Agilent U3606A teardown (partial)

[anotherlin]

Hi everyone,

You may remember that I posted a topic about having noise on my U3606A. This issue hasn't been solved. I've even sent it back to the retailer's customer support which told me that it cannot found "noise". The DMM part is working perfectly though.

Anyway, I decided to open it so we can all have a look.

To sum-up, the U3606A is Bench DMM along a 30W PSU (8V/3A or 30V/1A) :

http://img853.imageshack.us/img853/6929/img1091vu.jpg

Here's an overview, front is at the right.

You can see at the left (back of instrument), that it has switch mode power supply. The 30W power supply seems to be using a switch mode "pre-regulator" followed by a linear "post-regulator". More on that later.  On the bottom left, there is the National Instrument chip controlling the GPIB. The USB controller is on a PCB below it. Note that the "digital" PCBs are physically separated from the PSU.

You can see on the right the DMM part, it is shielded from the PSU by a metal sheet. There is actually two PCBs, one on top of each other. Because I would have to remove all connectors and because my unit is working well, I didn't took it apart.

http://img88.imageshack.us/img88/9168/img1096q.jpg

Let's start by the PSU/Computer connection.

So it is a power supply unit and the PCB is "through hole", not much to say. Except that it is well packed, and according to the board I have revision 001.

The GPIB is "classic" with a National Instrument chip along with the SN chips for signals. I didn't bother to look at the USB controller, but I guess there's nothing fancy.

Now for the PSU part of the instrument. Like I said before, it seems that it still have a linear regulator after the switch mode PSU. In particular, look at the iron heatsink, there is a 2N3055. I guess it is the "series pass transistor", there are cables that take it to the front part then.

http://img15.imageshack.us/img15/8225/img1094hv.jpg

I'm no expert in PCB design but looking at the placement of this 2N3055 transistor, I'm wondering if it is properly shielded from the noise of the switch mode PSU ? There is an inductor in front of it ! And there is the GPIB/USB digital I/O behind ? Maybe that's why I have noise on my output ?

http://img547.imageshack.us/img547/615/img1103i.jpg

Now, let's go front side. So we have all DMM stuff. It is all SMD, so there is not much I can say. And in particular, everything seems to happen on the board below (more on that later). But you can see on the right, the input cables. The big resistances are probably for voltage and current sensing of the PSU.

http://img201.imageshack.us/img201/9929/img1093fg.jpg

I didn't remove the top board, but I was still able to take a picture of the board below. As you can see, there is a shielded box. I guess it's probably there that the DMM does the measurements.

http://img339.imageshack.us/img339/5983/img1097oc.jpg

To end-up, here's a pic of the front panel, nothing fancy.

http://img534.imageshack.us/img534/9269/img1102ur.jpg

And that's all. Agilent bought a taiwanese company, and they made the U8001 and a few other instruments rebranded as Agilent. I'm wondering if the U3606 is one of their job. The PSU is definitely not E36xx series style.

Best regards,

[anotherlin]

Here's the topic about my noise problem :

https://www.eevblog.com/forum/reviews/agilent-u3606a-%28dmm-dc%29-noise-on-dc-output/