Atari mega ste help

[Tomswork]

Hello just looking for some help with a mega ste I have repaired the psu and it is working I replaced the reset switch as it looked like this

20191121_123528.jpg

I'm using a benq702 led monitor for testing I get a white screen in hi res and a black screen in low no signs of boot after 20 mins. There is sync as the monitor locks on so I'm think the cpu is halted it has memory from a working system and tos 2.06 rpms

This is the bottom of the board after the new switch

20191208_214857.jpg

The switch when pressed cause the sync to drop off

Any ideas


Thank you tom

[exxos]

The switch when pressed cause the sync to drop off

It is normal for the monitor to lose sync when the reset switch is pressed.

[PhilC]

Ok, so the first thing you need to do is clean up the pcb. Its difficult to tell what you have until all that flux or corrosion is removed.

I suggest you clean it with IPA and then see what happens.

Also, by a black screen, do you mean white border with a black foreground? maybe post a pic of the screen. Also, is that monitor 15khz capable? If not, it may not work with the Mega STe

[Tomswork]

The monitor supports all low and hi resolution modes I use it on a 1040stfm and mega st 2. The monitor shows when it has sync on the vga port and frequency. When the reset button is pressed it show loss of signal

The corrosion is a major problem that is after a cleaning is is localized to this area of the board and someone put alot of heat to the area as well

Tom

[Tomswork]

hi the screen shows no border it's all black in low res and all white in hi res

[Tomswork]

I have also had all the socketed parts out and cleaned them as well nothing seems to be hot or much above warm

Tom

[Tomswork]

Hi Philc I will get some pictures of the screen later I'm at working currently


Tom

[frank.lukas]

U309 Pin11 must be high when a SM124 is connected and low if a RGB Monitor is connected. The 74F257 can be faulty if not ...

When you change the Monitor from Mono to RGB the Computer must be make a Reset. See the Schematics

[Tomswork]

Hi frank I will take a look the u309 tonight I have a good meter and logic probe would this keep the cpu from moving to start tos. I think I have seen this syndrome as a monitor flashing on and on before on a 520

Tom

[Tomswork]

Hi exxos yes I use the same set up a 1040stfm and st2 they both lose sync until the reset is released I use this bl702 model on the apple 2e with a svga adapter and they work great

Tom