(Yet another) A4000 green screen thread

UberFreak · 25 November 2009, 01:45

Hi

I received an A4000D from a business that used it for video mixing, the unit was always ON (for 10+ years!) and worked flawlessly.
About two years ago it died & since then was stored, until I got it.

The battery was leaking, but no damage was seen around it (lucky for me!).
90% of the SMD caps were leaking as well, no visible damage except yellowish green legs on the caps themselves.

Today I cleaned the board & replaced ALL capacitors, with through-hole type. Caps on CPU board (EC30@25Mhz) were replaced as well.

I tried to power-up the unit with nothing connected besides the CPU board (no daughter-board/fdd/hdd), all RAM sockets are populated.
Sockets + SIMMs visually inspected & cleaned.

On power-up, I immediately get a green screen, it very quickly flashes to black every second or so.
I've read numerous threads about this problem, the advice always has to do with the chip RAM, which I tried to replace.
I read on one of the threads about someone who also replaced the chip RAM socket but still got the green screen.

What else can this be?

I would really like to restore this unit to health (my very first A4000!) so any advice would be greatly appreciated

Thanks!

rkauer · 25 November 2009, 04:32

Did you clean the mobo in a dishwasher? Wait a pair of days after set it to dry in a vented cupboard well ventilated?

cosmicfrog · 25 November 2009, 13:10

chip ram is the first sim socket if i remember right

Jope · 25 November 2009, 13:16

Yep, closest to the daughterboard. Clean the contacts of the chip SIMM with isopropyl alcohol and a cotton bud or similar..

Just spraying it with something is not enough, you need a tiny bit of mechanical abrasion.

UberFreak · 25 November 2009, 15:58

As I mentioned in another thread, dont have a dishwasher

I cleaned the affected areas of the board with lemon juice & then alcohol, all traces of acid & corrosion were successfully removed.
There was no visible damage in the SIMM sockets area at all.

The chip-ram socket (and SIMM) were cleaned with alcohol, but I'll give it another round of cleaning (just in case) & report back.

cosmicfrog · 25 November 2009, 16:00

don`t forget to clean the sim as well

Good luck hope it comes to life

chiark · 25 November 2009, 16:11

If all traces of acid and corrosion have gone, the acid may have corroded a track which has now gone...

Check all the vias, traces etc near the battery/simm sockets. And good luck!

UberFreak · 25 November 2009, 17:34

Some possibly sad news...

Cleaning didnt help, but I performed the "touch test" with all ICs, and noticed the 8520PL gets very hot to the touch in a second or two, the other ICs remain quite cool.
I just returned from a friend who also has an A4000, the 8520PL on his board remains cool.

So it seems I have a bigger problem here

Can I assume the 8520PL is gone, or can something else cause it to heat up?

EDIT: (possibly) bad CIA is U300

UberFreak · 25 November 2009, 17:35

Forgot to mention, the other CIA chip is a 8520A, which remains cool.

Jope · 25 November 2009, 20:06

Swap it out and you'll see. :-)

UberFreak · 25 November 2009, 20:32

Sadly, thats not an option at the moment.
Dont have a spare CIA or the proper equipment to remove/replace it.

If I only disconnect it from the +5V feed, can the board boot without it?

rkauer · 26 November 2009, 02:19

Depends on what CIA is busted. One is responsible for part of floppy functions. So, without it, no bananas.

UberFreak · 26 November 2009, 10:24

It's the one that handles the serial port, according to schematics

Shadowfire · 26 November 2009, 21:41

It is very likely that the internal gate insulation on one of the input/output transistors has been destroyed. The transistor now conducts from the gate to the source or drain, forming an unintended internal path for current.

In layman's terms, the chip has probably been ruined, has an internal short, and needs to be replaced. It is uncertain that even removing the +5v from it will allow the machine to boot, because the input/output protection circuits on these IC's can allow the chip to draw power from ANY high level input line if the +5V is disconnected... which may blow other IC's connected to it.

I would suggest finding someone that can perform the surface mount replacement operation before spending any more time on this board. Having a short on the board is one issue that you can't just ignore, and may (indirectly) be the cause of the green screen (for instance, it might pull the +5V line low and the local ground high, which could affect operation of IC's near it on the PCB).

Remember electrostatic discharge (ESD) safetly rules when operating on electronic circuit boards. Also, when performing shotgun repairs like this (where you don't know for sure what the culprit is), don't immediately trash the IC, you may discover after slapping a new one in that the machine still has the same issue and that the problem was elsewhere.

Shadowfire · 26 November 2009, 21:51

Also, after reviewing the schematic, it is unlikely that the 8520's are directly responsible for the green-screen (it seems to be responsible for serial/parallel/floppy functions). Since the processor can execute kickstart code up to and including the memory test function, the 8520 isn't messing around with the address or data bus. So you'll probably still have a green screen after that repair.

Although I've never seen or worked on an A4000, the green screen issues have surfaced on these forums several times before and the issue was always either a bad CHIP RAM SIMM or SIMM socket.

prowler · 26 November 2009, 23:30

Here is a useful online guide to Amiga 4000 hardware:
http://www.wonkity.com/~wblock/a4000hard/main.html

UberFreak · 27 November 2009, 02:18

Thanx for the warning, now I wont try to disconnect the CIA's power.

I think I'll stop messing with this board for now, I can possibly source another one, but that one is in an even worse shape - it has been through several repairs already & suffered from both battery & capacitor leakage, also one of the SIMM sockets is damaged.

Despite all this, the owner claims it boots up, so at least I know I have a working starting point!
Not really looking forward to the cleaning->removing old caps->soldering new ones routine again, but thats life I guess

UberFreak · 28 November 2009, 17:31

Well, got me another board yesterday, which looked like a war-zone.
Worked on it all day today, cleaning, replacing caps, tiding up.
It looks much better now, and even boots fine from HDD

Still one thing left to do though, since two of the SIMM sockets are broken, the previous owner used hot-glue to keep the SIMMs in place...
Need to decide if I should keep it like this, or try to find a better solution.

As for the first board, I'll just keep it for spares, not much else I can do with it

25 November 2009, 01:45	#1
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	(Yet another) A4000 green screen thread Hi I received an A4000D from a business that used it for video mixing, the unit was always ON (for 10+ years!) and worked flawlessly. About two years ago it died & since then was stored, until I got it. The battery was leaking, but no damage was seen around it (lucky for me!). 90% of the SMD caps were leaking as well, no visible damage except yellowish green legs on the caps themselves. Today I cleaned the board & replaced ALL capacitors, with through-hole type. Caps on CPU board (EC30@25Mhz) were replaced as well. I tried to power-up the unit with nothing connected besides the CPU board (no daughter-board/fdd/hdd), all RAM sockets are populated. Sockets + SIMMs visually inspected & cleaned. On power-up, I immediately get a green screen, it very quickly flashes to black every second or so. I've read numerous threads about this problem, the advice always has to do with the chip RAM, which I tried to replace. I read on one of the threads about someone who also replaced the chip RAM socket but still got the green screen. What else can this be? I would really like to restore this unit to health (my very first A4000!) so any advice would be greatly appreciated Thanks!

25 November 2009, 17:34	#8
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	Some possibly sad news... Cleaning didnt help, but I performed the "touch test" with all ICs, and noticed the 8520PL gets very hot to the touch in a second or two, the other ICs remain quite cool. I just returned from a friend who also has an A4000, the 8520PL on his board remains cool. So it seems I have a bigger problem here Can I assume the 8520PL is gone, or can something else cause it to heat up? EDIT: (possibly) bad CIA is U300 Last edited by UberFreak; 25 November 2009 at 18:31.

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25 November 2009, 04:32	#2
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	Did you clean the mobo in a dishwasher? Wait a pair of days after set it to dry in a vented cupboard well ventilated?

25 November 2009, 13:10	#3
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	chip ram is the first sim socket if i remember right

25 November 2009, 13:16	#4
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	Yep, closest to the daughterboard. Clean the contacts of the chip SIMM with isopropyl alcohol and a cotton bud or similar.. Just spraying it with something is not enough, you need a tiny bit of mechanical abrasion.

25 November 2009, 15:58	#5
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	As I mentioned in another thread, dont have a dishwasher I cleaned the affected areas of the board with lemon juice & then alcohol, all traces of acid & corrosion were successfully removed. There was no visible damage in the SIMM sockets area at all. The chip-ram socket (and SIMM) were cleaned with alcohol, but I'll give it another round of cleaning (just in case) & report back.

25 November 2009, 16:00	#6
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	don`t forget to clean the sim as well Good luck hope it comes to life

25 November 2009, 16:11	#7
chiark Needs a life Join Date: Jan 2008 Location: England Posts: 1,707	If all traces of acid and corrosion have gone, the acid may have corroded a track which has now gone... Check all the vias, traces etc near the battery/simm sockets. And good luck!

25 November 2009, 17:35	#9
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	Forgot to mention, the other CIA chip is a 8520A, which remains cool.

25 November 2009, 20:06	#10
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	Swap it out and you'll see. :-)

25 November 2009, 20:32	#11
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	Sadly, thats not an option at the moment. Dont have a spare CIA or the proper equipment to remove/replace it. If I only disconnect it from the +5V feed, can the board boot without it?

26 November 2009, 02:19	#12
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	Depends on what CIA is busted. One is responsible for part of floppy functions. So, without it, no bananas.

26 November 2009, 10:24	#13
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	It's the one that handles the serial port, according to schematics

26 November 2009, 21:41	#14
Shadowfire Registered User Join Date: Aug 2001 Location: Connecticut USA Posts: 617	It is very likely that the internal gate insulation on one of the input/output transistors has been destroyed. The transistor now conducts from the gate to the source or drain, forming an unintended internal path for current. In layman's terms, the chip has probably been ruined, has an internal short, and needs to be replaced. It is uncertain that even removing the +5v from it will allow the machine to boot, because the input/output protection circuits on these IC's can allow the chip to draw power from ANY high level input line if the +5V is disconnected... which may blow other IC's connected to it. I would suggest finding someone that can perform the surface mount replacement operation before spending any more time on this board. Having a short on the board is one issue that you can't just ignore, and may (indirectly) be the cause of the green screen (for instance, it might pull the +5V line low and the local ground high, which could affect operation of IC's near it on the PCB). Remember electrostatic discharge (ESD) safetly rules when operating on electronic circuit boards. Also, when performing shotgun repairs like this (where you don't know for sure what the culprit is), don't immediately trash the IC, you may discover after slapping a new one in that the machine still has the same issue and that the problem was elsewhere.

26 November 2009, 21:51	#15
Shadowfire Registered User Join Date: Aug 2001 Location: Connecticut USA Posts: 617	Also, after reviewing the schematic, it is unlikely that the 8520's are directly responsible for the green-screen (it seems to be responsible for serial/parallel/floppy functions). Since the processor can execute kickstart code up to and including the memory test function, the 8520 isn't messing around with the address or data bus. So you'll probably still have a green screen after that repair. Although I've never seen or worked on an A4000, the green screen issues have surfaced on these forums several times before and the issue was always either a bad CHIP RAM SIMM or SIMM socket.

26 November 2009, 23:30	#16
prowler Global Moderator Join Date: Aug 2008 Location: Sidcup, England Posts: 10,300	Here is a useful online guide to Amiga 4000 hardware: http://www.wonkity.com/~wblock/a4000hard/main.html

27 November 2009, 02:18	#17
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	Thanx for the warning, now I wont try to disconnect the CIA's power. I think I'll stop messing with this board for now, I can possibly source another one, but that one is in an even worse shape - it has been through several repairs already & suffered from both battery & capacitor leakage, also one of the SIMM sockets is damaged. Despite all this, the owner claims it boots up, so at least I know I have a working starting point! Not really looking forward to the cleaning->removing old caps->soldering new ones routine again, but thats life I guess

28 November 2009, 17:31	#18
UberFreak Registered User Join Date: Sep 2009 Location: the world Posts: 439	Well, got me another board yesterday, which looked like a war-zone. Worked on it all day today, cleaning, replacing caps, tiding up. It looks much better now, and even boots fine from HDD Still one thing left to do though, since two of the SIMM sockets are broken, the previous owner used hot-glue to keep the SIMMs in place... Need to decide if I should keep it like this, or try to find a better solution. As for the first board, I'll just keep it for spares, not much else I can do with it

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