exxos's Atari, Amiga & retro forum

stephen_usher wrote: 10 Feb 2025 13:08 I decided to have a look at my old TT power supply which failed about 10 years ago.

Doing a quick check, the PSU was continuously going into short circuit protection. Checking the rails I found the +5V to be 0.4 ohm to ground.

Removing the caps connected to this rail made no difference and they generally checked out fine. However, removing the 1640 rectifier (on the +5V rail) removed the short. It looks like one side of the dual diode has died, so I'll have to get a replacement from RS. They're not cheap, about £10.

Ouch, that is a rather expensive rectifier!

rubber_jonnie wrote: 10 Feb 2025 13:25 Ouch, that is a rather expensive rectifier!

It turns out that I misread... it was for 10 pieces, so £1 each.

stephen_usher wrote: 10 Feb 2025 13:28

rubber_jonnie wrote: 10 Feb 2025 13:25 Ouch, that is a rather expensive rectifier!

It turns out that I misread... it was for 10 pieces, so £1 each.

:dizzy:

That's more like it.

As a quick test I cut the lead on the shorted side of the diode and refitted. The PSU came up and all the voltages were good, just some noise on the +5V rail, as you'd expect if it was only getting half wave rectification. I just have to wait for the replacement part to arrive, which should be tomorrow. Then I'll have a spare TT PSU.

I wonder how often those low voltage rectifier diode go? I must admit that I've not noticed any in the PSUs I've dealt with and I don't think that Astec PSUs have them.

Well, that's another working TT power supply.


Recapped as well.

Voltages good, stable and clean.

Not sure what I'm going to do with the other 9 high current 1640 rectifier diodes though.

As I'm waiting for the rest of the stuff I ordered from Amazon to arrive I've been looking at the Tektronix oscilloscope to see if I could work out why it kept on failing its calibration diagnostics. The service manual isn't much help as it basically says, "check to see you have 12V here... If not then send the unit back to Tektronix."

I checked the 12V out from the Meanwell PSU I used to replace the damaged original and tweaked the output voltage a tad so that it was as close to 12V as possible. (I had it at 12.08V originally, now it's 12.00/12.01V)

The unit still kept failing the calibration on power on, so I put it back together. Due to the non-standard PSU I have to use a hammer to persuade the rear shield back into place. After doing some serious hammering this time everything went back and I retested... calibration successful. I can't get it to fail now, so the percussive maintenance was obviously what it needed.

Using a signal couple of signal generators I tested the system against my other two oscilloscopes. Everything checks out and the described voltages are spot on within 2 decimal points.

I think that I may swap back to using this 'scope as I can use a web browser to show the display in lieu of using a VGA cable and video capture. i'm thinking of getting into maybe doing some YouTube videos.

I do love a bit of percussive maintenance :)

Good fix on the 'scope, nice that you can get to it via a web browser, that's pretty cool.

I presume any YT videos you might do will be around repairing old computers, or will you also be covering model railways?

Both, I've created a second channel for the railways. I'm just experimenting at the moment.

Seeing as the Tektronix 'scope has VGA output I may use that with OSSC/rescaler/capture device to show the screen image. That would be live so far better than the minimum 1 second sample time on the web page (which also halts the 'scope every time it refreshes).

Looks like the capture from the 'scope VGA works well...

stephen_usher wrote: 11 Feb 2025 18:17 Both, I've created a second channel for the railways. I'm just experimenting at the moment.

Seeing as the Tektronix 'scope has VGA output I may use that with OSSC/rescaler/capture device to show the screen image. That would be live so far better than the minimum 1 second sample time on the web page (which also halts the 'scope every time it refreshes).

Cool. That scope looks great, also enormous! I also recognise that OSSC remote, I have exactly the same one :)

Are you using anything like OBS to get multiple camera feeds?

Also, what's going on with that stubby ST keyboard? Is it part of a Desktopper case?

The capture looks great BTW.

rubber_jonnie wrote: 11 Feb 2025 23:33

stephen_usher wrote: 11 Feb 2025 18:17 Both, I've created a second channel for the railways. I'm just experimenting at the moment.

Seeing as the Tektronix 'scope has VGA output I may use that with OSSC/rescaler/capture device to show the screen image. That would be live so far better than the minimum 1 second sample time on the web page (which also halts the 'scope every time it refreshes).

Cool. That scope looks great, also enormous! I also recognise that OSSC remote, I have exactly the same one :)

Are you using anything like OBS to get multiple camera feeds?

Yes, it makes it easy to do a live composite and switch between screen layouts and inputs.

Also, what's going on with that stubby ST keyboard? Is it part of a Desktopper case?

The capture looks great BTW.

The machine on the bench is my STFM with TF536 installed. I had to make an external keyboard for it from one of the damaged cases Exxos was giving away back in 2020. I can't believe that I did this four years ago!