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Old 05 July 2018, 22:27   #1
crashserious
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A600 With Garbled Screen

Good day everyone,


I'm thinking I know the answer, but looking for second opinions. I purchased a A600 a week ago and the seller showed images of it working with the security seals in tact. (Lets assume for discussion purposes it was actually working and the screenshots weren't fabrications, mostly because there's no way to prove it)

When I recieved it, there was some garbage on the KickStart screen. I thought it might be my GBS-8220 Setup (It's a PAL system) or I didn't have it connected completely. So I toggled the Amiga's power and it got worse. See below.


http://pasteall.org/pic/show.php?id=...f0468e184c45a5


I'm no stranger to electronics repair. My question is-- could this be bad caps? And is it possible that they went this bad that quickly? Could pressure changes in the cargo hold of a plane across the Atlantic cause this?

Last edited by crashserious; 05 July 2018 at 23:53. Reason: fix typo
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Old 05 July 2018, 23:40   #2
Daedalus
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It's unlikely to be pressure related - cargo holds are normally pressurised with the rest of the cabin, and cargo aircraft are fully pressurised too. It doesn't look like the typical capacitor damage, that usually leaves the video with analogue-type issues, whereas that looks more like a bus or Denise issue. Does it still seem to be trying to boot? Can you hear the floppy clicking, waiting for a disk? I guess it's possible it has been dropped or kicked around in transit, and has damaged connections inside as a result.

Having said that, I can't rule out damage due to leaking capacitors either. If the seal is still intact, chances are they're already leaking. And yes, capacitors can suddenly let go - or rather, they can decay slowly for years while in storage without use, then on their first use they work, but their performance very quickly drops away after that, reflecting the years of decay.

Is the power supply known good?
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Old 05 July 2018, 23:51   #3
TjLaZer
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caps leak and cause damage to all Amiga's that use SMD caps.
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Old 06 July 2018, 00:53   #4
crashserious
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Yes, the Power supply is known good. It's from my A500 and works just fine.


As for dropped and kicked, it's possible but it really was packed VERY well by the seller. I buy and sell stuff all the time, and this was better than I normally package stuff. Impressive.


It does appear to be trying to boot. I will grab a floppy and see if it boots in a bit, but it's teh stereo typical floppy sense sound that's going on.

Update:

It does boot just fine. The really odd thing is that it appears to JUST be RGB output that is garbled. The composite output works just fine. I tried it on a whim and my TV actually displays PAL frequencies just fine. So It's JUST the RGB output that seems to be affected.


Quote:
Originally Posted by Daedalus View Post
It's unlikely to be pressure related - cargo holds are normally pressurised with the rest of the cabin, and cargo aircraft are fully pressurised too. It doesn't look like the typical capacitor damage, that usually leaves the video with analogue-type issues, whereas that looks more like a bus or Denise issue. Does it still seem to be trying to boot? Can you hear the floppy clicking, waiting for a disk? I guess it's possible it has been dropped or kicked around in transit, and has damaged connections inside as a result.

Having said that, I can't rule out damage due to leaking capacitors either. If the seal is still intact, chances are they're already leaking. And yes, capacitors can suddenly let go - or rather, they can decay slowly for years while in storage without use, then on their first use they work, but their performance very quickly drops away after that, reflecting the years of decay.

Is the power supply known good?

Last edited by crashserious; 06 July 2018 at 02:20.
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Old 06 July 2018, 11:38   #5
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Quote:
Originally Posted by crashserious View Post
It does boot just fine. The really odd thing is that it appears to JUST be RGB output that is garbled. The composite output works just fine. I tried it on a whim and my TV actually displays PAL frequencies just fine. So It's JUST the RGB output that seems to be affected.
Really? That's good news then. It's unusual for RGB faults to produce output like that in the analogue stages. I would suspect the video encoder chip is damaged in that case. Fortunately that can be repaired, though I'm still concerned that this is the work of leaking capacitors around that area. Best to get it looked at as soon as possible. If you're comfortable yourself, it might be worth opening it up and having a look at the condition of the board to the left of the IDE port. Be careful opening the case as the keyboard LEDS are on a short cable at the front and are easily damaged by pulling the case up, and the clips at the back are notoriously fragile.
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Old 06 July 2018, 14:42   #6
crashserious
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I agree, it is good news. Since it "works" I went ahead and opened it up. It was sold as sealed, and if it was complete junk, I didn't want to destroy that.


The board actually looks very clean and shiny. (June Bug Rev 2D) I don't see any signs of corrosion (dull gray solder joints) or leakage around the caps (discoloration). They aren't bulging at the tops or leaning to the side either. I'll have to get a closer look at it a bit later, possibly take a look at the signals with my Rigol 1054Z. I'm just unfamiliar with these boards, so I'm going to need to read up a bit.





Quote:
Originally Posted by Daedalus View Post
Really? That's good news then. It's unusual for RGB faults to produce output like that in the analogue stages. I would suspect the video encoder chip is damaged in that case. Fortunately that can be repaired, though I'm still concerned that this is the work of leaking capacitors around that area. Best to get it looked at as soon as possible. If you're comfortable yourself, it might be worth opening it up and having a look at the condition of the board to the left of the IDE port. Be careful opening the case as the keyboard LEDS are on a short cable at the front and are easily damaged by pulling the case up, and the clips at the back are notoriously fragile.
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Old 08 July 2018, 20:01   #7
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Even when the caps are looking good just repalace it.
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Old 09 July 2018, 02:42   #8
crashserious
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Yeah, I'm aware. I've got a degree in electronics, so I know "looks good" doesn't mean "not bad". I simply meant that they don't appear to have leaked... yet.


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Even when the caps are looking good just repalace it.
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Old 11 July 2018, 05:28   #9
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I may have found the culprit, but haven't had a chance to test yet.



It seems the GBS-8200 device I am using has a propensity to not function properly with a PAL (50Hz) input signal. This explains why the Composite works with a HD TV that will tune 576p PAL Composite signals, but teh RGB output doesn't work (The RGB Output is teh same signal that feeds the Composite output chip, according to teh A600 schematics, which is why I was so perplexed.)


I plan to implement a bypass of the onboard processor as I have seen done on a few articles talking about this problem. I'll post back with results.
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