After 10K

[Monotamp3]

Hi all, I require your expertise because my STF is killing me. I have an MB C070789-c1, and I installed the dual TOS with a decoder. It was working almost fine, so I decided to apply all the fixes suggested on the EXXOS forum. Everything was fine until the last one to solve the 10K nightmare.
Unfortunately, other than replacing all the SIL, I also removed the TOS sockets to lower the Dual Tos board. I wish I were clever enough to do one mod, test and then do the second, but I didn't. Now I find myself with a white screen when I turn the STF on. I checked the following:

On PSU exit, I have 5V and 12V
On the FDD power cable, I have 5V and 12V
On the video connector, I have: on pins 4 and 13 = 5v fluctuating between 4V and 5V.
on pins 9 and 13 = 15,79 Khz.
on pins 12 e 13 = 60hz that is weird because the TOS is UK.
No soldering seems cold, and on the bad-looking one, I checked the connection between the pin and the track.
I also used the EXXOS test cartridge, but still no video. And using a serial cable, on my terminal, only a weird character appears (see image).
I have attached a few images of the MB, the Test cartridge configuration and the terminal output.
I am not proud of my soldering skills, but my health conditions don't let me have very steady hands.
Only your skills can help me to try to solve the mystery

20260926_142513.jpg (199.52 KiB) Viewed 56 times

20260926_132922.jpg (161.55 KiB) Viewed 56 times

20260926_132401.jpg (472.41 KiB) Viewed 56 times

20260926_132337.jpg (488.05 KiB) Viewed 56 times

.
Thank you all in advance for the help.

[rubber_jonnie]

A white screen generally indicates your ROMs aren't working.

Since you have a TOS 1.04-2.06 decoder be sure that you are not trying to use TOS 1.04 with the TOS 2.06 decode enabled as that won't work.

If it still isn't working than I'd suggest you pull out the just the DualTOS board and try with your original ROMs.

It could be that the 2.06 decoder isn't installed correctly and has bad contacts so you may need to consider that too.

[Monotamp3]

Hi, thanks for the tips. I'll give it a try.
Quick question: does the diagnostic cartridge replace the TOS when you insert it, or does it work with it?

[Monotamp3]

Hi, I swapped the dual TOS with the old original TOS, but it acts the same.
Out of curiosity, I tested the ripple of the PSU, and it is 25mV; I suppose that's more than acceptable.

[exxos]

It sounds to me the problem started when you removed the ROM sockets and soldered the ROM board in directly ? Most probably you have a broken track or via. So you would need to continuity check between the ROM pins and the CPU..

Also note when you are testing things on your scope, of course need to be testing on the chip in itself, also be aware that pressing down on the pin could actually make contact and give the appearance it is working.. When you remove the probes the temporary pressure you put on the pen is now gone and you can end up with a open circuit.. The need to be careful when taking measurements and continuity checking..

Also note Atari motherboards do not like manhandling at all and you could have completely other unrelated bad joints which have appeared on the CPU or other chips on the board while doing all the work.

Normally a good diagnostic step is to press down on various chips on various parts of the motherboard while continuing to press the reset button to see the springs into life. You can also hold the motherboard in the centre with your thumb, and gently bend upwards each corner of the board one at a time also are pressing reset to see if that makes anything spring into life. Generally doing those techniques you can probably work out a rough area the bad connection is assuming you have one which is intermittent..