Author Topic: Vertical measure problem on Hameg HM605  (Read 1547 times)

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Offline Runik

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Vertical measure problem on Hameg HM605
« on: December 05, 2015, 08:30:24 pm »
Hi,

I just got my HM605 out of storage, and I realize it has some problems measuring vertical tension : when checking 5V DC rail of a switching power supply the trace barely gets to 4.1V.
Same thing happens on both channels.
All buttons are depressed or set in calibration mode.

I checked voltages on the Y board (expected -> measured) :
+68V -> +68V
+4.65 -> +4.1V
+140V -> +139.1V
+4.3V -> -7.5V
+12V -> +12V
+5V -> +5V
-12V -> -11.9V

The only weird reading is the +4.3V one, but the manual specifies "-12V antipole" in that case, and I don't know what it's about and if it has anything to do with my problem ...

I also checked the impact of VR501 on the YF board (ie Y final amplifier gain), but it only variates of 0.2V max, which fall far short from the mark.

Do you have an idea where I should look, a direction to point to ? I'm not an oscilloscope expert, but this problem is bothering me and I would love to be able to fix it.

For reference :
English manual : http://www.hameg.com/manuals.0.html?&no_cache=1&L=0&tx_hmdownloads_pi1[mode]=download&tx_hmdownloads_pi1[uid]=839
German manual (with schematics) : http://www.hameg.com/manuals.0.html?&no_cache=1&L=0&tx_hmdownloads_pi1[mode]=download&tx_hmdownloads_pi1[uid]=1000

Thanks !
 

Offline vk6zgo

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Re: Vertical measure problem on Hameg HM605
« Reply #1 on: December 05, 2015, 09:20:47 pm »
Is the -7.5V a typo?
 

Offline Runik

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Re: Vertical measure problem on Hameg HM605
« Reply #2 on: December 05, 2015, 10:07:05 pm »
No it's not a typo, but this specific line has a special treatment in the manual as you can see :



But I don't know if it's normal or if it has anything to do with my problem ...
 

Offline PA0PBZ

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Re: Vertical measure problem on Hameg HM605
« Reply #3 on: December 05, 2015, 10:17:54 pm »
Looks like they are trying to say that pin 9 should be 4.3V above -12, and if you measure -7.5 that is close enough (-12+4.3=-7.7)
Keyboard error: Press F1 to continue.
 

Offline oldway

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Re: Vertical measure problem on Hameg HM605
« Reply #4 on: December 06, 2015, 07:29:27 am »
This is my favorite oscilloscope, I can not help but answer  :-DD
I have 3 working HM605 at home... :scared:

A first question: is the base time correct or not ?
You can test this with a signal of a well known frequency, from a function generator for example.

If the time base is ok, look at the final Y amplifier...Is there no bad solder ? Are the signals of the same amplitude (you can mesure this with 1Khz input signal and a multimeter in ac range) on both collectors of T505 and T506? (both 2N3866)

« Last Edit: December 06, 2015, 07:36:22 am by oldway »
 

Offline Runik

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Re: Vertical measure problem on Hameg HM605
« Reply #5 on: December 08, 2015, 07:52:42 am »
Thanks  for the pointers   :-+

Unfortunately I don't have a function generator handy, I'll have to grab one before investigating further.

I'll keep you posted when I get one  ;)
 

Offline Runik

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Re: Vertical measure problem on Hameg HM605
« Reply #6 on: December 13, 2015, 07:21:52 am »
Just received my HPG1 from Velleman, so I could test the time base and you were right, it's a little off : using a 1KHz sinewave at 1ms, the 10 sinewaves are 9.8 cms in length instead of 10 cms.
Vertically, 3 volts are displayed as 2.5 volts using 1 V/div.

Is it a good idea to tweak VR303 on the TB board, or must I look somewhere else before attempting anything on this one ?
 


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