Louis Rossmann tored a fake Hakko soldering station down and was stunned to see the IC leads not trimmed, a clear sign of lousy manufacturing.
I noticed the long pins of through-hole a crystal oscillator on a 54810-66501 acquisition board, coming from a well-made Agilent/HP 54810A/54815A/54820A/54825A oscilloscope (I know people complained about these oscilloscopes, but most of the failures is in the computer section, not on the acquisition board side. I know the computer section very well, so no problem for me.)
I have a few worn attenuators and one that I received that was fried by high voltage and I tried to swap the relays. Turns out it’s not really about swapping the coil, but a near impossible precision task if you want to swap the entire block without opening up the contacts and magnet gliders. If you desolder the coil pins, you can release them and expose the inner workings:
Usually the relay coil is not the problem. It’s either the magnetic shuttle (the black stuff between the two coils) that’s not moving smoothly or the contact metal spring does not naturally bend to make good contact anymore. I fixed the first one with WD-40 (the magnet glides on a custom plastic rail), so some vertical divisions that used to be capacitively coupled (i.e. there’s an air gap instead of good electrical contact) were fixed, but it still won’t pass calibration because of the worn metal spring. Here is what the spring(s) looks like:
To put the motor coils back, I slightly push it down to the board while guiding the shuttle (that has a tiny piece of magnet in it) with a strong magnet outside the coil housing. It will fall in place easily.
Given how reasonable watronics (Bill Watry) is charging for the attenuators, it’s not worth the time, effort, and uncertainty trying to perform the surgery. He basically serves any HP/Agilent instruments that uses this attenuator hybrid that looks like this.
Bill Watry is a veteran of the 54500 series, which is the main consumer of this kind of hybrids. He’s the first person to talk to if you have any problem with HP 54500 series oscilloscopes. Please contact him directly rather than through eBay if you can, as eBay charges hefty fees (it eats up 13% of the transaction amount, not what he earned after costs).
54610B/54615B/54616B/54616C as well as first generation Infiniium uses this kind of attenuator too. I have everything needed to service 54615B/54616B/54616C except attenuators. If it boils down to attenuators, I don’t stock them and you’ll have to order it from Bill (I can do that on your behalf if I’m the one doing the repairs).
If you have an HP Infinium or Agilent Infiniium and your situation likely involves the computer section, I should be the first person to talk to, since I got nearly all the nasty quirks down over the last decade so you don’t have to spend months navigating through this minefield. The learning curve is really steep if anybody tries to figure it out on their own for the first time.
I recently bought a 1lb grab-bag of logic analyzer grabbers, predominantly Agilent grabbers. There are HP, Tektronix, EZ-Hook, ZeroPlus, Rigol and Hantek as well, plus a few random pieces like ground leads and micro-test (hook) clips.
The EZ-Hook grabbers looks very suspiciously identical to Agilent/HP grabbers, so I looked it up to see if there are rumors about EZ-Hook OEM-ing for them. In the process, I found this very useful website that tells you almost everything you can find about logic grabbers produced:
Over the last decade I was wondering if I did something wrong or my computer was infected by some rootkit that some random installation files shows up in the root folder.
Turns out it’s a stupid bug (didn’t expect something this low from Microsoft) that it unpacks temporary files of Visual C++ 2008 redistributables to whatever’s that’s largest storage space’s ROOT folder!
It’s fixed in SP1, but some old programs distributing the first revision will crap all over the root folder of seemingly random drives (actually, it’s the one with the most free space). Nasty!
I made a batch file to clean it up. It’s not robust or up to any good programming standards (should have checked the hash signature before deleting if I was paid to write that, but I wasn’t). This batch file accepts an input like where the drive letter was littered (like E:\), or without input arguments, it will just pick the root folder of the current location.
echo.Clean up Visual C++ 2008 temporary files (due to a bug)
if "%~1" == "" goto Main
cd /d %1
REM must be a root folder of some drive
REM Display current drive
echo.%cd:~0,1% drive is going to be cleaned. Press Ctrl+C now to abort now or any other key to continue.
cd /d %old_dir%
No warranty or support of any sort if you use it. That’s why I wouldn’t even make it downloadable. Just copy and paste it to a batch file yourself, and keep in mind that you are on your own.
When old equipment’s fail, they do fail in waves, depending on the failure modes induced by the original design. Last week when I turned on a TDS 784A in my inventory check, something smelled bad and the display was garbled (it has displays, but straight lines turned into wiggles).
I already replaced the caps for the processor board, keyboard and RS-232/Parallel Port module preventatively and the unit used to work fine. So it boils down to either the power module or the CRT driver.
Despite it’s unlikely to be the power module (didn’t feel any fan speed changes, display brightness changes, or hiccups in power), I used my nose to make sure there’s no burnt electrolyte smell from the power module. Indeed there wasn’t.
Sniffing can be a very valuable tool to repairs. The smell came from only one narrow area of the board so I limited it to 3 capacitors next to each other:
I took them out and cleaned the PCB and noticed that the wipes has a bit of green and black stuff on it. That’s how I can tell a capacitor just peed all over itself. The culprit is C321 and C323.
Note that the component layout for this color CRT driver, 678-1402-07 (the board has silkscreen saying 671-2373-389-1344-01) does not match the component locator I have with my TDS 544A schematics. Nonetheless, it’s nearby if you look around.
Just to confirm the capacitors I took out are the culprit, I used an LCZ meter as an overkill ESR tester to test them:
ESR for these two caps should be at the order or milli-Ohms if they were any good. I took the one next to the two offending capacitors out to test it, and the ESR looked OK so I put it back. The true reason is that I don’t have that capacitor value on hand at the time of writing, but that also helps to narrow down the true cause.
I replaced these two capacitor and the display worked correctly (not garbled). The brightness is a little bit high which can be adjusted down.
The next problem is that the shutter color changes out of sync back and forth a slow then fast rate till it gets stable after warming up for a while. I did a lot of troubleshooting, changed a bunch of capacitors and transistors and shutter board, but no avail. In the process, I smelled electrolyte evaporating with the flux and I decided to give the board a full wash with dishwasher detergent and waterpik (then dry the big part with a leaf blower, spray with 99% rubbing alcohol to the water out and left it dry). Bingo!
Lessons learned: do not leave the electrolyte leaks on the board even if it’s an old fashioned single-sided through-hole with relatively simple thick traces. I thought it’s not going to matter until I see visible corrosion, but I was wrong. Could it be the electrolytes left on the board forming weakly conductive paths that disappears when the unit warms up (the electrolyte dries up)?
In the process of replacing all the electrolytic capacitors on the board, I smelled fumes mixed with electrolytes in some areas (other than the two above). However, I didn’t record it because I measured the ESR for each capacitor that I pulled and compared to the ones I’m about to put in.
In addition to the two capacitors mentioned early in this post, here are few capacitors that the ESR of a new part is significantly lower, which might be first places to consider replacing before recapping the entire board. They are all measured at 1V, 1kHz:
Nonetheless, the only useful technique that contributed to this board being repaired is finding out where the smell comes from. The rest (reading at schematics, measuring voltages, checking waveforms on an oscilloscope, swapping out parts) are all red herrings.
In the process of troubleshooting with schematics, I also noticed that the schematic for the old TDS 544A color CRT driver is actually pretty much the same (including component numbering) as this newer board 678-1402-07 while I was troubleshooting with it.
Looks like the component layout was slightly shifted to make room a different batch of flyback transformers (there’s a riser board for the flyback transformer in 678-1402-07 used in 754A/784A). Although the component locator sheet isn’t exact, the components are within 1 inch of what’s found in TDS 544A CRT driver’s component locator. No biggie if you don’t have the schematic for the newer color CRT drivers. Just look around and pay attention to the silkscreen. Common sense will lead you to the right part.
Newer Windows, starting with Windows 7 at least, requires the clocks to be in sync for the login/authentication to work. The confusing part is that if it fails, it doesn’t tell you why, leading you to think your password was wrong.
Turns out this time, I’m trying to inject files to a Windows 2000 machine (a logic analyzer). After some Googling, this website showed me it could be a time issue. The RTC on that motherboard was alright, and showing that it’s 2018, but after a close look, the timezone was EST (GMT-7) while I’m on PST (GMT-8), so the clock is off by one hour!
I was skimming over the manual that came with my 54831M, which is exactly 54831B except they included a technical manual TM 43-6625-915-12, which Agilent basically rearranged their user manual and service manual into one book. The scope is called OS-303/G.
With this arrangement, I noticed a few bits of interesting information was buried in the theory of operation (also shown in the civilian’s service manual):
The front panel keyboard uses UART (RS-232) to talk to the interface board
The power supply is 440W
Not very useful in terms of repair, but useful if you are into modding stuff.