Hameg 203-6 weird 50Hz signal... I think something is wrong - Page 1
Forum section: electronics / repair

author: Z80user
author_rank: Contributor
timestamp: November 30, 2016, 10:43:48 pm
content: Someone gift me this oscilloscope and I fix some capacitators on it but I see this a bit weired.The configuration now is two crocodrile wires with a resistor of 2K2 between both red wires, this noise come mostly from the channel 1 on channel 2 I get some noise but a bit lower.The oscilloscope still a bit dush outside and on switchs, I don't clear all of the switches.If I mix both channels and add the inverse of the second one I can cancel this noise.When I set high frecuency as 20us/division and ajust it a bit, I'm not sure about the exact frecuency I saw a lot of noise on it.Until now I fix some switch, create a new stop for one switch and replace 3 capacitors but now I don't know what I can do with this noise.Note: the power line is 220V and 50Hz and NO GROUND... I'm replacing the power line wired with a new one but will be in 4-5 months untils I will have ground wires, I life in a old house with wires cover by sewing thread (something like that)

author: _Wim_
author_rank: Super Contributor
timestamp: December 01, 2016, 08:10:50 pm
content: You can find the service manual here:http://elektrotanya.com/hameg_hm203-6_oscilloscope_sch.pdf/download.htmlI would check the input amplifiers first..

author: tronde
author_rank: Frequent Contributor
timestamp: December 01, 2016, 08:32:59 pm
content: User manual here (addition to previous link).https://www.manualslib.com/manual/564045/Hameg-Hm-203-6.htmlI want you to do some simple tests:Remove both probes.Turn all three red variable controls fully counter-clockwise.Time/div to 1msVolts/div to 1V (both channels)DC/AC/GD to DC (both channels)AT/NORM to ATTRIG to DCIf possible use the probe connected as 1:1CHI/II to IConnect one probe to channel 1 input and measure the output of CAL 2V square wave.CHI/II to IIChange probe to channel 2 input and measure the same.Does it look like a square wave 2 divisions high and 1 wide per period?Repeat this test with the other probe.

author: Z80user
author_rank: Contributor
timestamp: December 02, 2016, 07:46:52 pm
content: Yes, I check that before with a good quality probe of one friend and with my crocodrile probes and in both times work good, I barely need to ajust things on the oscilloscope (only on the front panel)in both channels look good.At high speed 0.2ms I see the duty-cycle is not 50-50 is more like 2.2 high and 2.7 low and I saw a vertical trace a little but not at 1msAlso I can count 11 low pulses and 10 high pulses at 1ms and saw a dot on the 11th high pulse.

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2016, 08:05:34 pm
content: Quote from: Z80user on December 02, 2016, 07:46:52 pmI Don't think too much is wrong with your scope, just use it. When you get an opportunity to check it against another do so or with a known signal from a FG.We get these questions regullarly from scope newbies and here's a recent one:https://www.eevblog.com/forum/testgear/stupid-question-sin-wave-on-dso-when-touching-probe/In short if your scope probe is not connected to a DUT the probes are acting as antennae collecting any EMI in your environment and displaying it on screen............just as one would expect.Simple test.........increase the scopes vertical sensitivity to max and just lie an unconnected probe on the bench. Now disconnect the probe from the scope.............

author: Z80user
author_rank: Contributor
timestamp: December 03, 2016, 04:21:14 pm
content: I play a bit touching the oscilloscope and place it on X/Y too with the antena wire, I saw when Dave L. Jones play with the chair and see the spikes on the oscilloscope the noise of 50 Hz here is common but I think the form of the signal can be a bit strange.I play with my fingers on multimeters too and saw the resistance between both hands is lower then between 2 fingers on the same hand if I active my musclesalso I do it with radioand my body act like a antennaif I disconect it is like a flat line, I think the form of the wave form will be more like a sinwave.. the spikes on the waveform on the top and on the botton and the noise on the middle is also a bit weired for me... well this is the first time I play with oscilloscopes

author: tronde
author_rank: Frequent Contributor
timestamp: December 03, 2016, 04:53:48 pm
content: If the signal from the CAL output looks OK I too assume the scope is OK. Spend some time and clean the front panel and knobs and start playing with it. I think the missing knobs can be replaced by something from the ELMA range. I know Distrelec stocks some, but they are not alone.Just remember that the outer metal part of both inputs and the TRIG.INP sockets are connected together and they are also connected to the mains earth (when you get that in your house).When you start to play with it, you should spend some time understanding the difference of the AC and DC position of the AC/DC/GD button as well as the AC and DC on the TRIG switch. Pay also attention to the red variable controls.

author: tautech
author_rank: Super Contributor
timestamp: December 03, 2016, 07:05:25 pm
content: Quote from: Z80user on December 03, 2016, 04:21:14 pmI mentioned EMI, it is from all the various switching devices around you and it's far more prevalent in the air than "pure" sinewaves. The fundamental frequency of what you see on a scope display is the clue, be it 50 or 60 Hz depending on where you live.