520ST problem

[tjlazer]

Got a 520ST that was intermittantly working. Had a mem expansion card installed that clips over MMU so I decided to remove it and see if I could get it working without it. Now I can't get the drive to respond. Half the time it comes up to the desktop with no drives, (like when you power it up without a external drive hooked up) Other times get a a few bombs on the screen or just a white screen. I removed and reseated all socketted chips. Tried swapping GLU and SHIFTER chips. Anything else I could try?

[+Stephen Moss]

Any idea what make the expansion card is or what it expaned the memory to?

 

As I recall from fitting a Marpet card to my 520STfm, if you are expanding to 1, 2, or 4 Meg then you have to disable the original internal RAM by IIRC removing a few resistor so having removed the upgrade board it may be the fact that it can't find (or at least consitantly find) any RAM that is causing the problem.

My original memory expansion baord also used a socket over the MMU method and failed after about a year so if your expansion card has done hte same thing and the internal RAM is disabled then you would get the same fault with it in and out.

Edited September 14, 2007 by Stephen Moss

[tjlazer]

Any idea what make the expansion card is or what it expaned the memory to?

 

As I recall from fitting a Marpet card to my 520STfm, if you are expanding to 1, 2, or 4 Meg then you have to disable the original internal RAM by IIRC removing a few resistor so having removed the upgrade board it may be the fact that it can't find (or at least consitantly find) any RAM that is causing the problem.

My original memory expansion baord also used a socket over the MMU method and failed after about a year so if your expansion card has done hte same thing and the internal RAM is disabled then you would get the same fault with it in and out.

 

It's a Zubair Z-Ram 3d card with 2.5. I have no docs so not sure if the internal RAM is disabled?

[Christos]

Why on earth did you find the need to rip off a working RAM upgrade?

[tjlazer]

Why on earth did you find the need to rip off a working RAM upgrade?

 

Maybe I was not clear. Basic troubleshooting steps, the machine was having trouble working, and it got worse. In the end it did not work at all so I remove the memory card trying to isolate the problem. It obviosly wasn't the mem card as it still does not work in stock form.

[gokmase]

My old STe once started behaving oddly at boot time, often reaching the GEM desktop but with the drive A: icon missing. After many hours of tests it turned out that the PSU had started to wear out. It was still working, but not providing quite enough power to feed the machine.

 

Might be worth checking out perhaps, although you need to sort out any potential RAM-issue first.

[ZoggingHell]

As you said it was a 2.5mb STFM I think we ran rule out that the memory banks had been disabled as if mem serves me correctly you could only have 2.5mb if the original 512k was still working. Your ram card probably added two 1mbs. I've never heard of that ram upgrade, but if it's one with Simms or sipps you could try replacing those. Are you sure you've totally removed the upgrade and if so, have you made sure any chips you pulled on or out (a lot of upgrades needed chips on some STFMs to be pulled out) have been reseated properly and there aren't any bent pins.

[tjlazer]

As you said it was a 2.5mb STFM I think we ran rule out that the memory banks had been disabled as if mem serves me correctly you could only have 2.5mb if the original 512k was still working. Your ram card probably added two 1mbs. I've never heard of that ram upgrade, but if it's one with Simms or sipps you could try replacing those. Are you sure you've totally removed the upgrade and if so, have you made sure any chips you pulled on or out (a lot of upgrades needed chips on some STFMs to be pulled out) have been reseated properly and there aren't any bent pins.

 

Yeah this board can do 4MB, it has empty DIPP slots on the underside for another 2MB. I am not concerned with the mem board at this time, I am pretty sure it is the ST that has a problem. It use to work when I got it last year, I often had to the "atari twist" or "universal 4" drop" to get her working, but it worked and had 2.5MB RAM. It finally gave up and it now does not work at all, half the time it will boot but no A: drive. I have another 520ST and it works fine with this PS.