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Old 19 January 2020, 19:56   #1
LeCoq
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Problems with an A500+

Hello!

I guess a little introduction is in order, before I get to my problem. This is pretty much a copy-paste of my message at Lemon Amiga, but I hope it doesn't matter. I asked there first, but thought it doesn't hurt to ask here too, since I don't know how connected the community is. Anyway...

It's the usual story. I used to own an Amiga 500 as a kid, back in the early nineties. Sold it later on as I moved on to a PC. Had regrets afterwards. Fast forward a decade and a friend's father, gave me three Amiga 500s for free that went into storage at my parents house. Few months ago from now (after almost 15 years since I got the machines), I had a rush of nostalgia and remembered I had the Amigas. I dug them out and powered them on. All of them booted up, but I had no peripherals or a monitor for them.

Long story short, I bought one more Amiga, that came with peripherals to use them. I now had four (more or less) working Rev.6A Amigas. I then bought an ACA500plus, and have been learning how to use the Workbench 3.1 and playing some WHDload games.

Then I got it in my head, that I had to have a 500 Plus in my collection. I bought one from eBay, that had it's battery removed. As soon as I got it, I inspected the damage, the leaking battery had done. I think it's not too bad. At least I've seen videos of way worse damage in working Amigas.



It works perfectly fine with just the ACA500plus, without a trapdoor memory expansion. It gets clean results in Amiga Test Kit memory tests, loads games etc. Everything works.

It's when I connect either of my two Zydec AmRAM-16 512KB memory expansions (tested to work on another Amiga), that the troubles begin. Here's what happens.

1. Boots to WB 3.1 just fine
2. Sometimes grabbing a window and moving it around, produces screen "shaking" and messy graphics. Sometimes just moving the mouse does this. One time the screen just kept on glitching on it's own.
3. SYSINFO works fine.
4. Tried to launch a WHDload game (Super Off Road). The intro flashes for a split second, and then crashes with a red screen.
5. Amiga Test Kit crashes immediately, with the following screen. It's always "Exception #04 at PC", but the other stuff changes.




Here's video of the screen glitching.



To recap, the Amiga does these crazy things ONLY, when the trapdoor memory expansion is connected. Also, it doesn't matter which position the dip switch is in on the expansion card. It behaves the same way and even shows 1.5MB of chip memory, whether it's on or off.

I just checked some connections on the motherboard for continuity. First, I tested the vias that looked corroded. They all checked out fine. Next up were the pins on the trapdoor expansion port, but I couldn't find any faults in them either. I have to say, that the Amiga PCB Explorer was a huge help in checking the pins!


Any ideas, where I should look into next?
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Old 19 January 2020, 21:09   #2
solarmon
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The image of the battery area shows some corrosion (dark green and black patches) on various traces.

Have these been cleaned up and inspected for trace damage? If not, then that is the first thing to do. I suggest watching the Youtube videos by GadgetUK164 about repairing an Amiga A500plus.
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Old 19 January 2020, 21:29   #3
LeCoq
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Yes, I checked the traces and they all seem to be fine. I have also cleaned the area with vinegar and IPA. I've watched GadgetUK's videos on the subject, and they're a great help indeed.
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Old 19 January 2020, 21:55   #4
solarmon
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Quote:
Originally Posted by LeCoq View Post
Yes, I checked the traces and they all seem to be fine. I have also cleaned the area with vinegar and IPA. I've watched GadgetUK's videos on the subject, and they're a great help indeed.
What do you mean by "they all seem to be fine"?

Have you scratched away at the corrosion and re-tinned them?

They may have continuity when measuring with a multimeter but they may be marginal and the signal degraded going across them.

If ATK is not loading properly, then maybe it is best to get a DiagROM to do a health check.
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Old 19 January 2020, 22:32   #5
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If I were you, I would do what Solarmon suggested.

Scratch back and re-tin all those traces that look black.

Also, it might be worthwhile looking at U12, might have to take it off as my board had serious corrosion (yours has nothing on my board) broken traces all under that chip.

Good luck
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Old 20 January 2020, 05:03   #6
TjLaZer
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Not sure if trying to use a regular A500 mem expantion would cause any issues vs a proper A500+ 1MB card. Did you clean the pin contacts where the card plugs in?
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Old 20 January 2020, 05:26   #7
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Have you tried the expansion without the aca500plus? Maybe those two do not get along.
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Old 20 January 2020, 08:21   #8
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My speculation is about the 16 chip RAM expansion, perhaps it is not fully compatible with the new Agnus. But it's just speculation, so unless it is trivially easy for you to test the machine with a 4 chip RAM board, then don't bother. :-)
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Old 20 January 2020, 08:54   #9
solarmon
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Have you tried the trapdoor memory expansions without the ACA500plus card?

It might be that there is some kind of incompatibility between them, so try it without the ACA500plus connected.
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Old 20 January 2020, 17:37   #10
LeCoq
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First of all, thanks for all the replies.

To answer some of your questions:

Quote:
Originally Posted by solarmon
What do you mean by "they all seem to be fine"?

Have you scratched away at the corrosion and re-tinned them?
I haven't scratched away the corrosion on the vias, and neither have I re-tinned them. I only tested the continuity on them with a multimeter. Sorry, I should have been more clear. I have cleaned the affected area, as thoroughly as I could. That's what I've been able to do so far, with my competence in electronics. I thought that, if the vias turn out to be the culprit, then I could repair them with soldering wires on the other side of the board. I'm afraid re-tinning those fine vias is out of my league. But if that's what it really takes, I think I'll have to look into it.

Quote:
Originally Posted by TjLaZer
Did you clean the pin contacts where the card plugs in?
Yes, the pin contacts have been cleaned, and they were pretty clean to begin with.

I did get a chance to test it without the ACA500plus today, as you suggested. I had to use Gotek, after I unplugged the ACA500plus, because I have no software on diskettes.

1. ACA500plus detached, AmRAM 512KB memory expansion attached.
2. Booted straight to ATK no problem.
3. Memory test gave the following error. I tried it a couple of times, and it was always the same. It always detected the expansion and showed it as chip ram. Is it normal that on the 500 Plus, the expansion memory goes straight into chip mem and not slow? Because, on my regular A500s it shows as slow mem, unless I plug in the ACA.
4. It didn't matter if the memory expansion switch was ON or OFF, the results were the same.



I then tried it with the Gotek and memory expansion detached, and ACA attached. ATK works fine, but in direct memory test, I get this warning.



I did the same with couple of regular A500s, and it shows the same warning. So that must be related to the ACA. I can't remember seeing that warning before, but now it's always there..
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Old 20 January 2020, 21:19   #11
solarmon
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I suggest the following test to rule a few things out:

Perform an ATK memory test on the A500plus without anything attached.

If this is clean then the onboard chip memory is OK, and there is something wrong with the traces to the memory expansion connector, since you mentioned that the Amram memory cards are working in your other A500's (I would run an ATK memory test on them in your other A500s too).

It still goes back to the suspect traces, the two closest to the battery hole is /CCK_A and /UDS which are signals going to the expansion port and thus the expansions cards.

The suspect traces need to be dealt with, otherwise they will always be suspect in that state/condition.

Last edited by solarmon; 21 January 2020 at 17:20.
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Old 20 January 2020, 21:30   #12
LeCoq
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Quote:
Originally Posted by solarmon View Post
I suggest the following test to rule a few things out:

Perform an ATK memory test on the A500plus without anything attached.

If this is clean then the onboard chip memory is OK, and there is something wrong with the traces to the memory expansion connector, since you mentioned that the Amram memory cards are working in your other A500's (I would run an ATK memory test on them in your other A500s too).

It still goes back to the suspect traces, the two closes to the battery hole is /CCK_A and /UDS which are signals going to the expansion port and thus the expansions cards.

The suspect traces need to be dealt with, otherwise they will always be suspect that that state/condition.

Ok, I will do that. Just one dumb question. Is the ATK memory test supposed to "get to an end", or does it just repeat the rounds infinitely? I've sat and watched it go up to about round 8 before.


Again, thanks for the help.
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Old 20 January 2020, 22:12   #13
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ATK memory test will go on forever. It is like that so that you can do a soak test. I normally let it run up to 100 rounds for a small soak test.
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Old 21 January 2020, 17:11   #14
LeCoq
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Both memory tests (Kickstart and Direct) came out clean on the 500+, with no attachments. I also tested the AmRAMs again, on a working 500 and they came out clean too. I guess I'll have to deal with those corroded traces before I do anything else with the 500+. Addition to that, I'm working with Jens S. on figuring out if my ACA has suffered, because I attached it to the suspicios 500+.
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Old 25 January 2020, 15:13   #15
LeCoq
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Seems like it was a compatibility issue after all. I had forgotten, that I had a third 512KB memory expansion in one of my Amigas. It's a Roctec RM550C-F and therefore, different from the two AmRAMs I tested on the 500+. I plugged in the Roctec and everything seems to be working fine.


That being said, I'll still have to attend to those corroded vias at some point.
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