Amiga500 rev 5 fails to boot, flickering powerled and screen

[Firestone]

Hi everyone!

First some background:
For a while this board (which was my first Amiga btw), have had a hard time booting if it hasn't been used for a few days.

The sympthoms were that when I powered it up, there would only be a black screen, and after a few minutes, the powerled came on and kickstart-screen was displayed.
I could trig this with resetting the machine, and everything would work normally. No instabilities, nothing, it would work just fine.

Lately after using it, I noticed some strange smell from the motherboard, and I think it comes from around the chipram in the lower left part of the motherboard.

Yesterday I decided to change capacitors to see if this would help on at least this weird bootproblem.
But now the machine won't boot at all.
I power on, and I hear the first click in the disk drive. Powerled is off. (you have to take into consideration that this is one of the machines with the red powerled with no half-bright state, read: off when audiofilter is off).

After a few seconds, there is some grey flickering on the screen and the 1084 makes some weird sounds (not from the speaker, but probably because it's recieving some strange signals and unable to sync).

Then the powerled starts flashing fast and at the same time the screen flickers.

Take a look at this video:
[ Show youtube player ]

I have tried changing the kickstart to DiagROM, but the same thing happens.
I noticed on a picture I took of the motherboard BEFORE I recapped it that C17 looks burned. Can this probably have something to do with it? :

[r.cade]

It looks burned so far it's disconnected. Likely there is too much current being pulled there. Could be failing RAM chip.

[Firestone]

Do you think the failing ramchip gives the problems as shown in the video?

[r.cade]

I don't know. When I've had just bad RAM, typically the screen instantly comes up green. So, probably there are other issues.

[Firestone]

This must be something else as I get no picture at all, just this wierd flickering simultaneously with the powerled

[Rotareneg]

That was a tantalum cap which are notorious for failing shorted, as seen by how it got hot enough to melt it's own lead. I'd check voltages first, it may have damaged the power supply or other components, or even burned a trace on the board.

[Firestone]

Checked the powersupply just now on my other A500 and A500+. Works fine there.
Have done som random measures around the motherboard. 12v and 5v seems stable.

The only suspicious thing I've seen so far is a possible broken trace on C324 negative side.
But isn' this only related to the audio-circuit? The board should still power on with faulty audio?

[Firestone]

Update:
After probing R503 I can see that the voltage fluctates in sync with the powerled. Besides this, it seems to stuck at around 5v (4,8 or so).

[kipper2k]

i would start off by removing U17 RAM chip, i notice that the batch number on that chip is different, unusual but maybe not an issue. Once ram removed try to boot and see what startup looks like, also if you have diagrom try booting from that

[solarmon]

Remove C17 and see what happens. It may have failed short. A single missing cap for the chip mem shouldn't stop it from booting (if that is th only issue)

[Firestone]

Originally Posted by solarmon

Remove C17 and see what happens. It may have failed short. A single missing cap for the chip mem shouldn't stop it from booting (if that is th only issue)

Thanks solarmon.... it actually did something. C17 came off in two pieces, and when I tried to boot, i saw the white screen that appears just before the kickstart-image, but then it returned to the same state again. Powerled was also stable when that happened.

[Firestone]

Originally Posted by kipper2k

i would start off by removing U17 RAM chip, i notice that the batch number on that chip is different, unusual but maybe not an issue. Once ram removed try to boot and see what startup looks like, also if you have diagrom try booting from that

Thanks for replying kipper2k!
I just tried to remove C17, read the post above. The U17 ram chip was I unable to remove right now because the iron decided to die on me

DiagROM-chip is now installed.
I have to add that I tested the machine with DiagROM BEFORE i recapped it, and it returned no errors with memory, the only thing I saw was a CIA timing failure with one of the tests.
This was even with a burned C17 installed.

[kipper2k]

you can remove even CIA and try rebooting, EvenCIA does not interfere with the bootup process, it will just prevent the floppy drive from booting...
also swap over CIA chip to see what happens then

[solarmon]

If it gets to the white screen, then I would suspect an issue with the interrupt signals - so with Paula and the traces and components associated with the interrupt signals.

This does not have it for a rev 5, which I need to add, but it might give you some hints as to where to check:

https://sites.google.com/one-n.co.uk...errupt-signals

I would reseat the socketed chips, cleaning the chip pins and sockets with isopropyl alcohol. Also, swap the CIA chips to see if it makes a difference.

[Firestone]

Update on this one!

It's alive again!:



There was broken connection between the negative side of C324 and C502.
The system boots just fine with kickstart 1.3 now.

But it won't boot with DiagROM anymore. Just a black screen, weird...

Just tested with Amiga Test Kit v1.5 and everything seems to work fine except from some CIA-timer errors:



CIAB TOD expect 5008 ticks: 912 -> FAIL

Is CIAB equalent to EVEN CIA?

A new symptom have occured twice after the machine has been powered on for a while. Screen flickers a little bit on the kickstart-image, and suddenly it gave me a Recoverable Alert......
System is completely stable when Amiga Test Kit is loaded, but on the kickstart-screen this strange thing happens.

I should mention that C17 is still missing. Can this be the reason? Memorytests never fail btw.

.......and now just as we speak I turned the system off. And now it won't boot again, but I see a white flickering screen this time.....aaoooffh!

[Firestone]

..... further investigation:

System boots fine as long as it has cooled down. Waiting for around 10 minutes or so, the system boots fine again.

Then after 2-3 minutes, the kickstartpicture starts shaking a little bit, then it gets worse and worse, and at the end there is only a flickering screen.

Swapped the CPU with another A500, but the same thing happens....
I have to say I'm really clueless on this one since it works at first, but after a while it does what I described above....

[Rotareneg]

Coolant spray (or upside down duster) would let you figure out which chip is heat sensitive if it isn't obviously overheating to the touch.

[Firestone]

Originally Posted by Rotareneg

Coolant spray (or upside down duster) would let you figure out which chip is heat sensitive if it isn't obviously overheating to the touch.

Actually I tried this yesterday, and when spraying the left side of the CPU it seemed to stable the system again.
For some really strange reason, I could play demos for a few hours and it worked perfectly!

For some reason now, the system seems to be stable, but today I suddenly got a NEW problem (wtf is this board cursed?).

Floppydrives won't read any disks. Both DF0 and DF1 are unable to read disks.

Symptoms now are:
Boots normal to kickstart-screen. As soon as we reach the kickstart screen and DF0 starts the normal clicking searching for a disk, the floppydrive led is ON!
For every click the floppy drive blinks and returns ON state again.
Inserting a disk activates the motor in the drive, but nothing is read.

Swapped the EVEN CIA with another A500, so I know it's good.
Is there any signals I can probe with a scope to troubleshoot this one?

Also tried several known good floppydrives of course.
..... and yes, the floppydrive is not reversed ...and I have tried multiple of them

[solarmon]

If you have a memory expansion - remove it. I've seen where a faulty memory chip can cause floppy drive issues.

Also, reseat and clean the pins and sockets of the Paula and Gary chip.

[Firestone]

Originally Posted by solarmon

If you have a memory expansion - remove it. I've seen where a faulty memory chip can cause floppy drive issues.

Also, reseat and clean the pins and sockets of the Paula and Gary chip.

No extra memory installed.
Tried to clean and scrub sockets for paula and gary with IPA, and also the chips. Still the same.

Behaviour is different using a Chinon-drive vs av Epson-drive for example.
With the Epson-drive (from another a500), disk led is not on until I insert a disk and it starts reading. What happens here is that it clicks normally when the kickstartscreen is on, and when I insert a disk I hear this well known "swallow disk"-sound, followed by a step and then the motor stops. Kickstartscreen is back.