They've responded only to some of my questions, respond according to their interest.
When the fan started to making a strange noise, I ask for a spare part and I got no response.
Even I offered paid the postage and the part, but nothing.
I'm sure, a ferrite will help to decreasing the noise. I think too that a Faraday cage for the psu board, help.
rf-loop says: "do not make noise then what need attenuate or isolate."
I see it hard, if all DC/DC converters generate noise within the same band, it would be easy to filter (input and output), but this is not the case, and -7.6V SMPS need a better filtering.
This problem needs a total redesign of the main PSU and "power subcircuits DC/DC", including the TPS40222 on the main board.
I don´t understand to OWON, spending a little more would have been a good oscilloscope.
I think that the smd solution by rf-loop is cheap, but not the best to eliminate the gnd noise, no doubt he has investigate this. But is OWON who should fix it, and offer a new psu and adapter board for free or with some discount, because many of us surely we would be willing to pay for it.
I don´t understand to OWON...
This "do not make noise what then need isolate or filter" means that need design SMPS circuits with good design practices so that they do not produce noise. This is primary rule. Secondary thing is then filter and isolate rest for make real "silence". This is good rule for acoustic noise (exaple motors) and for electronics, example PSU.
Example this experimental what I have done with PSU and Adapter board, it is only just some "what can do easy". It is NOT solution for this. These boards topology need radically change before it is good.
Today I do not know what kind is Owon new PSU what is going to mass production somewhere around start of June. And what changes they have made for adapter board (what is still more easy).
About fan. Just I heard one person who have bad fan and he call Owon and no any problem. Owon send new one.
If you have warranty failure in your scope, ask Owon start RMA procedure for get it repaired.
(in case that you have international "overseas" warranty.) Of course primary roadmap is contact seller. Why he sell these if he can not give any kind of after sales customer care. Or was he only "box shipper". If this is case... you have get what you have paid. If example my customer is troubles (example failed fan) and if he want new fan from Owon and he want himself change it. If in this case Owon do not help him I take contact to Owon an ask this help to him. You know, all this is work. More or less. But my customers have allready paid some amount of after sales customer care.
Common opinion
I wonder more and more this situation. Peoples buy from whoever box shipper example oscilloscopes. This box shipper seller do only that he receive boxes wrom some source and then he reship these to customers who buy. Then, what ever happends these customer are alone. Thenh all these customers want help directly from factory.
What other business go like this? Buy bicycle... if troubles, who help... factory? If buy car, then some trouble... customer call with phone or letter to factory who have made this car? ... you buy Sony or Lg TV and then there is problem... all peoples call directly to factory?
Oh boys this do not work...
Some yars ago I buy camera, Canon.. then there was problem with it. Oh yes I send letter to canon factory secretary and ask factory help me. No no.
I call to seller and ask help. Kindly seller tell me how to do do.
I do not understand how this oscilloscope or other measurmenet equipments situation have gone to this position where we are now.
I have one recommendation to Owon. This is public recommendation.
Do not sell these equipments to "whoever".
Sell these only to these distributors who really also do they jobs and add some value to product. Product is more than only box. It include box itself but also some kind of pre- but more importantly some kind of aftersale customer care - even some amount. Just like some brands do.
Stop totally this wild markets!
Then give all and full support for distributors - even some spare part lots. Even some teaching about products and some basic service information so that distributors really can give after sales support and add some value to product.
Organisation where all can be reseller (or better say: box shippers) and then all end users ask customer care from factory - in long run it is road to dead. It do not work. These box shippers can not give any value to end users. They make only finally this all business impossible.
If do not want this solution where all win. Triple win. Customer win. Dealer-distributor win and Owon win in long run.
In other case it is best that only who sell these directly to end user is Owon itself. And same recommendation to many other manufacturers. You need develop organisation.