exxos's Atari, Amiga & retro forum

Hi,
So I have this STE with 4mb RAM and a dual TOS from Exxos which has always had a bad video. The screen is pretty dim compared to my other machines, in high resolution there is a lot of noise and it increases during floppy access.
Last weekend I wanted to try a newly acquired Spectre GCR but I didn’t manage to get the ST to read any of the Mac floppies (it works ok with ST floppies).
I tried an external drive with the same results and finally switched to a 520ST which read the floppies immediately with no issue.

So, dim video, floppy reading issues, video interferences while reading floppies : I checked the Phihong (recapped) PSU, but voltage is a good 5.01v dropping to 4.99v when accessing floppy(spectre GCR not plugged in). I will try with a different PSU over the weekend, but are there any other components that could cause these issues?

The only video issue I have really had is this one but you probably seen it already anyway https://exxosforum.co.uk/atari/last/VIDEOFIX/index.htm

Though there have been weird issues with different versions of the STE shifter as well.

Although I didn’t do all the mandatory fixes on this one, I had already done the ghosting fix. I guess I will use the scope to check this PSU against a good one. Annoying thing with the Phihong is there’s no resistor to adjust voltage as on the SR98 :-(

I’ll update this thread over the weekend if I can find the issue.

I did a few tests this morning, mostly inconclusive :(
I measured voltage using the scope with the following scenarios:

1. Original Phihong PSU
2. Original Phihong PSU - Disk Activity
3. Meanwell PSU
4. Meanwell PSU - Disk Activity

With or without disk activity doesn't really impact the 5v voltage (difference is below 0.01v whatever the PSU).
The Phihong still outputs 4.96v but I pushed the Meanwell to 5.10v expecting to get at least a brighter screen:
- Screen is marginally brighter, but still not on par with my other STs.
- A little less interferences in Mono mode, but still much more than other STs using the same adapter/OSSC/Monitor.
- Spectre GCR Macintosh disk reading still fails.

With both PSUs I can see around 600mV Peak to peak which seems a bit high.
I start to think that the PSU is not the issue and something is generating a lot of noise in this machine. Might be time for a full recap of the motherboard.

olivier.jan wrote: 25 May 2023 18:52 Hi,
So I have this STE with 4mb RAM and a dual TOS from Exxos which has always had a bad video. The screen is pretty dim compared to my other machines, in high resolution there is a lot of noise and it increases during floppy access.
Last weekend I wanted to try a newly acquired Spectre GCR but I didn’t manage to get the ST to read any of the Mac floppies (it works ok with ST floppies).
I tried an external drive with the same results and finally switched to a 520ST which read the floppies immediately with no issue.

So, dim video, floppy reading issues, video interferences while reading floppies : I checked the Phihong (recapped) PSU, but voltage is a good 5.01v dropping to 4.99v when accessing floppy(spectre GCR not plugged in). I will try with a different PSU over the weekend, but are there any other components that could cause these issues?

Try to do the recap of the 2 big caps on the motherboard. If the PSU is recapped it's ok, but those 2 need to be replaced as well.

I had an Mega 4ST that would be very strange with a Spectre GCR attached.

Done ALL the mandatory fixes + complete cap change, now works perfectly.

I had video (similar symptoms to what you describe) and booting stability issues with one of my STE's. Initially thinking it was a PSU issue, I was tuning the voltage up a little bit above 5v in order to get it to boot stably but even then it was only somewhat stable.

Turns out it wasn't a power supply problem, it was a plcc oxidation issue. I swapped out the shifter plcc chip to test a new one and put in some deoxit and everything cleared up and runs perfectly at stock power with both the old and new shifter chips.

Just a thought if your shifter is socketed and you hadn't tried this yet.