HP 3456A Digital Voltmeter
A very long time ago, I bought a venerable HP 3456A Digital Voltmeter. Back then, I had no clear idea what kind of device it is; but it was cheap. It worked quite fine (it is indeed not calibrated), but I noticed for a while that it was quite unstable …
HP 34970A Data Acquisition Unit - communication protocol
In order to build a replacement display for the HP34970A data acquisition unit, I needed to understand the communication protocol between the CPU board and the front panel assembly.
General description
The unit is built with four boards:
- A1 is the main bard, with the PSU, the main controller and …
HP 34970A Data Acquisition Unit - part 4
After a summer pause, I'm back on my HP34970A repair project. In the previous post in this series, I've started to reverse engineer the serial protocol between the CPU board and the front panel, and implement a prototype of replacement display.
OLED display
I bought the bigest OLED display I …
HP 34970A Data Acquisition Unit - part 3
As explained in the previous post in this series, I've started to sniff the serial protocol between the main board and the display panel so I can replace the failed VFD by an OLED or TFT display managed by an arduino or similar.
Protocol
The serial communication takes place at …
HP 34970A Data Acquisition Unit - part 2
This is quick follow up of my previous blog post on my attempt to fix my recently acquired HP 34970A.
In my hurry to replace the failing FRAM (FM24C04) chips, I also replaced the FRAM chip on one of my 2 plugin modules.
Bad idea: the module then provoques an …
HP 34970A Data Acquisition Unit
I recently "scored" a HP 34970A with the DMM included and 2 plugin cards (HP 34901A and HP 34907A) for less than 200€. The plugins should be in working condition, but the main switch unit was almost "given" with the plugin modules since it is non functional.
It's in very …
Tektronics 2445 scope PSU repair: part 3
After having mostly destroyed the PSU of my Tek 2445, I've decided to be a bit less foolhardy and I've subscribed to the yahoo Tek group. I discovered that such a failure has already been reported there, also after a full recap of the preregulator and regulator of the power …
Tektronics 2445 scope PSU repair: part 2
After a quick repair of the PSU of my Tek 2445, I've started a more systematic replacement of the capacitors.
But I was also a bit worried because of a dirty noise coming from the preregulator area.
After having replaced most of the electrolytic capacitors, the dirty noise became louder …
HP8904A Multifunction Synthetizer Repair: 10MHz output
After having fixed the PSU of one of my HP8904A signal generator, I discovered that the other unit had its 10MHz reference output dead flat.
I've disassembled the main logic board, but unfortunately, the schematic of this later A2 board (as it is referenced in the servce manual) is notavailable …
HP8904A Multifunction Synthetizer Restoration
What Is This About
I have a couple of HP8904A multifunction synthetizers for years (bought them on ebay around 2007 IIRC). One of them is working properly, but the second one had very inaccurate output levels, generating a non-symmetric signal when output level was set above 5V or something like …