Help bringing my 1040STf back to life

[exxos]

Perhaps i'm wrong but the measures I get would say that there is no cut tracks on the board.

How do you know what is driving the bus, MMU ? CPU ? Buffers ? DRAM ? Even a cut track will still be driven by something. Even a floating signal can still give a voltage. So the tests are just not valid. Even with a scope its very hard to debug.

If the MMU can't get correct data back from the DRAM, it marks the bank as bad. Regardless of what you measure, how do you know what bits are faulty internally on the DRAM chips ?

So in your opinion does it worth a try to your 4MB upgrade (STFM 4MB RAM EXPANSION) ...

Adding more potential issues onto a board which is already malfunctioning isn't a good idea.

[PaulJ]

Your meter cannot respond to the speed of signals on those lines not to mention they are not consistent signals and they will not appreciate the load the meter puts on them. Your efforts with a meter beyond power supply voltages and chip power are useless. If you want to check for opens power off the machine and verify resistances pin to pin via info you gleen from the schematic.

[PhilC]

Another suggestion, buy a working 1mb motherboard and use yours to learn electronics by fixing it at your leasure.

[doc]

Ok thanks you all.
So I give up

[exxos]

Why didn't you consider what I suggested in my earlier post ? viewtopic.php?f=23&t=1653#p25439

[doc]

Ok I'm gonna try to change the DRAM bank ... need now to find sockets and chips. Any advice where to buy them will be appreciated. Do you sell them ?
I'll keep you in touch for the results ...

[exxos]

Ok I'm gonna try to change the DRAM bank ... need now to find sockets and chips. Any advice where to buy them will be appreciated. Do you sell them ?
I'll keep you in touch for the results ...

I do sell tested chips here https://www.exxoshost.co.uk/atari/last/storenew/#0111 I don't sell sockets though, but I strongly recommend you use them, and even get a diagnostic cart. https://www.exxoshost.co.uk/atari/last/storenew/#0165

[doc]

A bit funky to desolder the bank. I'm waiting to seek good soldering materials...

[exxos]

A bit funky to desolder the bank. I'm waiting to seek good soldering materials...

Cut the pins of the chips, then you can desolder one pin at a time.

[doc]

Success !!!
Thank you evereyone for your replies and advices to my memory trouble. I finaly succeeded in changing the faulty DRAM bank thanks to Exxos ram set. It was rather difficult to unsold the chips. I used a desolder pumping station to archive that, but even with this efficient material it was hard to get the chips out of their holes (I destroyed one of them !). Yes i could have cut the pins and then desolder them out but I wanted to preserve the chips as much as possible in order to test them in case of success.

So I desolder the bank, soldered brand new sockets and plugged the new DRAM in. And voilà ! my 1Mo memory is back !!!

IMG_4234.jpg (117.04 KiB) Viewed 470 times

I then tested all the chips one by one, by replacing them one at a time into the new bank. Thanks to the diagnostic card I found only 2 of the chips (upon 16) where out of order.

IMG_4232.jpg (210.27 KiB) Viewed 470 times

Plus the one I destroyed...

Added a brand new 1.4 TOS.

IMG_4231.jpg (147.34 KiB) Viewed 470 times

And here is my baby

IMG_3332.jpg (131.31 KiB) Viewed 470 times

Thanks again everybody !