Electronics > Repair

Hantek DSO5102P oscilloscope PSU repair

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snoop33:
Makes perfect sense, I had N1 operating the other way round in a moment of assumption.  :-+

If the OP has burnt out those resistors (how, that's a hell of a voltage?) then N1 is toast as well.

Going back to the original question, it looks like the 5V (buck) and 3.3V (unsure) lines are drawn from the +14v supply, so if the board still works without smoking I'd look at what the 14V line is like. It may require a second DSO though! 

wasedadoc:

--- Quote from: pcprogrammer on September 15, 2022, 04:01:01 pm ---If I'm correct N1 is used to make a 50 or 60Hz (depending on the mains frequency) signal, the scope uses for something. This is also found in the newer DSO2000 series.

--- End quote ---
On many scopes the mains AC is one of the source selections for timebase trigger.

wasedadoc:

--- Quote from: snoop33 on September 15, 2022, 03:40:54 pm ---I followed the first stage through and those 6 resistors with the optical transistor (N1, PC817X) are applying a load across the first (smaller) transformer.

Being AC I would have thought the transistor would breakdown in reverse, they're usually 6v rated in reverse iirc.

Also being 6 x 15k = 90k, that's a small load to be applying across the transformer output. I don't see it being enough to make it sag (220/90k = 2.4mA).

Edit - my wild guess is with the yellow cap it's adjusting the AC phase. It handles the 110/220v switching.

--- End quote ---
@snoop33. Your VD1 on the underside is across the input side of the opto and conducts when the opto's diode is getting reverse voltage. 

The OP's board appears to have the diode in series with the opto.  Compared to yours that halves the power dissipated in the resistors. See below.

That first small "transfrormer" isn't.  It is a common mode choke to reduce switching noise going out on the AC input cable.

You wild guess is wrong too.  Those yellow capacitors are also part of interference suppression.  Nothing to do with "adjusting the AC phase" or 110/240 Volt switching.

pcprogrammer:

--- Quote from: wasedadoc on September 17, 2022, 06:12:25 pm ---The OP's board appears to have the diode in series with the opto.  Compared to yours that halves the power dissipated in the resistors.

--- End quote ---

When you take a real good look at the original posters PCB photo, you can see that it is not in series, but also in parallel to the optocoupler. It is hard to tell where the series resistors are following the traces, but probably in the same spot. The left trace coming from the input goes to the right pin of the diode, and then goes up to pin two of the optocoupler. The right trace runs below the right pin of the diode to the left pin of it and then to pin 1 of the optocoupler.

A bit strange though is that the boards are both 2016/04 Ver 1.1.

wasedadoc:

--- Quote from: pcprogrammer on September 17, 2022, 07:00:21 pm ---
--- Quote from: wasedadoc on September 17, 2022, 06:12:25 pm ---The OP's board appears to have the diode in series with the opto.  Compared to yours that halves the power dissipated in the resistors.

--- End quote ---

When you take a real good look at the original posters PCB photo, you can see that it is not in series, but also in parallel to the optocoupler. It is hard to tell where the series resistors are following the traces, but probably in the same spot. The left trace coming from the input goes to the right pin of the diode, and then goes up to pin two of the optocoupler. The right trace runs below the right pin of the diode to the left pin of it and then to pin 1 of the optocoupler.

--- End quote ---
Yes, a real good look confirms that.

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