Closed A500+ Mainboard Fault Find / Repair

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WonkeyDonkey

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Well this is a bit of a strange situation. I have a 500+ board (Rev 8A or 8A.1). It currently has a double rom switcher (1.3 + 3.1), 1 Mb trapdoor ram expansion, indivision ecs. The board has been recapped and had some sockets replaced too as well as the battery, and plugged to a GVP A530. Great condition overall.

Now there seems to be a fault which I cant pin down :( When I power it up with the A530 and everything else connected, it goes into guru mode a few seconds after boot and then reboots. This cycle repeats while ever it is switched on.

Ive done the obvious which is to strip it down of all the added extras and it still happens. I get the feeling there is a short somewhere; maybe a track or two. Visually I cant see anything wrong at all, the recap work looks perfect and the sockets too.

When I plug all the extra bits into another 500+ I have, they all work fine, so its not a timing issue or anything like that. Im almost 100% sure the fault lies with the board but no idea what is causing this.

What Im after then is someone who can test all aspects of the board so I can get a repair sorted out and get her back on her feet once again.

Any experts willing to give this a go for a suitable fee ?

:coffee:
 
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Well this is a bit of a strange situation. I have a 500+ board (Rev 8A or 8A.1). It currently has a double rom switcher (1.3 + 3.1), 1 Mb trapdoor ram expansion, indivision ecs. The board has been recapped and had some sockets replaced too as well as the battery, and plugged to a GVP A530. Great condition overall.

Now there seems to be a fault which I cant pin down :( When I power it up with the A530 and everything else connected, it goes into guru mode a few seconds after boot and then reboots. This cycle repeats while ever it is switched on.

Ive done the obvious which is to strip it down of all the added extras and it still happens. I get the feeling there is a short somewhere; maybe a track or two as part of the recap that was done on it. Visually I cant see anything wrong at all.

When I plug all the extra bits into another 500+ I have, they all work fine, so its not a timing issue or anything like that. Im almost 100% sure the fault lies with the board but no idea what is causing this.

What Im after then is someone who can test all aspects of the board so I can get a repair sorted out and get her back on her feet once again.

Any experts willing to give this a go for a suitable fee ?

:coffee:


Hi,

The first place to start is to switch out all the socketed chips one at a time with substitute known good chips. Remove all addons... including the keyboard, floppy drive and internal/external ram etc. I have lots of spare chips so i can test this. The 555 timer portion of the motherboard controls the reboot function of this motherboard so that would be the area to start with first. You never mentioned, did the board actually suffer a battery leak at one time regardless how minor?.

Also, after the last repair when sockets and caps were added/changed, did the board work and then die at a later stage ? or was the repair unsuccessful. Knowing the history helps with the troubleshooting
 
It did suffer a very minor battery leak but did not reach a single track and was cleaned up immediately I received it. At that point and prior to the board being capped etc, it worked 100%.

---------- Post added at 00:43 ---------- Previous post was at 00:41 ----------

I have a set of chips I can trying swapping out from my other 500+ board, minus the Denise which I managed to bend all the legs over when swapping the indy.
 
It did suffer a very minor battery leak but did not reach a single track and was cleaned up immediately I received it. At that point and prior to the board being capped etc, it worked 100%.

---------- Post added at 00:43 ---------- Previous post was at 00:41 ----------

I have a set of chips I can trying swapping out from my other 500+ board, minus the Denise which I managed to bend all the legs over when swapping the indy.


Don't throw out the Denise, legs can be regrown :)
 
Well theyre not snapped (Yet!), just twisted round. Im not so concerned about that board though.

The one in question is the board which has had all the work done on it to get it into tip top condition and is my best board. I cant see this one fail on me now :(

Pics and further detail available here :

https://www.amibay.com/showthread.php?t=34518
 
Well theyre not snapped (Yet!), just twisted round. Im not so concerned about that board though.

The one in question is the board which has had all the work done on it to get it into tip top condition and is my best board. I cant see this one fail on me now :(

Pics and further detail available here :

https://www.amibay.com/showthread.php?t=34518

If you have given up trying to fix it and want me to look at it then i can. You just need to pay shipping costs, if i can't fix it then you pay nothing except for your shipping costs here and back. If i can fix it, then you pay me $20 (plus price of parts if needed).

Let me know

Regards

Brian
 
I checked your capacitor replacement list and i dont see the 2 x 3300uf capacitors on that list (these are the 2 located behind the video hybrid module) ?

All the A500+ boards i have seen have these fitted ? I don't think it would cause the reboots but all schematics i see show them at that value
 
That list came from the service manual and matched what was there IIRC.

:blink:

I think the 3300 uf are on the 500 boards at C401, C402.

On the 500+ board these are 1000 uf ?
 
That list came from the service manual and matched what was there IIRC.

:blink:

I think the 3300 uf are on the 500 boards at C401, C402.

On the 500+ board these are 1000 uf ?


Hi, You're right, i just rechecked the actual boards :)


Phew!

That would have been disaster if they had been done wrong :wooha:

Onto voltage testing and swapping chips as advised in PM next. Its a possibility for sure since the PSU is the only thing not tested so far.
 
Well the voltages at the floppy header check out ok. 5.09 and 12.19. Is there anywhere else i should be checking voltage measurements ?
 
Does it work without expansions connected?

Can you try without Indi, additional 1mb,and with 3.1 kickstart only?
 
Could a mod please mark this request as closed; the fault now seems to be fixed so services no longer required.

Thankyou.
 
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