TTi (Thandar) TS3023S noise.

[Vtile]

Hello.

It seems my 2nd hand Thandar PSU is noisier than I expected.  I always thought that it is fully linear system, but it seems that there is SMPS unit as a third output unit. The TS3022 and TS3021 supplies do not have this 5V/4A Logic output.

I removed (Desoldered the SMPS supply line from mains input end, insulated it and attached to chassis) the SMPS unit as I really do not use it and I do not atm. have interest to start to analyse if and where it does broken parts.

Now the linear part. The speck sheet promises "Typically <1mV ripple". My unit does introduce about 3.5 mV transformer and bridge noise to output. I waveform shown in this picture (signal from output). I wonder if someone with more experience can say from the waveform right away what is the source (except that it is from mains). I have faint memory that I have seen a bit similar form with a leaking bridge diode(s), but in the voltage levels >0.5 V where I typically do my electronics hobby. In the other hand I can not believe it is leaky (as failed) bridge as both of the linear supplies in the unit do show this same waveform. Maybe it is actually inside the "typical <1mV" and just randomly coupled mains noise is lifting it up (the frequency doesn't indicate that theory).

[Andy Watson]

How was the scope grounded and what signal do you measure at that ground point?
Also,  the manual says 1mV RMS.

[Vtile]

How was the scope grounded and what signal do you measure at that ground point?
Also,  the manual says 1mV RMS.

Mmm... Yep, I re-read it again and rms definedly is there. Somekind of dyslexia week going on.   With that information it turns to be about inside the typical noise level, which for clean sine would be ~2.8 mVp-p.

The scope were getting signal between PSU outputs negative and positive rail (The scope is PE connected and and PSU do have isolation trasformer). It most certainly seems to be working as should as I did go and measured the voltage on/over bridge DC points  (with no information what ripple should be in that point). Ripple is 50 mVp-p.

Some of the ripple in my first post must be from poor measurement setup. ..Or inductive coupling from the transformers.

[Armadillo]

That scope seems like a fluke scope.

In the 1st photo, you used 2mv/div, could be measuring surrounding noise.

In your latter photo, you used 50mv/div.

What output voltage was set from the PSU?

Read attached link.

http://www.eetimes.com/document.asp?doc_id=1273282

[Vtile]

That scope seems like a fluke scope.

In the 1st photo, you used 2mv/div, could be measuring surrounding noise.

In your latter photo, you used 50mv/div.

What output voltage was set from the PSU?

Read attached link.

http://www.eetimes.com/document.asp?doc_id=1273282

Thanks, I'll read that article.

In first photo, where scope were on 2mV/div (1:1 attenuation / no-attenuation ) the measurement point were from the PSU output binding posts so in that sense the normal output point. The 50 Hz ripple were also shown with 1:10 attenuation, but resolution is only 20mV/div.

In the later photo with 50mV/div and 1:10 attenuation the measurement point were over the PSUs bridge rectifier, so inside the unit before the regulating circuitry.

The output voltage were somewhere around 5 Volts +- 1V, no external load. Although I tried with 100R resistor without any noticeable difference.

You are correct the scope is old Fluke/Philips PM3390A Combiscope 200Mhz / 100MS/s.

The SMPS unit mentioned in the first post is now removed electrically and gets no power at all. It did definedly have some form of problem as it leaked to these "precision" linear outputs and also HP6632A system powersupply.  Good SMPS, no SMPS.

PS. Now looking again the first photo, the noise could be also 100Hz sinusoid (from bridge I suppose), with offset from typical 50Hz noise pick-up. The 2nd floor of this old wooden shed seems to be pretty noisy.

[Vtile]

Oh, well. It seems to me that the PSUs linear parts are working as should, atleast what comes constant load. The picture in the first picture is a real deal though, since well I made a sanity check with 9V battery. No such 50 Hz thing with 9V alkaline at all, so it comes through PSU circuitry. SMPS filth is leaking through air (or scopes internals) even to that alkaline battery measurement.
 
If this is not enough ground clip loop lenght I don't know what is. 

..And one art shot from same alkalien.

[Armadillo]

what is the 2.69mv?

[Vtile]

It is the frequenzy in 10x kHz where that specific ringing repeats, don't know where that comes atm.

[Vtile]

Found 2nd source of the 26.9kHz noise on the last artsy picture tittled "ALINE", it actually is only about ~6.5 kHz, but does have double ring about 37.17 us delay.. The one that comes faintly from the Thandar (and which hounted me yesterday several times) is repeating with 26.7 .. 27 kHz, didn't put much attention to that ring coming through Thandar (or created in) today.

[Vtile]

Yep. Got more important things to do so the yesterday eve so no pictures this time. The source indeed were found on that alkaline test. The Fluke 8030A !!

Now I can find this same frequency while probing the Thandar itself... Funny thing is that Thandars metering (volt/ampere screen) circuitry is based on ICL7016 3½-digit DMM chip ... aaaand what is the AD circuit in that angient Fluke well it is mystery inhouse Fluke PN 429100 chip, but...

paging Mr Modemhead !

You need to see this.

Here! 

It probably isn't widely known anymore, but the A/D in the Fluke 8020 was developed in a joint venture with Intersil. Then Intersil decided to market it to the world by making a tiny change to get around exclusivity...lawsuits ensued.

Thanks for clearing up the relationship of the ubiquitous ICL7106 and Fluke PN 429100.  That has always been a mystery to me!

https://www.eevblog.com/forum/index.php?action=post;quote=319430;topic=22407.0

Tada!! One source of noise is again found.. Now I can start to think how to filter it out.