Teardown and 'repair' of a Hameg 604

• Teardown and 'repair' of a Hameg 604
  Posted by Alex on 02 Mar, 2011 20:16
• A fine piece of engineering from the late 80s.
  I got this almost for free as it was sold defective.
  
  Teardown first. The titles of the pictures are self explanatory. All old Hameg scopes have this common technique of using long shafts (sometimes 40cm) to turn pots and flip switches across the unit. Nowadays you get a front panel PCB with some serial interface to the motherboard. Back then you would not even think of running wires carrying low amplitude signals across the unit. Notice the build and 'personal touches'.
  
  http://www.flickr.com/photos/alextsekenis/sets/72157626057611761/
  
  Repair now. So this scope had an issue, sometimes the display would become a dot, instead of a line. I say sometimes, and not affected by ambient temp. Initially I thought the trigger or horizontal deflection amplifier are faulty. Then I check the X-Y mode, and sure enough the deflection amplifiers were working fine. The trigger also appeared to be working, I could vary the trigger level and the trigger LED behaved normally. The component tested which uses automatic horizontal deflection also worked fine.
  
  Cracked solder joint? Maybe! I took this baby apart and started tapping on the board with a wooden stick. Funny things happened (almost everything is analogue apart from some logic gates), but I could not reproduce the issue. I started tapping the switches, they usually oxidise after so many years. Finally, I got a glitch when I tapped next to the component text switch. Aha!  
  
  Aparently, there is a small coax cable that, for some reason, had collapsed on itself shorting out the signal to ground. Guess which signal.. the horizontal deflection ramp! Woohoo! See on the PCB, they have key signals printed on the silkscreen! Quality! To verify this, I connected the Tek DSO (now for sale) , set the function gen at 1kHz, trimmed the timebase for 1 period to span across the entire screen (10 divisions) and then measured the ramp frequency on the scope. Voila! Almost 1kHz (I had some post-trigger delay). Sure enough I could play around with that ramp with the scope's timebase settings.
  
  Wire straightened and the beauty lives again!  
  
  
• #1 Reply
  Posted by saturation on 02 Mar, 2011 20:57
• VERY nice, I think its also beautifully done inside, colorful and vibrant.  Great photos!  Thanks for sharing.
• #2 Reply
  Posted by ecowarrior on 04 Mar, 2011 19:09
• Nice electronics porn!!! Great stuff!
• #3 Reply
  Posted by Fraser on 05 Mar, 2011 10:48
• When I was a student working weekends in a local electronics emporium, I used to sell Hameg and was so impressed with them that I saved up and bought one for myself, the HM204. Hameg were a quality German product at an affordable price for the hobbyist. They seemed to have a good range of scopes to meet a broad range of needs. My scope developed a Y defection fault and was returned to Germany for repair. The service was quite simply superb ! The scope is still in use all these years later and is still one of my favourites due to it's well laid out front panel and decent performance. They look good and work just as well even when over 20 years old !
  
  I remain impressed that Hameg included a decent lissijous component tester (aka an Octopus) as standard on many of the range. This was similar though not quite as advanced as the renowned 'Huntron Tracker 1005'.
  
  I understand that Rohde & Schwarz have now taken ownership of Hameg.... they must have recognised the following that the brand had in the marketplace. The more recent (R&S owned) models appear often on e*ay with focus and display faults and I am left wondering if the new fangled 'digital' versions are less reliable or have issues with the EHT circuits used to produce the much higher anode voltages of around 12kV.  They still sell for a decent price though !
  
  I purchased a working, good condition HM604 the other day and it's great for my radio work and I have the Rigol DS1052E (upgraded to 100MHz) for the digital stuff  
  
  
• #4 Reply
  Posted by david77 on 05 Mar, 2011 13:13
• Yeah,
  
  Hameg are a superb company. Apart from good products their support is also brilliant. They have most service manuals
  available online, even for older products.
  I've rescued an old HM107 oscilloscope (all tube!) from certain death in a skip once.
  I contacted Hameg because I needed the circuit diagram to repair the thing, and somebody there even went to the trouble
  to search for the documents in his lunch break. Thumbs up!