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lunatico

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A friend of mine picked up a AES and send it over to me as it got some troubles.

This is a 5V console and I highly suspect it was connected to the wrong power supply but I cant see any trace broken or component on a bad shape.

The console boots up but its on a green screen but its garbled with squares and there is noise in the screen following a vertical pattern that goes from top to the bottom of the screen.

aes.jpg


I checked up and a green solid screen indicates a Palette RAM R/W error but if anything it resembles more a calendar freeze error from a MVS system.

I would highly appreciate any advice to keep troubleshooting the console.
 
I'm no expert but I have been working on a few of these lately, and I learned a few things...

1) That's definitely a 5V console (you can tell from the green component on the lower left, and lack of the coil the 9V uses), so you're probably right about wrong power supply. Which means something is very very dead (as evidenced by your photo).

2) I don't think that screen would constitute "solid green"; "solid green" is literally solid green. Garbage screen indicates something else, could be any number of things (bad 68K, bad Z80, bad custom (probably LSPC2)).

Is the console "clicking" at all? Turn up the volume and listen; if it is, that's the watchdog's "click of death" (google it) which is usually something failing super early (probably 68K or maybe D0/C1 customs). You can disable the watchdog by grounding it (check the neo dev wiki) to see if you can get more diagnostics out of it.

My suggestion is install the diagnostic BIOS and see what happens. You must run it with a cart in the slot. You should also verify all the traces between the BIOS and the 68K.
 
I'm no expert but I have been working on a few of these lately, and I learned a few things...

1) That's definitely a 5V console (you can tell from the green component on the lower left, and lack of the coil the 9V uses), so you're probably right about wrong power supply. Which means something is very very dead (as evidenced by your photo).

2) I don't think that screen would constitute "solid green"; "solid green" is literally solid green. Garbage screen indicates something else, could be any number of things (bad 68K, bad Z80, bad custom (probably LSPC2)).

Is the console "clicking" at all? Turn up the volume and listen; if it is, that's the watchdog's "click of death" (google it) which is usually something failing super early (probably 68K or maybe D0/C1 customs). You can disable the watchdog by grounding it (check the neo dev wiki) to see if you can get more diagnostics out of it.

My suggestion is install the diagnostic BIOS and see what happens. You must run it with a cart in the slot. You should also verify all the traces between the BIOS and the 68K.
Thanks! :D

Will do, as soon I get everything up I will post the results.
 
Well I checked the traces in between nothing wrong so far.

I just managed to install the test bios and this was the screen:

bios test.jpg


it seems the palette banks are out of order, I will replace from a another PCB I got laying around.

Any suggestions or/and leads ?
 
I'm no expert, but I'd start buzzing traces going from the palette RAM to the customs and such. I suppose it is possible that wrong PSU zapped them both, but it's also likely it's a bad trace. These boards are notorious for being poorly made and susceptible to corrosion.

I myself had one with a fun issue where the VRAM chips were alternating between good and bad, turns out there was a single trace from the LSPC2 that was corroded and causing intermittent errors. Cleared right up once I patched it.
 
Well I followed the traces from the CXK5864BSP and everything was in order.

After that I decided to replace both, after installing sockets and replicating the error I got last time I decided to change to the rams I got from another aes that have sound but no video at all.

Curiously enough it showed very unstable sync and what would appear to be the same palette ram error, in the possibility of the rams dying in the process of extracting em I decided to take the same rams from a spare mvs system and it showed the same behavior. Because of the sync issue this is the best pictures I could take , as the others were eligible in garble or scrolling:

b2.jpg
b1.jpg

Then decided to try it with the regular bios and I was greeted with this screens also the sync instability disappeared:

b3.jpgb4.jpg

So I got less garble than last time and a new solid green screen resembling a neo stuck on the watchdog or clock error. I did checked the sound and its not ticking so I don't think it may be a click of death. I would appreciate any recommendation or if anyone got any case similar to this one. I have the slight suspicion that more things than the palette ram are not in working order.
 
It's probably not watchdog because the diagnostic can't run at all if the watchdog is enabled. Unless you or the previous owner grounded it in an attempt to do diagnostics...

What I'd do is check and see which of the custom(s) are connected to the palette RAM (check neodev wiki), verify all traces are good. This post might be helpful, and I think there's a schematic on neodev shwoing palette RAM connects to the DAC... which might explain that problem? I am splitballing here.

Hope this helps!
 
The palette RAM does often go bad but when it does my experience is the error is at the end of the address space

If there are bad traces it can be in the middle of the address space depending which traces are broken, but it would be unusual to see the same trace broken on both RAMs (you are getting AAAA meaning both upper and lower RAMs are returning AA)

Also the data that is being read is not 0000 (no data) which is what you would expect to see if the traces are dead

Your error is in a random area of the space and across both chips - so it is very unlikely to be the RAMs themselves

Something on the bus is interfering or has died
 
I just got time and sat on the workbench.

After some reading the I figured that the data bus on the palette rams its something like this: CXK5864BSP ->LS245 ->LS273.

I replaced all the mentioned chips and still I got the same error. Checked continuity between them and all seems on order.

Is there something I am missing? how I could test the LSPC so I know the error does not comes from there?

Is there is any trace chart like the one xian xi mentioned on this post ?
 
I am pretty sure It's all on neodev wiki which I linked in a previous post.
 
Have you checked traces from the LSPC to the components?
 
Have you checked traces from the LSPC to the components?
Could you show me which pins on the LSPC I have to check on what components? on the schematic shows a neo-g0 which my board revision doesn't use and I cant use the one on the neo geo.com thread as it not matches my board revision as well.
 
I don’t own an AES but I’ve fixed quite a few MVS boards

You don’t need me to tell you which pins go where, look at the board, follow the traces to see where they go. If you want someone to fix it for you then that’s different but you will likely need to pay for that

Lines going to RAM ICs will usually always go to the same section of the next IC in the line - one side is address, the other is data

kazuo has also pointed out these details are available on the neogeodevwiki - even if it doesn’t match your exact board revision, the changes between revisions are not going to be that drastic
 
Ok noted, going to follow traces backwards from the ram and see witch ones lead to the lspc . In case my poor English conveyed any kind of attitude or bad manners its way past my head. I appreciate both of your inputs on this case which probably its the most complex repair job I tried so far.
 
No attitude or bad manners from my perspective! I think Xodara and I are just trying to point you to the resources (schematics!) on the neodev wiki which you can use to try and troubleshoot.

If you get stuck after looking at them and probing around, let us know what you've done and we'll see what we can do! Just bear in mind it's really hard for anyone who doesn't have the board in front of them to guide you to what is wrong unless it is an obvious or common problem (which doesn't seem to be the case here).

Good luck!
 
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