Mega ST4 working but only showing 2mb

[PhilC]

Already set to 9600, 8 N 1.

[exxos]

Did you try 1MB selection on the DRAM board ? (can't remember sorry!)

[PhilC]

Yes I did, forgot to post that.

[exxos]

Yes I did, forgot to post that.

I take it it did not help?

Are all the address and data lines from the CPU to the MMU all continuity checked ? Maybe there's a bad connection in that area. As you basely replace the whole RAM circuit and the MMU, there well be a bad connection somewhere else. I also assume you have physically checked the socket itself for damage ?

[PhilC]

No it didn't help unfortunately.

The socket did have a lot of bent pins, which I have sorted out. I am starting to wonder if this is the cause, as prior to the ram removal everything worked, albeit at 2mb. The pins as is will make good contact with the MMU but I am wondering about the MMU adaptor, as there is a gap behind each pin in the socket now.

[exxos]

The socket did have a lot of bent pins, which I have sorted out. I am starting to wonder if this is the cause, as prior to the ram removal everything worked, albeit at 2mb. The pins as is will make good contact with the MMU but I am wondering about the MMU adaptor, as there is a gap behind each pin in the socket now.

It does squash the pins little bit, but I have not really had any issues with removing the board and going back to a plane MMU. But there is indeed less pressure on the pins..

What I would suggest is you can push the pins out on the MMU itself push them outwards slightly as reinserting them in the socket a couple of times does push the pins inwards on the chip itself which can cause bad connections.

[PhilC]

You mean push the pins on the actual chip out a little?

Wouldn't have thought of that, definitely worth a try

[exxos]

You mean push the pins on the actual chip out a little?

Wouldn't have thought of that, definitely worth a try

Yes I have to do it all the time.

[scott.clifford]

Black screen with white border is exactly what I got when I removed a faulty mem upgrade and left my Mega ST1 with only 512k. It's looking for memory thst isn't there.
After I resoldered in the other 512k (making it a stock 1mb again) it ran to desktop without the black screen, white border. Only by making it 1mb

[PhilC]

Very true Scott, I dumped all 4mb and put in one of Exxos's ram boards. That Mega is suffering a lot with corrosion.