English Amiga Board


Go Back   English Amiga Board > Support > support.Hardware

 
 
Thread Tools
Old 17 November 2018, 15:47   #1
Rebate
Registered User

 
Join Date: Nov 2018
Location: Paris France
Posts: 5
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
Click image for larger version

Name:	uq477yc9jv20lxo61limiyz8o3sacefw.jpg
Views:	111
Size:	936.6 KB
ID:	60861  
Rebate is offline  
Old 17 November 2018, 17:46   #2
dlfrsilver
CaptainM68K-SPS France
dlfrsilver's Avatar
 
Join Date: Dec 2004
Location: Melun nearby Paris/France
Age: 41
Posts: 7,855
Send a message via MSN to dlfrsilver
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.
dlfrsilver is offline  
Old 18 November 2018, 01:50   #3
Stedy
Registered User

Stedy's Avatar
 
Join Date: Jan 2008
Location: United Kingdom
Age: 41
Posts: 623
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.
Stedy is offline  
Old 18 November 2018, 09:39   #4
Rebate
Registered User

 
Join Date: Nov 2018
Location: Paris France
Posts: 5
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.
Rebate is offline  
Old 18 November 2018, 09:47   #5
nexus
Senior Member

 
Join Date: Aug 2017
Location: USA
Posts: 670
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 10:04.
nexus is offline  
Old 18 November 2018, 16:15   #6
demolition
Unregistered User
demolition's Avatar
 
Join Date: Sep 2012
Location: Copenhagen / DK
Age: 38
Posts: 3,770
Quote:
Originally Posted by nexus View Post
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.
demolition is offline  
Old 19 November 2018, 22:55   #7
Stedy
Registered User

Stedy's Avatar
 
Join Date: Jan 2008
Location: United Kingdom
Age: 41
Posts: 623
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.
Stedy is offline  
Old 20 November 2018, 14:22   #8
salteadorneo
Registered User

 
Join Date: Oct 2018
Location: malaga
Posts: 10
Check the capacitors. Look first at the two electrolytics in the upper left part of the motherboard.
salteadorneo is offline  
Old 21 November 2018, 05:25   #9
lesta_smsc
Registered User

lesta_smsc's Avatar
 
Join Date: Feb 2012
Location: United Kingdom
Posts: 1,362
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!
lesta_smsc is offline  
Old 21 November 2018, 11:16   #10
Rebate
Registered User

 
Join Date: Nov 2018
Location: Paris France
Posts: 5
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 is offline  
Old 25 November 2018, 11:56   #11
Rebate
Registered User

 
Join Date: Nov 2018
Location: Paris France
Posts: 5
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
Rebate is offline  
Old 25 November 2018, 13:17   #12
nexus
Senior Member

 
Join Date: Aug 2017
Location: USA
Posts: 670
you could also just solder straight to the board and not worry ever about sockets warping over time
nexus is offline  
Old 27 November 2018, 01:24   #13
Stedy
Registered User

Stedy's Avatar
 
Join Date: Jan 2008
Location: United Kingdom
Age: 41
Posts: 623
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?
Stedy is offline  
Old 08 December 2018, 13:01   #14
Rebate
Registered User

 
Join Date: Nov 2018
Location: Paris France
Posts: 5
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.
Rebate is offline  
 


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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Indivision AGA MK2 A4000D Display Issue mikem support.Hardware 10 07 May 2016 11:07
Automatic window resizing and track display issue mark_k support.WinUAE 8 27 December 2012 19:44
Strange A1200 display issue tetsu0san support.Hardware 15 30 October 2012 17:26
display issue (real amiga) DaveMB support.WinUAE 5 29 August 2011 03:09
VooDoo Display issue Daddy43 Hardware mods 3 20 July 2009 22:31

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 16:54.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Page generated in 0.07909 seconds with 14 queries