Problem with the Hameg HM203-7

[Gwendam.753]

Hello,

I have now been using a HAMEG HM 203-7 oscilloscope for a few days. At first everything worked fine, all the adjustment buttons worked. But now I have a problem with the buttons that set the Volt/div. I connect a probe to channel 1 (on the second channel I have the same problem), I analyze the square signal 2V supplied by the oscilloscope but on the screen I observe nothing when I am in 1V/div. So I decrease the V/div rate until I get a signal for a 10mV/div setting.

Here is a picture for a 5mV/div setting:
(in the attachments)


We observe a voltage in the high state of: 1/5*5 = 1mV
However, the high voltage delivered by the oscilloscope is 2V. I may have an idea that it could come from the probe, so I ordered two new probes, because the one I was using until now is the original one so it's a little old. And I will dust off the inside of the oscilloscope, and put KF F2 for the contacts (bomb to clean the electrical contacts). Because I think there's a good chance it's from fake contacts.

Thank you for your help.

[tautech]

Welcome to the forum.

Did you check the V/div Cal knob is turned full anticlockwise (OFF) ?

[shakalnokturn]

Did the problem appear suddenly on both channels at the same time?
The service manual is around the WWW, once you have got hold of it check what supply voltages feed the input amplifiers. Check that they are getting to the amplifiers on your scope.

While you're spraying contacts make sure you give the GND/AC/DC coupling switches some. Spraying is only useful if you excersise them straight away.

[Gwendam.753]

Yes the V/div Cal knob is turned full anticlockwise. I'm sure, because if I turn the knob in full clockwise the tension (high condition) go down.

Yes, the problem is appeared suddenly on both channels at the time.
Hmmm... Lot of people said to me : "Be carefull with the oscilloscope because there are really big tensions". I'm a beginner in electronic I just know I shouldn't touch the backside of the Cathode Ray Tube and the alimentation. But on the card with amplifiers, potentiometers, that is dangerous ?
Ok so I have to spray especially on GND/AC/DC ?

Thank you for your answers.

[shakalnokturn]

No, if both channels got the fault simultaneously don't bother spraying the coupling switches too much.
Try in X-Y mode, if you're able to get sufficient deviation on the X scale that means the input section of at least one channel is good and that you have a problem somewhere between input amp and CRT "Y" plates.
If you get no deviation on X axis in X-Y mode look at input amp supplies to start somewhere.

Peak voltage in your oscilloscope is 2kV but consider anything above 50V dangerous. (Other voltages above 50V are present on X and Y output amplifiers.

[Gwendam.753]

Ok thank you, I decide to find a service to repair my HM203-7.

[Gwendam.753]

Hello,

Yesterday I received the Siglent SDS1202X-E, and I received with it 2 new probes. It was with curiosity that I decided to put a probe on the HAMEG 203-7, and I was surprised because everything works. So the cause of the problem was the probe ! 

Thank you all for the answers.

[tautech]

Hello,

Yesterday I received the Siglent SDS1202X-E, and I received with it 2 new probes. It was with curiosity that I decided to put a probe on the HAMEG 203-7, and I was surprised because everything works. So the cause of the problem was the probe ! 

Thank you all for the answers.

If you like the form factor of those 200MHz probes a bit cheaper are the PP510 probes that come with Siglent's 100MHz scopes. The US shop has them for just $10ea and you should be able to source them locally for little more.
https://store.siglentamerica.com/product/pp510-1000-mhz-oscilloscope-probe/
They should work just fine with your Hameg.

[Gwendam.753]

If you like the form factor of those 200MHz probes a bit cheaper are the PP510 probes that come with Siglent's 100MHz scopes. The US shop has them for just $10ea and you should be able to source them locally for little more.
https://store.siglentamerica.com/product/pp510-1000-mhz-oscilloscope-probe/
They should work just fine with your Hameg.

I have already bought a pair of probes on banggood for 10$ (20MHz)...
https://www.banggood.com/DANIU-2Pcs-Oscilloscope-Probe-BNC-Alligator-Clip-Ground-Lead-Test-Tool-20MHz-1X-10X-p-1157649.html?akmClientCountry=NL&rmmds=myorder&cur_warehouse=CN
When I receive them, I will analyze their quality. But many French electronics engineers advise these Chinese probes.

[Gwendam.753]

Hello,

I've received today the two probes DANIU from banggood. They work easy and well. 
I'll keep them, I think.