rubycon ones. I've got more Rubycons on the way for 22uF and 100uF.
The oscillator is fine, because once it starts working it continues to work fine - until I turn it off.
I think you're right, though, it must be the caps, surely.
Interestingly, the +12V_USER rail is at 11.65V - I wonder if that's enough.... the PSU is giving out +12.4V, but the other side of D175 is only 11.65V. Is that normal...?
I don't know what D175 is, but if there's no hard drives attached then I believe that the +/- 12V rails are used for the audio amplification circuit only, so I wouldn't count on the 12V line being important at this stage.
The oscillator is fine, because once it starts working it continues to work fine - until I turn it off.
If all else fails, and you've replaced all the caps, then you could try the oscillator as a last resort. Maybe sometimes it just doesn't start up correctly. Small chance, but you never know your luck. You could try reheating it before replacing it. A couple of months ago there was someone on here with a Blizzard1230IV which had a dry joint on its oscillator.
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I wish it were as simple as the oscillator! If that were the case though then the CS-PPC would still be working, as that uses the external clock.
D-175 is the diode seperating the PSU's +12V line and the usable +12V_USER line. It's got a voltage drop of about 0.7V which I think is correct.
I think again you're right about the +12V line being just for the audio amp, but I believe the Amiga checks for a steady +12V rail before booting doesn't it? This is the usual cause of A600s not booting, I believe. It certainly looks like this is what's happening, anyway...
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I wish it were as simple as the oscillator! If that were the case though then the CS-PPC would still be working, as that uses the external clock.
D-175 is the diode seperating the PSU's +12V line and the usable +12V_USER line. It's got a voltage drop of about 0.7V which I think is correct.
I think again you're right about the +12V line being just for the audio amp, but I believe the Amiga checks for a steady +12V rail before booting doesn't it? This is the usual cause of A600s not booting, I believe. It certainly looks like this is what's happening, anyway...
The 28MHz clock is required for the custom chips and video circuit. This is always in use whether you have an accellerator card or not. :)
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Just swapped it (the crystal) and it didn't improve. I had to swap it with a non-known-good one though (from a broken A600) so it's possible it's broken on both, but I doubt it. Going to fix the A600 and see if it works with the crystal to find out.
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Hi people,
Still fighting my A4000.
Occasionally it boots, and I'm fairly sure now it's to do with the CPU connector. I've got the voltages up nicely, so that should be ok.
I've cleaned and re-cleaned the CPU connector but it's so bloomin' difficult to get at, I still can't be sure it's clean.
Anyhoo, the symptom at the moment is a bright magenta screen on a cold boot. I know the CPU is basically working because if I remove the chip RAM, then it sure enough boots to a green screen.
Very occasionally I get a white screen.
Quite often I get nothing at all - just a dark grey screen as though the CPU is doing nothing.
I've tried with both the original 030 module and the CS-PPC, same thing on both.
All this time the Caps Lock light works as it should, no error codes or anything there.
Anyone got any ideas? Thanks if so!
Hi Ian,
Have you tried pulling & cleaning the ROMs, and checking for any broken legs? May also be worth checking the DIL socket solder joints to the motherboard also.
Purple Not an "official" color, but may be caused by
bad ROMs.
http://web.archive.org/web/20081018170130/http://home.nikocity.de/rs/A4k-HW3.html
also
http://www.amiga.org/forums/showthread.php?t=35177
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I just checked the ROMS - they contain the correct data, so that's ok.
I think I'll check the connections next.... I've already tried reseating them, they're both good.
One person in that thread said that he had a similar problem with leaking caps on the sound module - that'd imply a +/- 12V line error, though, which I do suspect....
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Well.. I found the cause of the mysterious magenta boot screen!
One time when my A4000 managed to boot, and it was sitting on the insert disk screen, the screen suddenly went magenta again.
But what was weird was that the screen then filled with white lines.... but I could see the insert disk screen in the background!
I quickly checked Alice's temperature, to see if it was hot, and... the lines disappeared!
Let go of the chip... lines return. Press on chip, lines go. Hah!
One quick reheat of the chip with the Aoyue SMT rework station, and the problem got worse - black screen with bad sync.
Not giving up, I took Alice off completely, put a bit of fresh solder on some of the pads, put Alice back on...
Bing! Machine boots! First time! And second time! And every time for the last 30 or so attempts.
So if your A4000 doesn't boot, and you get sporadic booting with no obvious symptoms, just maybe you just need to resolder a custom chip or two.
Hurrah! Now I think I'm going to find a heatsink for Alice.....
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Good job Spirantho. in all the A4000's i have had/worked on i have yet to have to resolder any custom chips due to bad contact. it was always something else.I guess you must of got a friday board(they were in a hurry to get to the bar after work) lol.
good job finding it. that was a tough one.
mech