Issue with the STM 4MB RAM UPGRADE

[exxos]

If you honestly think the board is faulty, then I suggest removing it (as your heading towards doing that anyway it seems) and then check resistance on the board for RAS0 and MAD9 and see if you get the same resistance on the 4MB board when its out of the ST. If you don't, then the short must be on your ST somewhere.

I don't see how it's even possible as these are highlighted RAS0 and MAD9 on the PCB. They are not even close.

Capture.PNG (68.38 KiB) Viewed 3011 times

Also you don't need to connect MAD9 for testing. It would just result in 1MB RAM not 4MB.

It would also help if you post clear images of everything and how you got it all wired up.

Also it's not clear what you are saying with the diagnostic cartridge. You use it over serial link to a pc and you can test the ram easily. How to use the cart is posted in the basic troubleshooting section on the forum.

[Malichite]

OK will do, I'll remove the upgrade board and do as you suggest and see if I can verify the issue is with the module itself or something else. Not that they differ from your example, but I'll post the images of the fr/bk connection. My wiring is BLK is MAD9, BLU is CAS1H, GRN is CAS1L, and YLW is RAS1.

Also it's not clear what you are saying with the diagnostic cartridge. You use it over serial link to a pc and you can test the ram easily. How to use the cart is posted in the basic troubleshooting section on the forum.

OK I've never used that and didn't realize it was a serial link to PC to pull up more info. I was thinking that was something that was run directly on the ST. I'll take a look at that forum to assist me.

[rubber_jonnie]

Details about using the diag cart, including the use with a serial cable, can be found here: Diag cartridge basics

[Malichite]

So first off the STM Memory Upgrade I received came with nothing more than the two memory chips and a couple of resistors and caps populated. As part of the installation I added headers to all the through-holes and I didn't notice any special comments about the MAD9, CAS1H, CAS1L, and RAS1 except the comment to solder directly rather than using the black end connector on the supplied wire. However after tracing the reason for the short from MAD9 to RAS0, it's related to the through-hole header that attaches to the motherboard below. The placement of the MAD9 through is directly above pin 4 on the memory chip which is the common RAS line and the reason it wasn't a dead short at the MMU was related to the 68R added to the RAS0 line to reduce ringing.

So is the correct way to install this to remove the header below the MAD9, CAS1H, CAS1L, and RAS1 through-holes (if so, why not just make these pads instead) or is there some other compatibility issue with my motherboard revision (C070243 Rev H)?

Included an image of the debug work on the short I was seeing.

[exxos]

I'm afraid you have lost me. I get the impression you soldered those 4 jumper wires via header pins to the MB ? In that case you have shorted out those 4 signals to whatever is under them on the MB. Those 4 pins are wires not headers.

I suggest you follow the instructions here https://exxosforum.co.uk/atari/last/STM4MB/index.htm as it clearly shows the 4 jumper wires and locations to solder them. If you have headers to the motherboard as well then no wonder your having problems.

[rubber_jonnie]

OK based on your photos and description, I think what you've done is solder a 4 pin header through from the expansion board where the RAS1, CAS1L, CAS1H and MAD9 wires are supposed to connect, down to the matching holes in the space for the socket below the expansion board in that location.

The instructions don't say to do this, they show a header on the expansion board only for connecting the 4 wires.

As I understand, this is incorrect, so you need to remove those 4 pins as they do not connect down to the mainboard, what you've likely done is cross connected RAS,A0,A2,A1 to MAD9,CAS1H,CAS1L,RAS1.

A photo looking from the front edge directly between the 2 boards at where the wires connect should verify if this is what you've done.

All that should be connected to the 4 holes on the expansion board are the 4 wires for RAS1, CAS1L, CAS1H and MAD9.

[Malichite]

Care to point me at the line that says don't do this on this page?

Original_STM_update_instruction_as_of_2-18-24.jpg (248.04 KiB) Viewed 2966 times

Closest I found was:

I then suggest fitting the fly lead cables next. There are four wires to solder and I suggest you solder the wires directly on the board and not with the black end connector housing as I did in the above image.The wires supplied will be random colours!

To which I did just that, tied the connection from here to the back of the MMU since I didn't pull up the memory pinout until I was debugging. I say no where on that page of the supplement that said "DON'T PLACE HEADERS FOR THESE PINS" and looking at the pictures that also isn't evident.

Oh I see you now just added that comment as I was responding, so I guess I'm the one that doesn't read...

New_STM_update_instruction_as_of_2-19-24.jpg (296.24 KiB) Viewed 2966 times

Hopefully that save other poor saps the hours of debug...

Thanks,

[rubber_jonnie]

OK, so I can see you are annoyed, but I have spent my valuable time working with @exxos this morning trying to understand what has happened and help you, so please try and be a little more accepting that at least we have tried to help and have used the experience to remedy the situation so that nobody else falls foul of this again.

In addition, exxos has revised the PCB layout to make this very difficult to do physically in future.

There are other forums and suppliers that simply wouldn't take the time to help and would leave you stumbling around in the dark once they've had your money, something we try very hard not to do.

Whilst you state "Care to point me at the line that says don't do this on this page?", I can't on the original page, hence why we have changed it.

You also ask where it states "DON'T PLACE HEADERS FOR THESE PINS", but it doesn't say to do so either, and it in fact shows a header on the topside of the board to which the wires are connected rather than headers going through to the mainboard.

How would you fit a header both to connect the plugs on the wires in the photo and also go through to the mainboard, unless they were incredibly long?

Also, based on the RAM IC pinout, why would you ever want to connect RAS,A0,A2,A1 to MAD9,CAS1H,CAS1L,RAS1?

Be happy that there are people willing to give their time and that are prepared to help.

You have managed to effect a change for the better, and we hope that this will allow you to get your expansion up and running now.

Please let us know how you get on, we are still here to help.

[rubber_jonnie]

@Malichite Just wondering how you got on with your expansion board and removing those 4 header pins?

Are you up and running now?

Thanks.