520STM vertical lines yellow and grey, no hi res

[russellnash]

Hello, recently got interested in STs for the first time since 1992 when my STE was stolen. I have a 520 STM which shows vertical yellow and grey lines and nothing in high Res mode. Reseated Video Shifter, MMU and GLUE, cleaned the contacts. Have an STF board lying around and swapped all three chips, although they are not identical from chip number. No effect. I also changed the power supply because the 12v was way too high, 17v but no change. Any suggestions welcome, thanks.

[russellnash]

Just to be clear, I do not have lines over the GEM desktop screen, I have just lines of grey and yellow and nothing else.

[stephen_usher]

In other words the system isn't booting correctly.

You could do with a diagnostic cartridge at the very least.

In the meantime you could open the machine up and reseat all the socketed chips as a first level of testing.

What you can do next depends upon what test equipment you have, e.g. good quality multimeter, oscilloscope etc.

[russellnash]

I would say not booting correctly is correct. The board is no longer in the case. I have reseated, cleaned and swapped all socketed chips. I forgot to say in the opening post that I swapped the TOS chips from the said STF board and that changed nothing. In a general forum and wider internet search nobody seems to have had these grey and yellow lines, but just because they never posted it doesn't mean it never happened. I have a basic multimeter, can test for example, for 5V and continuity. No oscilloscope.

[stephen_usher]

Well, the next step would be to get a diagnostic cartridge and something with a serial port that you can use as a terminal to connect to the ST's serial port to read the initial information it outputs.

I bet the problem is bad memory, but without any useful diagnostic tools you're not going to get anywhere.

[rubber_jonnie]

Memory would be my call too, but before going too mad check the PSU voltages are good (Only 5v is needed to boot), and get some data sheets for the RAM & ROM chips and check that they are getting 5v, have good GND connections and use your multimeter in resistance mode to check between the GND and 5V pin on the RAM and ROMs and make sure there is some resistance and not a dead short.

I think you will need a diag cart though, and I'd also suggest that you may need a serial cable as in some of these scenarios you need to hook up another machine using serial to see the output of the diag cart.

You can use a PC with serial port and software such as Teraterm or connect to the serial port of another ST that works and use terminal software.

[russellnash]

Ok thanks for the help and precious weekend time. It will take a while but I will get a diagnostic cartridge because it looks like problems will manifest themselves again and again

[russellnash]

Here is what the cartridge says:

8
I1 RAM/data line error 0000000000000000 0000000011111111 000008
I1 RAM/data line error 0000000000000000 0000000011111111 000008
I1 RAM/data line error 0000000000000000 0000000011111111 00000
8
I1 RAM/data line error 0000000000000000 0000000011111111 000008
I1 RAM/data line error 0000000000000000 0000000011111111 000008
I1 RAM/data line error 0000000000000000 0000000011111111 00000
8

How do you interpret that in terms of the cause?

[friijy2001]

I had some of these with my STFM, what I did was remove the Glue and MMU, clean the terminals and reseat it. Check the solder joints and tracks too.

Not sure if this is the same with the STM but thought I would say

[exxos]

How do you interpret that in terms of the cause?

https://www.exxosforum.co.uk/forum/viewt ... 143#p47751