Hameg HM400 Oscilloscope issue  - Page 1
Forum section: electronics / repair

author: sprit
author_rank: Regular Contributor
timestamp: January 15, 2023, 11:28:26 am
content: Hi everyoneI have an old Analog Oscilloscope. Currently it is having some problems. Now it shows only half of the screen. I can't edit the XY part. Removed the source part and HV area of ​​the CRT. when I switch back to x10 mode the waveform appears full but I can't adjust the beam up and down. I couldn't find the Service Manual of this model on the internet. Do you have anyone? Looking forward to all the helpers.Youtube Link for the video.https://youtu.be/o89RQ1vAbjAThank you very much and have a nice day everyone.Regards

author: jonpaul
author_rank: Super Contributor
timestamp: January 15, 2023, 12:25:37 pm
content: easy to find schéma use Google.Most Hameg HM get blown Zaxis or CRT ckt HV as they age.I suspect the CRT pins or socket may have become loose or corroded.Pull the back panel to see it.Beware of the stored CRT HV, even when turned offJon

author: sprit
author_rank: Regular Contributor
timestamp: January 15, 2023, 01:08:57 pm
content: Thanks John.I've checked all. The CRT work fine, the problem happen only when i change to X1 mag on oscilloscope. Idk whre to check now. I've search the service manual but still dont see this model. Sorry, my English is not good.Regard

author: Swake
author_rank: Frequent Contributor
timestamp: January 15, 2023, 01:20:22 pm
content: Cannot find the manual either for the HM400.HM404 and HM408 is out there, but is not the same generation so cannot be used as an example.If you know where to find the schematic please share the file or link.

author: wasedadoc
author_rank: Super Contributor
timestamp: January 15, 2023, 10:43:21 pm
content: https://www.eevblog.com/forum/testgear/hm400-oscilloscope-service-manual/msg3575381/#msg3575381Seems that even an insider (Rich) couldn't help with a previous request for this manual.

author: jonpaul
author_rank: Super Contributor
timestamp: January 16, 2023, 12:00:39 am
content: try contact cleaner on the X1/X10 switch, on my HM203 and HM103 every switch and control pot needed lube and exercise.Jon

author: sprit
author_rank: Regular Contributor
timestamp: January 21, 2023, 10:10:21 am
content: sorry but i need your help. Yesterday I tried to replace a couple of HCT4094s on the front panel, but I mistakenly removed another HCT138. Here is a picture of it. I forgot their location. I'm so stupid. So can anyone here with this scope take a picture of their location for me? thank you very much.

author: Hamelec
author_rank: Regular Contributor
timestamp: January 21, 2023, 05:13:37 pm
content: ask (friendly!) for a service manual:customersupport@rohde-schwarz.comor directHeinz.Semmerow@rohde-schwarz.com

author: Swake
author_rank: Frequent Contributor
timestamp: January 21, 2023, 10:15:37 pm
content: Quote from: sprit on January 21, 2023, 10:10:21 amDo you mean that you do not know the orientation of the chip?You can find the orientation if you trace GND and Vcc on the PCB. For the HCT138 GND is pin8 and Vcc is Pin 16.On logic 74xx and 40xx chips GND and VCC are always in the same corner of the chip.

author: sprit
author_rank: Regular Contributor
timestamp: February 02, 2023, 09:59:28 am
content: Finally after many failed attempts, I found the problem. It's because of this little transistor. It converted to diodes, which was a surprise. i tried replacing it with an equivalent transistor and problem solved. I have placed an order and this transistor will arrive in a few days. What a tough job!

author: sprit
author_rank: Regular Contributor
timestamp: February 02, 2023, 10:01:06 am
content: BFG135 Failure

author: sprit
author_rank: Regular Contributor
timestamp: February 02, 2023, 10:02:15 am
content: Now its become ok. Wait for components arrive

author: Swake
author_rank: Frequent Contributor
timestamp: February 02, 2023, 11:31:22 am
content: The meter shows the junction between pin 1 and 2 is shorted. Good catch !