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AuthorTopic: Amiga 1200 freezing/crashing issue  (Read 806 times)

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Offline khiiri

Amiga 1200 freezing/crashing issue
« on: May 30, 2014, 07:58:25 AM »
I have a NOS Escom Amiga 1200. I bough it about a year ago. It was freezing and crashing soon after I put it into use, so I did recapping of the mobo. After this the system worked flawlessly for several months.

During the winter months I had to store the Amiga in a storage where temperatures matched the normal Finland winter outdoor temperatures -30 to +5 Celcius degrees. After putting the amiga back into use now in Spring, the freezing/crashing is back.

I already recapped again the 5V line 1000uf cap, because I suspected it had gone bad during winter. I've tested with three different power supplies, all of them stored in room temperature, no difference. One of the supplies is Amiga 500 PSU and two others Amiga 1200 PSUs.

The crashing is bad initially when turning on the power, it might be that the system won't boot at all before hitting keyboard reset multiple times or boots up to workbench but then after couple of seconds (or after longer while) the screen either flashes or goes black and mouse freezes. Keyboard reboot helps again.

After it does this about half an hour, power continuously on, the system becomes very stable. So it kind of needs warming up. But what can be wrong? Caps? But they were all changed a year ago and the 1000uF ones again last week. Could it be the small caps, 0.22uF etc. (are they tantalum or some such?)? I've only changed the recommended SMD and radial caps. I've checked the soldering on all caps, looks good. Mobo traces all look good.

EDIT: some more info. I've tried with various configurations: with/without CF IDE attached, with/without floppy drive attached, with/without ACA-1220 attached. I reseated kick roms several times. No change, symptoms are always the same. I've been measuring the 5V line with a multimeter just after the 1000uf cap, and it gives me steady 5.03V even when the freezing or crashing happens.

Also usually this crash makes whole screen to display mess (I use RGB Scart) and floppy drive ticking stops so I think the CPUs not running anymore. Could it be RAM issue as well?
« Last Edit: May 30, 2014, 10:18:56 AM by tiebp »
 

Offline khiiri

Re: Amiga 1200 freezing/crashing issue
« Reply #1 on: June 02, 2014, 11:00:54 AM »
Been wrestling with this over the weekend. I modified a power supply from 400W ATX power, but didn't help. It's clearly not weak power. And my Amiga 500 works just fine with all the power units, so...
 
 I tried to do some measurement with multimeter, didn't really find out anything other than that sometimes, when the amiga doesn't boot up at all, HALT signal seems to be low. It's first at 5V for about second when I power up, but then goes low. What could be doing this?
 
 Anyway if the HALT is low, and I cycle the power, the HALT stays high afterwards. But also in this case the amiga doesn't boot up every time. Not until I let it heat up 15-30 mins. And the screen is flickering sometimes, like there is some kind of signal in the RGB output. Also Caps Lock freezes after several presses, indicating the CPU is not running, right?
 
 Oh well, I ordered other Amiga 1200 from ebay, dirty and yellowed, missing some keys. But I'm only interested in the mobo inside the unit. In case I can't fix this one.
 

Offline Ral-Clan

Re: Amiga 1200 freezing/crashing issue
« Reply #2 on: June 02, 2014, 11:14:38 AM »
I've stored many Amigas, retro computers, old SCSI hard drives and other hardware out in my garage here in Canada (-30 to +5 C) during the winter.  Some have been out there for years and I've never had a hardware problem with any of them.

The fact that your Amiga behaves WORSE when first starting, and starts to behave better after having been on a while, would seem to indicate to me dried out capactors (i.e. slow to hold a charge).  I know you've had them all replaced, but perhaps one was missed or a bad/old capactor was used in the replacement?

I think a good start would be to replace ALL capactors that have not yet been replaced.
Music I've made using Amigas and other retro-instruments: http://theovoids.bandcamp.com
 

Offline danbeaver

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Re: Amiga 1200 freezing/crashing issue
« Reply #3 on: June 02, 2014, 12:14:24 PM »
A prior capacitor leak could have damaged a trace by dissolving the copper and could be your problem.  There are folks to fix those type issues.
 

Offline khiiri

Re: Amiga 1200 freezing/crashing issue
« Reply #4 on: June 02, 2014, 12:55:51 PM »
Yeah I agree the symptoms would indicate capacitor issue. Only capacitors I haven't changed yet are the very small ones, ceramic I believe they are. I'm sure I got all the radial and SMD changed. Maybe I should redo all again, but it sounds weird they go bad in less than a year. And as I said, I already changed the two 1000uf radial caps already few days ago, other one is related to power input filter, other one is for the composite video out. And composite video out is fine, when the device boots up.
 
 There was some leakage from the bad SMD capacitors on the pcb when I changed them. I tried to clean it well and checked the traces, but couldn't see any damage. Well I'll check again, but I've been staring the board several days now and visually it's in very good condition. Anyway, it was working well before I put it into storage for winter.
 

Offline danbeaver

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Re: Amiga 1200 freezing/crashing issue
« Reply #5 on: June 02, 2014, 02:05:46 PM »
As a 4-layer board, you may not see damaged traces, but have to refer to checking with a multimeter and the schematics.
 

Offline TCMSLP

Re: Amiga 1200 freezing/crashing issue
« Reply #6 on: June 02, 2014, 04:50:15 PM »
Quote from: danbeaver;765546
As a 4-layer board, you may not see damaged traces, but have to refer to checking with a multimeter and the schematics.


Have you checked/reseated all the socketed ICs?  Working when warm could also indicate a corroded pin/connection somewere making better contact when things have expanded.

I'm sure you've probably already tried that, but thought it worth mentioning anyway, just in case!


Steve
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Offline khiiri

Re: Amiga 1200 freezing/crashing issue
« Reply #7 on: June 02, 2014, 05:17:21 PM »
Yeah I have reseated the socketed ICs. There's only the Kickstart ROMs that are socketed on Amiga 1200 2B board. I reseated them many times, scratched all oxidation from the pins as well, no help.
 
 I don't know, I think I'm going to give up with this and wait for the replacement board. I think it would be easier to debug a fault which would make it to not work at all, rather than this kind of random issue. I don't have a scope either, just a multimeter.