No line on oscilloscope ( just a point) - Page 1
Forum section: electronics / repair

author: Robin
author_rank: Contributor
timestamp: August 05, 2015, 03:27:54 pm
content: Hi guys,I’m new to the EEVblog forum, but I’m watching Dave’s videos for years now.This week someone gave me an old oscilloscope (Hameg HM412) which didn’t do anything at all.After cleaning some of the IC pins, I got it to show a point on the screen. The point does react if you probe something, just like a normal horizontal line would. The X and Y adjust also work perfectly fine.Another thing that I find weird is that channel 2 also has a point but it peaks in the horizontal way. Channel 1 peaks like normal: vertically. The scale of the Y axis is also messed up.Because the point on the screen seems be the line that is cropped together, I think it could be a setting? I’m new to oscilloscopes too, but I do know quite a bit about electronics.Do any of you know what the problem could be? Any advice is welcome!Here is a picture with it measuring 14 VDC:

author: Robin
author_rank: Contributor
timestamp: August 05, 2015, 03:31:42 pm
content: Oscilloscope on 14VDC

author: tautech
author_rank: Super Contributor
timestamp: August 05, 2015, 03:46:35 pm
content: Welcome to the forum.Check it's not set to XY mode.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 05, 2015, 03:49:57 pm
content: I don't see an XY mode switch, but I can see a pressed HOR EXT button

author: Robin
author_rank: Contributor
timestamp: August 05, 2015, 06:59:11 pm
content: Thank you very much PA0PBZ!It's my first scope, I'll learn it next year in school.This may also be a stupid question, but the scale is still another problem. If I put in 5 volts, I only see like 3mm on the screen with the amplitude set to 1 V/cm.Thanks again for your quick answer!!!

author: Paul Moir
author_rank: Frequent Contributor
timestamp: August 05, 2015, 07:13:45 pm
content: 10x probe? If so 5v becomes 0.5v at the input of the 'scope.

author: TonyPh
author_rank: Regular Contributor
timestamp: August 05, 2015, 09:58:53 pm
content: You might be better off using the square or sawtooth waveform points to see a signal.I assume hor ext is some kind of external signal so switch that off and the line too.Not sure how one would get that scope to free run.

author: Robin
author_rank: Contributor
timestamp: August 06, 2015, 06:50:04 am
content: Thanks guys,It is indeed a 10x probe so if I set the amplitude to .1V/cm it gives me 5 cm on 5V.This scope may need some ajustments, the voltage reading is not bang on. Today or tomorrow I will get my new multimeter and I'll be able to measure the voltage exactly and maybe calibrate it a little.Thanks for all the answers. This is indeed an awesome forum!

author: tautech
author_rank: Super Contributor
timestamp: August 06, 2015, 07:12:14 am
content: Quote from: Robin on August 06, 2015, 06:50:04 amCheck the Cal pots in the center of the Ch attenuators are in the locked or Cal position.Oscilloscopes are not precision voltmeters, if it's close enough, leave it well alone, you are nowhere experienced enough to adjust a CRO just yet.

author: Robin
author_rank: Contributor
timestamp: August 06, 2015, 07:28:04 am
content: OK No problem. I'm already happy that it is working now!

author: oldway
author_rank: Super Contributor
timestamp: August 06, 2015, 08:05:49 am
content: Congratulations on your new purchase.I'm sure this oscilloscope will be very useful to learn electronics.Hameg manufactured very good analog oscilloscopes with generally Philips CRT. (not on the HM412)I have many different brands of analog oscilloscopes, but my favorite for electronic repair is Hameg HM605.Unfortunately, the HM412 has no component test which is really handy for troubleshooting.Enjoy you oscilloscope, it is easy to use, perfect for a beginner.

author: dom0
author_rank: Super Contributor
timestamp: August 06, 2015, 08:23:24 am
content: Hameg used CRTs manufactured by Philips and Telefunken. I don't think they had a third supplier.Quote from: Robin on August 06, 2015, 06:50:04 amTo be expected: this scope was manufactured in the late 60s or early 70s. So it's probably around 45 years old :-)

author: Robin
author_rank: Contributor
timestamp: August 06, 2015, 09:09:48 am
content: Yes indeed this one (HM412) has a Telefunken CRT

author: oldway
author_rank: Super Contributor
timestamp: August 06, 2015, 09:56:06 am
content: Hameg has used also several other brands of CRT.For example:HM312-7 tube 130BRB31 ou 131BXB31.HM312-8 tube 130BXB31.These are Toshiba CRT's.The very last Hameg analog scoop where fitted with CRT' of Cathode Ray Technology B.V., Heerlen, Holland, a previous Philips company.http://www.crtsite.com/page3-2.html