exxos's Atari, Amiga & retro forum

Hi all

I have a couple of STFM's and I was trying to upgrade one of them to 4mb. It has a board C070789-001 Rev.F2 with 512mb. I originally purchased a Marpet but it would just bring up a black screen so I removed it and went back to the 512mb which again worked without any issues. I have since tried the 2019 exxos 4MB from the store but now I just get a white screen. Uninstalling this would be a mission as it's soldered in and the on board 512 has been de-soldered. Looking in the service manual it basically list pretty much all the main chips as suspects.

This particular FM does have a blitter fitted.

Has anyone had this issue with this upgrade?

I have checked the 1mb resistors are installed, the 1-4 mb link is installed the MMU link wire is connected and meters out, all the ras/cas/address lines etc seem to be connected to the sockets as expected. I'm wondering if there's something else wrong with this machine as both 4MB upgrades failed with different issues.

Thanks

Brian

Have you tried it at 1MB? I know it's a bit of a faff but doable.

Reseat the ROM and bend the pins outwards in the MMU socket.

Thanks I will try both shortly.

Brian

Took out the MMU cleaned it with contact cleaner and the socket and refitted it (there was one pin that looked a bit flat but I pulled it back out).

Did the same with the glue.

Tried 1mb and 4mb

Metered out all the connections to the resistors and every resistor 59 through to 73 are connected to the PCB.

I have another STFM I might opening up on the weekend and if it's the same mmu etc I might try swapping them over just in case.

Are the ras/cas lines connected directly from the ram to the mmu?

Thanks

Brian

Found a different circuit diagram showing the mmu and resistor connections they seem fine so the mmu's connected to the 33ohm and they are all connected to the ram pcb. The ras/cas seems to check out also.

UnderTheRain wrote: ↑Mon Jan 17, 2022 10:53 pm Are the ras/cas lines connected directly from the ram to the mmu?

Those are the resistors you fit which are normally missing on the board. I assume you used something like 33R - 68R ? I tend to use 33R for everything as its more stable that way.

If everything is connected to the MMU, then really you should be working. Though these machines are that fragile, it doesn't take much for something to break. At this point you can only really try the diagnostic cart via serial link. But if your CPU or ROM is bad, then it may not boot even with that.

Also check for solder blob shorts and any broken tracks on the top and bottom of the MB.

This may help..

ooh thank you

Like I said I have another FM I might try the chips out of it. It all seems to meter out but I will go through it again later in the week or on the weekend and if not I'll grab the cart and cable.

Like I said it didn't like the other memory upgrade but worked when I went back to 512k.

Thanks for the help

Brian

UnderTheRain wrote: ↑Mon Jan 17, 2022 11:19 pm Like I said it didn't like the other memory upgrade but worked when I went back to 512k.

Marpets are evil to start with. I assume your PSU is OK and been recapped ?

Did you re-seat the ROM chips ?

Also pressing on various parts of the board while pressing reset can work wonders in tracking faults.