Vertical measure problem on Hameg HM605 - Page 1
Forum section: electronics / repair

author: Runik
author_rank: Newbie
timestamp: December 05, 2015, 09:30:24 am
content: 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 -> -11.9VThe 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=download&tx_hmdownloads_pi1=839German manual (with schematics) :http://www.hameg.com/manuals.0.html?&no_cache=1&L=0&tx_hmdownloads_pi1=download&tx_hmdownloads_pi1=1000Thanks !

author: vk6zgo
author_rank: Super Contributor
timestamp: December 05, 2015, 10:20:47 am
content: Is the -7.5V a typo?

author: Runik
author_rank: Newbie
timestamp: December 05, 2015, 11:07:05 am
content: 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 ...

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 05, 2015, 11:17:54 am
content: 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)

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 08:29:27 pm
content: This is my favorite oscilloscope, I can not help but answerI have 3 working HM605 at home...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)

author: Runik
author_rank: Newbie
timestamp: December 07, 2015, 08:52:42 pm
content: Thanks for the pointersUnfortunately 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

author: Runik
author_rank: Newbie
timestamp: December 12, 2015, 08:21:52 pm
content: 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 ?