AES 3-4 board repair

[brian.illsley]

Hi guys, a few years back I bought a AES second hand at a Bootsale(uk flea market). When I got it home, hooked it up there was nothing no power just a clicking and a flash on screen. so i opened it up , I was not prepaired for the mess that was to confront me. The previous owner had decided to try and socket the bios but in the attempt made a shocking mess of the board. I have cleaned it up and repaired all the traces I could find


first attempt was like this but sadly didnt work, but i used this image to help me track the traces.



Second attempt below still didnt help but was more tidy.



So after I had done this trace fix, all continuity from the bios chip to every point on the below diagram are connected and have no shorts



So still after all this im still getting the watchdog clicking which i assume is the machine waiting for the bios to kick in.

Im now stuck as i dont know where to go from here. Any help would be much appriciated.

 

[venchia3]

Mate, no idea how to help honestly but just wanted to drop a quick message saying you did a fairly impressive job in repairing all those broken traces.

Hope you can sort this out soon, fingers crossed

 

[Neo Alec]

You're on the right track. If it's the bios, that bios pinout image is what will get you there. You've checked for continuity, but have you checked that no connections are touching each other where they shouldn't? Check the pin neighbors 2-by-2.

Make sure these little ones under the chip I had to patch are connected. These are the easiest to burn up in my experience:



Are you sure the bios chip is good?

 

[brian.illsley]

You're on the right track. If it's the bios, that bios pinout image is what will get you there. You've checked for continuity, but have you checked that no connections are touching each other where they shouldn't? Check the pin neighbors 2-by-2.

Make sure these little ones under the chip I had to patch are connected. These are the easiest to burn up in my experience:

View attachment 63317

Are you sure the bios chip is good?

Thanks so much for the help, I have checked the bios pins for adjacent shorts and all are good. One thing I have noticed is that there is a very quick beep when I check for shorts across 5v and ground. but if I stay on the points it stops. Is that normal? I have check the points you suggested all are good. The thing is im also not convinced I have a good bois, I bunt my own and have no way of testing the eeprom.

 

[Neo Alec]

Yeah, the best way to know if the socket is good is to remove the stock bios carefully and use that to test the socket first because it's known to be working. Sounds like you don't have the original bios though.

 

[BIG BEAR]

Make sure the bios pins next to each other are not sharing continuity with ground and +5 being the exception of course.
BB

 

[maki]

maybe this can help:

on the right is the BIOS IC (27C1024) pinout, on the left the 68k, this way you can test the traces from the top
be aware that on the left counting starts with 1, while on the right it starts with 0, so Pin 29 on the left is A1 which should be connected to Pin 21 on the right, A0

however, lots of these traces also run to other ICs, can be checked next

can you take a pic of the screen when booting and share it here?
expectation is to see the "scrambled" screen when it can't boot at all, often caused by the BIOS that ain't 100% connected, can you hear/see the "click of death"?

 

[brian.illsley]

Hi all, Thanks for the replies. I unfortunatly dont have a lot of time during the week, so I'm sorry that can mostly reply mostly at weekends. I have tested Bios connections to the 68000 as requested above and all is connected. I have also tested to adjacent pins to check for shorts also all fine. I have tested all pins continuity with ground and all is as it should be. As far as I can tell all connections are good. I have ordered a known good original Japenese Bios from a reputable source (seen it working) and will try that. I'm also going to buy a new multimeter as I'm now having doubts with my tools (I neeed a new one anyway)

video of the "click of death"

Thanks to everyone

 

[Xian Xi]

Check the address lines from the WRAM and 68k, all address lines should be shared between both WRAM but data lines are divided by each bank of 8 bits to the 68k meaning lower RAM will be D0-D7 and upper will be D8-D15. Also depending on what size chip was used for the bios (bigger than a 1024) you may need to bridge pins 38, 39 and 40 so 5v is going to all 3 pins, if the EPROM used was bigger than a 1024 and it wasn't filled up then it would leave it in a float state. Having the 3 lines tied to 5v would select the first image on the EPROM.

 

[brian.illsley]

Hi all, I have once again checked all the connections from the bios to the diagarms above and all are connected. I know im missing somthing somwhere im just not finding it. I have now got a original Neogeo bios (are the jap and pal ones interchangable?) and have the same issues so hopefully know its not a fault with the Bios. I have checked the WRAM as discribed above and all seems to be connected fine. im slowly running out of options and really dont want to give up on this board.

Again thanks for all the help so far

 

[wesprice]

i'd put my $2 on it being one of the bios traces though given the earlier pictures. since you said you already checked for continuity as mentioned above by bigbear and neoalec check the bios for shorted lines, with the meter on continuity and put the probe on the first pin and check it against all the others for any shorts, move to the next pin and repeat until you have checked all pins... the traces under the bios run very close together and ive seen it before when somebody has tried to patch broken traces on a failed bios install that some of the solder mask got removed and the smallest amount of solder can join two lines together which will cause the above issue.

if you have no shorted bios pins and already have the hardware capable of burning eproms then you could burn the neogeo diagnostic bios..

Neo Diagnostics homepage

this will help you isolate further as providing your traces are ok it will boot without a cart and allow you to run further tests.

If it is still in the watchdog loop with the diag bios then the 68k can't boot there could be some instability in the power supply section to the 68k, an oscilloscope on the 5v pin of the 68000 should show any excess ripple, but 95% sure its a problem with the bios connection to the rest of the system

or if you really are SOL then the 68k could be dead, only seen that when somebody has shorted it out or used a wrong power supply... hopefully you find a shorted bios trace.. the 68k can be diagnosed if you have logic probe/oscilloscope (best) but verify the other stuff first.

 

[Neo Alec]

Remember, the bios pins have to be connected to ALL points in the list. Just because a pin connects to one doesn't mean it's connected to the other.

 

[brian.illsley]

i'd put my $2 on it being one of the bios traces though given the earlier pictures. since you said you already checked for continuity as mentioned above by bigbear and neoalec check the bios for shorted lines, with the meter on continuity and put the probe on the first pin and check it against all the others for any shorts, move to the next pin and repeat until you have checked all pins... the traces under the bios run very close together and ive seen it before when somebody has tried to patch broken traces on a failed bios install that some of the solder mask got removed and the smallest amount of solder can join two lines together which will cause the above issue.

if you have no shorted bios pins and already have the hardware capable of burning eproms then you could burn the neogeo diagnostic bios..

Neo Diagnostics homepage

this will help you isolate further as providing your traces are ok it will boot without a cart and allow you to run further tests.

If it is still in the watchdog loop with the diag bios then the 68k can't boot there could be some instability in the power supply section to the 68k, an oscilloscope on the 5v pin of the 68000 should show any excess ripple, but 95% sure its a problem with the bios connection to the rest of the system

or if you really are SOL then the 68k could be dead, only seen that when somebody has shorted it out or used a wrong power supply... hopefully you find a shorted bios trace.. the 68k can be diagnosed if you have logic probe/oscilloscope (best) but verify the other stuff first.

Again thanks you for your reply, and sorry for my lateness on getting back to you. I have yet again check all pins for connectivity and shorts to adjacent pins and all check out. I have even taken this board to work, we have a electronics department that have also check out the connections and they too have concluded that all pins across all chips are connected. I have voltage going to all the chips including the 68k but i dont have a oscillascope for further probing. I have burned a diag bios and I get the same thing, watchdog click.

If there is any further things I could check I would be or if anyone was willing to talk me through it and maybe even voice chat with me that would be awesome. Thanks everyone for all the help so far, I really appriciate the help. but I dont want to give up on this.