Hoi Wong
Measurements Instrumentation
Besides mucking with electronics and modding hardware, I collect used electronic test and measurement instruments, open them up to learn what's going on inside, and most importantly, use them to make my life easier around electronics. The reason I fall in love with test equipments is that they save you a lot of guesswork.

Occassionally if I run into a broken unit (i.e. bad buys), I'll try to repair it when I feel like solving a puzzle for fun.

There are a few models with known problems at this age with easy repairs (not much troubleshooting needed):
  • [Tek TDS 400~600 digital oscilloscopes (anything that's not a B,C,D model)] the SMD bypass capacitors (for the power rail) are leaking. Wash the board with baking soda, replace the SMD caps and rewash it.

  • [HP/Harrison 6515A HV Power Supply] The tank capacitors are 40 years old. Some of them heats up and the output becomes unstable. The PCB is as simple as a high-schooler's project. No brainer to fix.

  • [Tek TDS 500~800 digital oscilloscopes] Cal initialization error means the NVRAM's battery died. Replace it and redo a SPC to get rid of the error. You don't need to save the data on it (it's just SPC and software enabling options). I know how to set the options through GPIB, so losing the data isn't a problem.

    If you have a color screen and you see weird colors, the gel dried up. You either extract a color CRT screen from a lightly used unit that are dead for other reasons or buy a LCD screen from SimmConn. Taking the gel off it is a major surgery that's not worth the time and effort.

    For example, in TDS 620A
    - Acq biard: 32 pcs of 33uF, 20 pcs of 20uF
    - Processor: 1 pcs of 10uF, 16 pcs of 33uF

  • [Tek TDS scopes in general] SPC fails usually means your attenuator relays are stuck. Luckily those relays are not custom made like HP.

  • [HP 546XX series oscilloscopes] They rarely break. If you see the screen squished, replace the small 10uF capacitor on the CRT driver board at the 'bottom'-right corner, where 'bottom' means close to the screen. Once in a while, you might want to replace the NVRAM chip (DS1220AB for 'A' models, M48Z18-100 for 'B' models)  if you get boot errors or keep losing calibration

    This model rarely breaks. Nonetheless, I've seen a rare case of each
    1) Tthe vertical trace clips to the rail: the transistor array CA3127 / HFA3127
    2) Cannot trigger properly: Replace the LM1881

  • [HP 545XX series oscilloscopes] If you see a message saying that you lost the cal, the NVRAM battery died. Some models have a silver coin battery solderd in it (you are in luck) then you can just wire your own external, replacable battery. For the rest, you need to replace the entire NVRAM chip (DS1230 is interchangable with DS1235).

  • [Agilent 5483X series or any scope/logic analyzer that uses Motorola VP22 motherboard] The IDE channel might start acting funky that it takes a few reboots to get in. The solder joint on the southbridge cracked. Have somebody reflow or reball it.

  • HP 8566A (22Ghz) Spectrum Analyzer: See Bart Kus' blog

  • HP 3560A Acoustic/Vibration Dynamic Signal Analyzer: The original power supply is 9Vac, 13.5VA, but you can actually put in DC because there's a bridge rectifier inside. The RTC battery is called LTC-7PMP (3.5V, 1.5AH Keeper Lithium Battery). Matters only if you want to keep the time for your plots.

  • VP22 Motherboard (Used in 5483XA/D Infiniium Scopes and some logic analyzers): If you have occassional problem booting (random) to an IDE drive and have random hangs if you succeed booting, suspect the southbridge chip's BGA solder joints starting to crack. Either have it reballed or reflowed.

    If you install Windows XP on it, make sure you turn ACPI on, Share Video Memory set to 64MB, and the default Infiniium Oscilloscope Software (v3.0) won't work with VP22 before AG08, so you need to uninstall it and download the latest version (v5.7) from Keysight/Agilent. You can achieve the same by using "Load Settings 2 Defaults" in BIOS setup.

  • HP/Agilent 548XX Infiniium Scopes: don't try to upgrade the processor. The motherboard is pretty restricted so the little performance upgrade is not worth the trouble. The CPU is Pentium III 1GHz, 133Mhz FSB, 1.75V (SL52R).

  • High end HP/Agilent 548XX Infiniium Scopes with 6 fans (like 54845A, 5483XA/D): if the scope shuts itself down after 2 seconds, check if more than 2 of the fans is not running. It's an zealous overheat/failure protection mechanism.

  • Agilent Infiniium 54831B/D, 54832B/M/D: If the internal CDROM drive won't boot. Check if the BIOS has disabled "IDE Secondary Slave" under the drive in "IDE Secondary Slave" (yes, it's the same name repeated in a lower level menu). This will cause your drive to be accessible in Windows but not bootable.

  • Agilent Infiniium 54831B/D, 54832B/M/D: If the oscilloscope program hangs, check if you have the old version installed. New Acq board won't run the old 3.01 software, so you need to upgrade to 5.0 software. Old board runs on both. One more tricky thing here: old board requires the old fashioned interface card (non-combo) and it will hang if you use the combo card. New board can use either. There are many old boards around, so the old interface card is better.

  • Agilent Infiniium 54831B/D, 54832B/M/D: Very often your scope program will hang if you use the GPIB+Interface combo card. The service notes and manual said it might be because your Acq board is too old for it, which is partially true. But what I discovered is that if you use a newer VP22 motherboard (or flash it with the latest AG09, some AG08 might work too, but why risk?), you can use the combo card. I don't know about the other 3-slot board (ADlink M-815G) though. It's always safe to say the old interface works on a broader range of boards.

  • LS120 Drives (Usually on Infiniium Oscilloscopes) Do not use ATAPI (JAE 50 pin) to IDE adapters on it. It will short out the adapters. Those adapters only work for CD/DVD drives.
To summarize, it's usually battery, attenuator relays and electrolytic capacitors. These are pretty much consumables to some extent.

Here are the links to people on the internet with similar interests (they are usually very experienced electronics engineer way ahead of me)
  • The Signal Path: The concepts are usually more advanced
  • EEVBlog: A funny austrailian that covers everything from beginner to expert level.
  • ルーフタワーでKW: Found it when I was trying to repair my Advantest R3131. No luck yet.
  • Kerry Wong's blog: Found it when I was researching the battery info in my 8566A spectrum analyzer
  • eToysBox (電気のおもちゃ箱): Also a big fan of Agilent/HP like me. The website has a lot of historical references as well. Just click 'English' to go to the English version of the webpage.
  • SimonsDialogs: Electronics hobby with lots of instrumentation
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