All you need to know about logic (analyzer) grabbers

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:

https://sigrok.org/wiki/Probe_comparison

Just in case if the website changes in the future, there’s always wayback-machine:

https://web.archive.org/web/20171011195425/https://sigrok.org/wiki/Probe_comparison

 

14 total views, no views today

Simple dialog box built in windows

Back in the days, we use “net send” to display dialog boxes (I used it to chat with my friend after we dial up to the other’s computer).

Since Windows XP, there’s a more intuitive tool to do the same. It’s convenient if you want to add GUI interactions so that the user won’t ignore the text on the command prompt screen:

msg %SESSIONNAME% "your message goes here"

 

6 total views, 1 views today

Visual C++ 2008 Redistributable (VC_RED) unpacks temp files to root folder

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!

https://support.microsoft.com/en-us/help/950683/vcredist-from-vc-2008-installs-temporary-files-in-root-directory

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 OFF
echo.Clean up Visual C++ 2008 temporary files (due to a bug)

set "old_dir=%cd%"

if "%~1" == "" goto Main
cd /d %1

:Main
REM must be a root folder of some drive
cd /

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.
pause

del install.exe 
del install.res.1028.dll 
del install.res.1031.dll 
del install.res.1033.dll 
del install.res.1036.dll 
del install.res.1040.dll 
del install.res.1041.dll 
del install.res.1042.dll 
del install.res.2052.dll 
del install.res.3082.dll 
del vcredist.bmp 
del globdata.ini 
del install.ini 
del eula.1028.txt 
del eula.1031.txt 
del eula.1033.txt 
del eula.1036.txt 
del eula.1040.txt 
del eula.1041.txt 
del eula.1042.txt 
del eula.2052.txt 
del eula.3082.txt 
del VC_RED.MSI
del VC_RED.cab 

echo.Done
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.

4 total views, no views today

TDS Color CRT Driver Repair (700 series) TDS 784A with Garbled Display (Driver 671-2373-389-1344-01 / 678-1402-07)

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:

2.4Ω ESR for the 10uF (C321)
1.5Ω ESR for the 22uF (C323)

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 perfectly. The brightness is a little bit high which can be adjusted down.

EDIT: The screen size starts to twitch and the color changes back and forth after turning on for a few minutes. It’s another problem. Another capacitor(s) must have failed. Will update the post after I got the parts and pick it out one by one.

EDIT: I replaced all the electrolytic capacitors on the main CRT driver, noting a few capacitor with higher ESR than usual (I test each removed capacitor with my LCR meter). The twitching went away, but there are random color flashes when I turned it on for a while. I’m suspecting the shutter’s clock is out of sync, which I’ll first replace the only PNP transistor in the shutter board circuit (waiting for parts to arrive).

9 total views, no views today

Windows Gotcha: Cannot access other machine because time doesn’t sync

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!

11 total views, no views today

RTFM: 54830 Infiniium trivia

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.

14 total views, no views today

HP 3560A Handheld Dynamic Signal (FFT Spectrum) Analyzer Teardown (A2 board)

I was repairing a HP 3560A that does not start up at all. The system is very modular that there are only 3 main units: LCD/keyboard/DSP board (A1), Main Processor board (A2) which manages power sources and contains the backlight inverter as well, and the analog section (A3).

Obviously the first thing to look for is where the power is managed, which is the main processor board (A2). I bought another unit (with a different defect, i.e. it boots) hoping to use it as a reference but to my surprise, the A2 board is slightly different! In fact, the LT1120 voltage regulator that I’m seeing unusual pulses in V_out pin (should be flat) is not even there!

I’ll save the repair story for another post, but for information preservation purposes, I took pictures of the two different revisions of the A2 assembly from 3 units, shown below:

  • New: 03569-66502 Rev B
  • Old: 03560-66502 Rev B, Rev C

The top part of the board is essentially the same. The new board uses Toshiba TC551001CP-85L while the old board uses Sony CXK581001P-70L for Static RAM. They are likely pin compatible and it’s just availability differences. (Ignore the randomly placed caps at the bottom of the new A2 board. I desoldered them to test if they are good).

If you pay close attention, at the top of the new revision board, it has an unpopulated DIP-8 socket and an extra 74HC174N chip, and an extra digital I/O port at the mid-bottom left edge below the SRAM. They are reserved for 3569A (a better version with a noise tracking generator) as it uses the same board. The old revision A2 board works for 3560A only. It’s a topic for another post.


The bottom part is quite different. The classical 4-diode full-bridge rectifier on the new board is not shown at the main side of the circuit board for the old A2 assembly. The new board looked much denser.

Most importantly, the old board uses MAX666 as the 5V voltage regulator while the new board uses LT1120. The pinouts are different and chip features varies a little bit, so the power management section is not topologically identical.

There are no components on the back side of the new revision A2 board (they are both supposed to be single sided PCBs), but two diodes are squeezed in at the back of the old revision A2 board, and there’s an extra resistor flyover:

My suspicion is that the diodes are intentional as there are specific through-holes for them (most like they other half of the bridge rectifier), but the resistor is an after-spin rework.


Finally, for information preservation, I also took pictures of the old A2 board (03560-66502 Rev B) from another unit I have:


If you consider the relative ease of use for less computer savvy people, 3560A/3569A is versatile yet designed specifically for the most commonly used measurements in acoustic and mechanical vibrations. It’s still excellent value for what it offers despite it’s a made decades ago since it doesn’t overwhelm you with convoluted choices so you can gets the job done once you’ve setup your recipe.

HP has designed the unit very well, with the exception of the LCD screen which cannot be found on earth, all through-hole components on single layer board and well organized structure and silkscreen makes servicing a pleasure.

I can repair and rebuild 3560A / 3569A with new battery pack and clock battery. The hardest problem to track down is no-boot, and the hardest surgery to make is the backlight. I also know how to talk to the unit from modern computers as well, so data capture is not a problem. Call me at 949-682-8145 for  consultation.

20 total views, no views today

Agilent N9304B Handheld Spectrum Analyzer Repair and Teardown

I received an Agilent N9340B 3Ghz Handheld Spectrum Analyzer with a note that it passes all self-tests but does not respond to input signals. I took the gamble that it’s the RF input connector got disconnected somehow.

I opened up the case and noticed that the 40Mhz cable was unplugged, so I was half-correct. I connected it and got a signal at the precise frequency, but the amplitude doesn’t look quite right. It’s around -20dB off. When I scanned it across the full 3GHz band, I noticed the amplitude roll-off when I scan below 800Mhz, and I got very little signal left when I get to somewhere near 10Mhz.

I tried running a user calibration with a 50Mhz CW source but it failed amplitude calibration. Apparently the unit is not fully working. No self-test errors though.

So I opened up the unit and the RF section. The front side of the board doesn’t have any visible signs or unusual smells, so I suspected the improper gains is caused by the input attenuator HMC307:

I was about to order the chip, but because of the lead time, I decided to just take a picture of everything and analyze it off-line:

After removing the screws holding the N-type terminal so I can get to the back side of the board for taking pictures, I noticed the RF out connector just fell off the board with the pad:

That means the RF out is not touching the board. I never would have suspected that it’s the problem, since this unit does not have the tracking generator option enabled and hence the RF out port is pointless. But for the sake of completeness, I resoldered the connection after I put the board and the connectors back to the RF module slab. It’s ready to be stowed away for another day when the attenuator chip arrive.

Guess what? Once I put unit back together, I turned it on again and everything works perfectly! The power level is flat and within 1dB of what my 8648C pumps out. I did the user amplitude calibration again, it passed, and everything was spot on!

My suspicion is that the path gap created a capacitor between the board and the type-N terminal, which messes up the termination and created reflections. The bottom section of this picture is where RF out meets RF in:

I didn’t study RF as my EE speciality, so if you are a RF design expert, please let me know what you think the reason might be in the comments section.

45 total views, no views today

Tektronix TDS 500~800 series Color CRT adjustments

For TDS 500~800 series, a batch of CRT driver boards, color and mono, regardless of how heavily they are used, have bad flyback transformers. After turning the unit on continuously for half a day, the screen might stretch and disappear.

If you have a matching CRT driver board with a CRT tube, I recommend instead of swapping the CRT driver (seemed more straightforward), extract the flyback transformer from the donor board instead. The reason is that the adjustments needed from replacing the flyback transformer is far less than re-tuning a different CRT driver board to match the tube.

It’s impossible to tune the CRT driver board while it is in the case, since the processor board covers it during operation (unless you have special cables for the Acq/Proc interface to replace the interconnect PCB card), it’s done ex-vivo like this:

I bought a ribbon cable extender and built a 2-pin jumper extender by salvaging them from CRT driver boards with toasted flyback transformers:

The first thing to check for is the +21V which is used to generate many voltages across the board (pun intended here): it affects brightness, scale, offset and linearity everywhere. If there’s any adjustments to be made, this need to be done first.

This voltage can be tapped by hooking the positive (red) lead to the center (output) pin of LM317 (3-pin linear regulator) at U90. If you have an alligator clip instead of a grabber, you can also hook it up to ‘pin 4’, which is the body of the regulator.

You can pick many spots for the ground pin. Since I’m using a grabber, I’d pick another big 3-pin IC sitting on a heatsink for the ground lead. In this case, it’s Q10, the transistor that drives the flyback transformer. It’s the pin nearest to the short edge of the board (behind the red lead, sorry):

Here’s a picture of blank board showing how many trimpots are there:

Only the brightness and contrast dials are documented in the service manual. The rest, I had to locate them in the schematic one by one.  Before that, I kind of figured out most of them by trial-and-error but had a few of them wrong, especially the voltages (there are three: +21V, screen and HV adj.): they all have the same effect. There are also some more obscure trims like center focus and horizontal focus (variable inductor). Now I know exactly what each dial does.

It’s hell of a lot of work to figure this out. I have some new old stock CRT straight from Tektronix at Beaverton, and it’s the reserve to support customers who bought color TDS 500~800 units from me. Almost all used units out there have problems (or going to have problems soon), and so far I’m the only one selling units with 1 year warranty (extendable to 3 years for extra).

If your unit is not under warranty included when you bought from me, and want one of these new color CRT tubes with shutter, I’ll almost require you to send your unit to me for installation unless you can guarantee that you can figure it out without my help. It’s $500 full-service with the tube included. Call me at 949-682-8145.

 

38 total views, no views today