exxos's Atari, Amiga & retro forum

If corruption is getting worse over time then it suggests a RAS / CAS connection issue.. Clean the MMU and RAM board contacts.. And try a different MMU if possible in case yours is damaged. Also check no bent pins on the RAM board or MMU.

OK, I will try that in the coming days.Thanks and happy Easter weekend.

So I tried another MMU from an STF board and just get a black screen. I use the board as spares but I tried beforehand and it booted to GEM with that chip. It is one of those silly boards that are shown in the installation guide. Cleaned it beforehand. Testing the MMU board is something I cant do 100% properly because I cant see it well enough. I looked at the diagram of the board that is in another post on the website, the purple coloured one if that helps you understand which one I mean, but I cant follow it very well either. Old eyes. :)
I haven't bent the pins on the MMU board or socket yet but I am asking for trouble pulling chips etc. in and out all over again. I have seen that spare MMUs and Shifters are hardly available, so I think it is too much risk for now. I will take a break for a while, but never say never.

russellnash wrote: 04 Apr 2021 12:44 So I tried another MMU from an STF board and just get a black screen. I use the board as spares but I tried beforehand and it booted to GEM with that chip. It is one of those silly boards that are shown in the installation guide. Cleaned it beforehand. Testing the MMU board is something I cant do 100% properly because I cant see it well enough. I looked at the diagram of the board that is in another post on the website, the purple coloured one if that helps you understand which one I mean, but I cant follow it very well either. Old eyes. :)
I haven't bent the pins on the MMU board or socket yet but I am asking for trouble pulling chips etc. in and out all over again. I have seen that spare MMUs and Shifters are hardly available, so I think it is too much risk for now. I will take a break for a while, but never say never.

The black screen sounds like bad contact with the MMU, the springs do sometimes need tweaking which I described on this post: https://www.exxosforum.co.uk/forum/viewt ... hilit=plcc

The approach of stepping away when you feel you can't do anymore is a good one though. Over the years I've pushed it and broken things because I wouldn't step away. If there is one thing that fixing up 2 Mega STs has taught me though, it's that you can and should do so if you need to. They will wait for you, it's fine.

One piece of advice regarding the PLCC chips though, is that you should get a proper puller tool for the PLCC chips if you don't already have one, and either Deoxit or Electrolube help a lot with contact problems in these sockets.

So my cartridge arrived and this what I get when I boot with it:


Without the cartridge it boots to GEM as before.

By the way I also have chip puller, which like you said, is a good idea.

russellnash wrote: 22 Apr 2021 12:09 So my cartridge arrived and this what I get when I boot with it:


EBBusError.jpg


Without the cartridge it boots to GEM as before.

By the way I also have chip puller, which like you said, is a good idea.

I'd check your diag cart is set to the correct machine type or it won't work properly. Megas and STs are the same, STE, Mega STE, TT and Falcon all have different diags and so the cart needs to be set appropriately.

If it is set correctly and still does this I'd suggest you get a null modem cable and hook it up to a serial port on a PC with a terminal prog, you may see more.

Yes, you are correct. :oops: I will have a play with the different options and give info later.

russellnash wrote: 22 Apr 2021 12:49 Yes, you are correct. :oops: I will have a play with the different options and give info later.

:)

So this what I get. I am connected to a PC via cable. I have no keyboard connected to the Atari board.


\0x00
\0xff

I6 Testing Bus Error handling
No (I6) error


Keyboard failed, connect RS232 terminal
\0x12
Mega and ST
Field Service Diagnostic Rev. 4.4
\0x06 1990, Atari Corp.
4M RAM Keyboard rev. 0 60 Hz Version 1.4 German PAL


R RAM O O.S. ROM C Color
K Keyboard M MIDI S Serial Port
A Audio T Timing D DMA P
ort
F Floppy Disk P Printer/Joy Ports H High resolution

J Hard Disk Write/Read (use SH204/SH205/Megafile)
G short BLiT test Y long BLiT test
L Real-time Clock
X Expansion Connector

Q Run all tests
Z Run internal tests (R,O,C,K,A,T,L,G)

E Examine/Modify me
mory
B Set RS232 rate
V toggle video output--50/60 Hz
? Help

Enter letter(s), and RETURN:
R

I am not going to keep swapping the display from ST to PC, but I looked at what happened after I selected Ram test from the PC keyboard and display was showing a corrupted screen like before on the GEM desktop. Regardless of what test I select nothing happens.

Can you get a picture of the error screen when you try the RAM test over serial pls.