Please help me troubleshoot my A500

[spudje]

Recently I got an A500 rev5, kick 1.3 cheap. It looks pretty good, almost no yellowing and given the fact that the ACA500plus was about to be released when I saw it I was easily convinced buying it. It also came with an A501 512kB memory expansion. That had some minor battery damage which I removed (battery and damage).

It runs fine most of the time, however I encounter some issues from time to time. The only major issue I can reproduce is with the Budbrain Psychotic Megademo.

I got out my old floppies (I still have my very yellowed original rev 5 kick 1.2 A500 stored somewhere). I tested a random couple of disks, most ran fine, but I also had some issues. But these are some observations of faulty behaviour.

- Defender of the Crown: Runs fine without the A501
- Defender of the Crown: Runs fine with the A501, but gives a guru when ctrl-A-A rebooting.
Nothing I really mind though.

- Budbrain Psychtic Demo
The Original disks crash early on (no not the guru at the beginning of the demo ), so I created some new ones from TOSEC adfs. Still the demo keeps crashing. It's either during depacking the first movie part or during depacking the Kaos demo, ll on the first disk. In both cases you a quick rainbow flash (overscan area) an then a crash/guru.

I tried all following hardware options, all result in same behaviour.
- With the A501 memory expansion and without it.
- With an 8371 Agnus and with an 8372a Agnus
- Without an ACA500plus: i.e. using native MC68000
- With an ACA500plus using the MC68EC000-10 on the ACA500plus. I tried many combinations here
- With/without force PAL
- With/without 1MB chip hack
- With/without 7 MB fastRAM
- Kick 1.3 native, Kick 1.2 & 1.3 from ACA
- And maybe some other variations

As said no difference in bahaviour.

So I guess I can exclude the following being faulty:
- Memory expansion, or even if it is faulty, it's not causing the issue I'm facing, since it also occurs without the a501
- CPU
- Agnus

Since the crash happens during depacking, with my lack of in depth Amiga technical knowledge, I would assume that I can exclude Paula, Denise and the CIAs as well? That leaves the mainboard memory as main suspect. Is that a correct analysis? However I did test the (mainboard and expansion) memory successfully with systest disk https://github.com/keirf/Amiga-Stuff...master/systest

Any help is appreciated!

[ajk]

Are you certain the demo (or the version you have of it) does not have a bug? Have you tried running it with another Amiga, if you have one? I would not draw too many conclusions regarding hardware if only a single item of software is having problems.

[E-Penguin]

Does the disk image run in winuae? You could exclude a corruption there.

[spudje]

The adfs work in WinUAE, I'll test on a different A500.

Update, runs fine on a different A500 as well. I'll run a memory test on the faulty one. Or I'll simply build one working A500 from the two I have now (working mb from yellowed case into nice case).

[appiah4]

Might be that your salvaging of the A501 did not go as well as you thought it did?

[spudje]

Whether the a501 is faulty or not, is not the cause here, because symptoms are identical with or without it plugged in.

So I did more troubleshooting work.

Tested with other a500
So I tried the same Psychotic demo disks in my own original (much yellowed) a500 (rev5, kick 1.2). And guess what, it worked without a problem.

Memory tests
I extensively tested the memory of the faulty a500 with both Advanced Amiga Analyzer and SysTest. No errors were found.

Floppies vs slave

So, the psychotic demo crashes in the faulty a500 when run from floppies. When I have it setup with the ACA500plus and a classicWB Wb3.1 CF setup the psychotic demo slave works without any problem. Since WHDLoad uses the native chipset I still think the only hardware that could cause the problem is the (chip)ram, since I assume WHDLoad does do some memory remapping?

Hardware inspection
So, My hardware knowledge is limited to being able to identify components on the mainboard and just making some visual inspection. The mainboard looks fine, memory chips look OK (see image).

Things I noticed:

• A weird hack/mod around Denise, only found one other image on internet with a similar mod. Anyone knows what it does (see image)?
• Gary has a very faded label, all other ICs have very readable labels (see image). Maybe it has been replaced? What does Gary do actually and could it be the cause of my issues?
• I guess the agnus slot pins need some more cleaning (see image)?
• Radiation shield is a bit wobbly. Should I try without?

In the end I might swap mainboards, my working original into the nice looking case of the faulty one. But still I would love to get this one working OK too.

[appiah4]

Gary controls the floppy among other aux and might be a culprit.

[bebek]

Have you tried new board with 1.2 kick?

[spudje]

Haven't tried with the 1.2 physical kick in this machine. May try doing that. In the meain time I tried some popular other demos:

- Rink a Dink - Redux: works (awesome demo!!)
- Hardwired: works
- State Of The Art: crashes in the beginning after the nice credits screen with the small icons and artist names
- Desert Dream: crashes after screen "PD Note", during/after what looks like depacking/decrunching.
- Arte: works

So, that seems to be the theme here, a crash during depacking...

[Shadowfire]

You appear to be having a memory corruption problem.
Possible culprits (in order of likelihood)
1. Low voltage on the 5V rail (check from GND to VCC at memory IC's, shouldn't be below 4.75V).
2. Agnus socket oxidized (the real fix is replacement.. you can try spray electronic cleaner as a first test)
3. Physically damaged bypass capacitors on the motherboard near the memory IC's / Agnus, or old electrolytic filter caps on the 5V rail (C811-C815) (these should be replaced if they are below 80% of their labelled value, which involves removing them from the motherboard).
4. Chip memory bad

[spudje]

Thanks shadowfire, that to me seemed the most logical indication as well. Thanks for giving me actual pointers how to nail it down!