Display and floppy issue

Rebate · 17 November 2018, 14:47

Hi,
Since I was a kid, my amiga 500 has had a display issue. This issue can be seen on the snapshot that I took when I recently decided to boot it up after all these years.

Basically :
- the issue is happening from time to time
- the boot screen is messed up and some pixels are randomly displayed on the workbench image
- no disk can be read
- if the issue happens when playing a game, I get read/write errors.

I changed the PSU with no success.
I think that I will swap the Cia chips since the floppy is involved.

Have you ever seen this before?
Thanks
Kind regards

dlfrsilver · 17 November 2018, 16:46

mmhh.... check the kickstart rom pins for corrosion or bad contact ;

Changing the PSU is in itself useless if a recapping is not done. The A500 requires it as does the other models.

Stedy · 18 November 2018, 00:50

Hi,

You have a defective solder joint on one of the address lines to the DRAM. The regular pattern of the stippling indicates it is a higher bit. If the RAM can not be read from or written to reliably the Amiga will crash. The floppy drive is read and the data buffered by the RAM, which is defective, hence the issues you see.

I identified the problem as to create a graphics display, you read the framebuffer, which is part of the chip RAM. If there is a faulty data or address line you will see a regular pattern as shown in your screen shot. A defective data bit show up as more corrupted pixels, an address bit shows up as corruption at set distances apart.

Check the RAM devices in your A500, look for any dull colour solder joints, contamination or short circuits. You do not need to recap this yet.

Rebate · 18 November 2018, 08:39

Thanks a lot to both of you.
@dlfrsilver, I changed my psu with one from nowadays meanwell 50rt
@stedy, great diagnosis!
I will check for the solder join.
Unfortunately now when I start amiga, I get a black screen. No drive light or power light. Keyboard lock key is working. Only one first noise from the drive. Screen is going black since the amiga is in scart and the TV gets a signal.
I will clean the board and re-socket all the IC.
Thanks again.

nexus · 18 November 2018, 08:47

every amiga needs a recap time is up on those caps if they were never replaced
that includes PSU and the amiga
so since you need to open it anyways might as well take care of everything
that way when you have other issues you will know its not a power issue or bad flaky caps
always good to get that out of the way and rule out
just remember just cause it works doesnt mean caps arent bad and when 1 or more are then they put strain on other components shorting there life
if it were me i would do caps 1st then diagnose other issues
but yeah clean and redo bad looking dull solder joints etc<FLUX is your friend

demolition · 18 November 2018, 15:15

Quote:

Originally Posted by nexus

every amiga needs a recap time is up on those caps if they were never replaced

Since it is an A500, recapping isn't mandatory. It won't hurt to recap a 500 (if done right), but it is not the first place I would look for any problems. The first I would do, since all the large ICs are in sockets, is to pry them out a little bit and then push them back in fully to make sure they make contact. In regards to the PSU, a recap may be more important since bad caps will cause excessive noise on the rails.

If the machine has a RAM expansion with a battery on it, e.g. an A501, then that could also cause some damage.

Stedy · 19 November 2018, 21:55

Hi,

Links to a few faultfinding guide on my website, first the A500/A2000 troubleshooter:
http://www.ianstedman.co.uk/downloads/a5kts1.jpg
http://www.ianstedman.co.uk/downloads/a5kts2.gif

From the guides, for your initial issue of the screen breaking up, look at U2 Agnus, U4 denise and U2 socket. Demolition already mentioned this.

My A500 developed a similar fault (black screen), have not gotten around to fixing it yet, I have 3 others to use first!

I checked the capacitors, they all measured within expected capacitance and ESR values. Might be a winter project to fix this.

salteadorneo · 20 November 2018, 13:22

Check the capacitors. Look first at the two electrolytics in the upper left part of the motherboard.

lesta_smsc · 21 November 2018, 04:25

Never seen this on Amiga but such artefacts on PC or Xbox 360 usually pointed to cold solder joint under GPU and sometimes the RAM chips.

I guess looking you could boot up and leave it on for 5 mins and place finger on the various chips to see if they 'heat up' and whichever feels cold might be the defective chip. Or boot by applying pressure to the various socket chips and then RAM to see if you can get a change in display colour or even the odd boot.

I doubt the capacitor is at fault given the A500 seem to be rock solid. Mine survived being dropped despite it cracking the case and damaging floppy disk drive!

Rebate · 21 November 2018, 10:16

Thank you all for the great advice.
Regarding the main issue (black screen), I popped out all the IC and put them back.
No change.
I got a yellow screen then black again.
I let the amiga on for I while and checked the heat. Gary was dead cold.
After reboot, green screen.
I guess that it's Gary. I will try to change it from another A500.

Regarding the other issue (read/write error and scrambled screen), I did not see any odd looking solder or capacitor. I will post some photo soon.
Thanks again.

Rebate · 25 November 2018, 10:56

Hi,
I took the suspected Gary to another Amiga. It works fine.

Then, since I have a green screen. It could be Fat agnus or its socket. When I squeezed the socket, the amiga went back to normal. Another touch and I get the green screen avain.

I think that I should change the socket and maybe the fat agnus.

Any advice on that? Is any 84pins socket good or should I buy an amiga spare part?
Thanks

nexus · 25 November 2018, 12:17

you could also just solder straight to the board and not worry ever about sockets warping over time

Stedy · 27 November 2018, 00:24

Hi,

Good progress with the faultfinding. Take a look at pins 43-51 of the Agnus socket, they control the DRAM address. If my diagnosis was correct, they are a likely cause. Any 84 pin socket should do but double check the dimensions.

Did you try cleaning the socket pins with a fibreglass pencil?

Rebate · 08 December 2018, 12:01

Hi
I ordered a fat agnus socket on ebay and I replaced the existing one.
The Amiga restarted.I have to test it for a while in order to see if the fix is effective.
Even if it restarted well, I do have a new error. When I hard reboot it I get a guru meditation. If I give it 10 seconds off before restart. There is no guru meditation.
Any idea on this?
Thanks again for the great help for finding a solution to my amiga issues.

17 November 2018, 14:47	#1
Rebate Registered User Join Date: Nov 2018 Location: Paris France Posts: 19	Display and floppy issue Hi, Since I was a kid, my amiga 500 has had a display issue. This issue can be seen on the snapshot that I took when I recently decided to boot it up after all these years. Basically : - the issue is happening from time to time - the boot screen is messed up and some pixels are randomly displayed on the workbench image - no disk can be read - if the issue happens when playing a game, I get read/write errors. I changed the PSU with no success. I think that I will swap the Cia chips since the floppy is involved. Have you ever seen this before? Thanks Kind regards Attached Thumbnails

18 November 2018, 08:47	#5
nexus Registered User Join Date: Aug 2017 Location: USA Posts: 728	every amiga needs a recap time is up on those caps if they were never replaced that includes PSU and the amiga so since you need to open it anyways might as well take care of everything that way when you have other issues you will know its not a power issue or bad flaky caps always good to get that out of the way and rule out just remember just cause it works doesnt mean caps arent bad and when 1 or more are then they put strain on other components shorting there life if it were me i would do caps 1st then diagnose other issues but yeah clean and redo bad looking dull solder joints etc<FLUX is your friend Last edited by nexus; 18 November 2018 at 09:04.

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17 November 2018, 16:46	#2
dlfrsilver CaptainM68K-SPS France Join Date: Dec 2004 Location: Melun nearby Paris/France Age: 46 Posts: 10,412	mmhh.... check the kickstart rom pins for corrosion or bad contact ; Changing the PSU is in itself useless if a recapping is not done. The A500 requires it as does the other models.

18 November 2018, 00:50	#3
Stedy Registered User Join Date: Jan 2008 Location: United Kingdom Age: 46 Posts: 733	Hi, You have a defective solder joint on one of the address lines to the DRAM. The regular pattern of the stippling indicates it is a higher bit. If the RAM can not be read from or written to reliably the Amiga will crash. The floppy drive is read and the data buffered by the RAM, which is defective, hence the issues you see. I identified the problem as to create a graphics display, you read the framebuffer, which is part of the chip RAM. If there is a faulty data or address line you will see a regular pattern as shown in your screen shot. A defective data bit show up as more corrupted pixels, an address bit shows up as corruption at set distances apart. Check the RAM devices in your A500, look for any dull colour solder joints, contamination or short circuits. You do not need to recap this yet.

18 November 2018, 08:39	#4
Rebate Registered User Join Date: Nov 2018 Location: Paris France Posts: 19	Thanks a lot to both of you. @dlfrsilver, I changed my psu with one from nowadays meanwell 50rt @stedy, great diagnosis! I will check for the solder join. Unfortunately now when I start amiga, I get a black screen. No drive light or power light. Keyboard lock key is working. Only one first noise from the drive. Screen is going black since the amiga is in scart and the TV gets a signal. I will clean the board and re-socket all the IC. Thanks again.

19 November 2018, 21:55	#7
Stedy Registered User Join Date: Jan 2008 Location: United Kingdom Age: 46 Posts: 733	Hi, Links to a few faultfinding guide on my website, first the A500/A2000 troubleshooter: http://www.ianstedman.co.uk/downloads/a5kts1.jpg http://www.ianstedman.co.uk/downloads/a5kts2.gif From the guides, for your initial issue of the screen breaking up, look at U2 Agnus, U4 denise and U2 socket. Demolition already mentioned this. My A500 developed a similar fault (black screen), have not gotten around to fixing it yet, I have 3 others to use first! I checked the capacitors, they all measured within expected capacitance and ESR values. Might be a winter project to fix this.

20 November 2018, 13:22	#8
salteadorneo Registered User Join Date: Oct 2018 Location: malaga Posts: 47	Check the capacitors. Look first at the two electrolytics in the upper left part of the motherboard.

21 November 2018, 04:25	#9
lesta_smsc Registered User Join Date: Feb 2012 Location: United Kingdom Posts: 3,173	Never seen this on Amiga but such artefacts on PC or Xbox 360 usually pointed to cold solder joint under GPU and sometimes the RAM chips. I guess looking you could boot up and leave it on for 5 mins and place finger on the various chips to see if they 'heat up' and whichever feels cold might be the defective chip. Or boot by applying pressure to the various socket chips and then RAM to see if you can get a change in display colour or even the odd boot. I doubt the capacitor is at fault given the A500 seem to be rock solid. Mine survived being dropped despite it cracking the case and damaging floppy disk drive!

21 November 2018, 10:16	#10
Rebate Registered User Join Date: Nov 2018 Location: Paris France Posts: 19	Thank you all for the great advice. Regarding the main issue (black screen), I popped out all the IC and put them back. No change. I got a yellow screen then black again. I let the amiga on for I while and checked the heat. Gary was dead cold. After reboot, green screen. I guess that it's Gary. I will try to change it from another A500. Regarding the other issue (read/write error and scrambled screen), I did not see any odd looking solder or capacitor. I will post some photo soon. Thanks again.

25 November 2018, 10:56	#11
Rebate Registered User Join Date: Nov 2018 Location: Paris France Posts: 19	Hi, I took the suspected Gary to another Amiga. It works fine. Then, since I have a green screen. It could be Fat agnus or its socket. When I squeezed the socket, the amiga went back to normal. Another touch and I get the green screen avain. I think that I should change the socket and maybe the fat agnus. Any advice on that? Is any 84pins socket good or should I buy an amiga spare part? Thanks

25 November 2018, 12:17	#12
nexus Registered User Join Date: Aug 2017 Location: USA Posts: 728	you could also just solder straight to the board and not worry ever about sockets warping over time

27 November 2018, 00:24	#13
Stedy Registered User Join Date: Jan 2008 Location: United Kingdom Age: 46 Posts: 733	Hi, Good progress with the faultfinding. Take a look at pins 43-51 of the Agnus socket, they control the DRAM address. If my diagnosis was correct, they are a likely cause. Any 84 pin socket should do but double check the dimensions. Did you try cleaning the socket pins with a fibreglass pencil?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

08 December 2018, 12:01	#14
Rebate Registered User Join Date: Nov 2018 Location: Paris France Posts: 19	Hi I ordered a fat agnus socket on ebay and I replaced the existing one. The Amiga restarted.I have to test it for a while in order to see if the fix is effective. Even if it restarted well, I do have a new error. When I hard reboot it I get a guru meditation. If I give it 10 seconds off before restart. There is no guru meditation. Any idea on this? Thanks again for the great help for finding a solution to my amiga issues.