Electronics > Repair

Advantest R6246 "Repair" and Teardown

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42Khz:
Hi everyone,

Quite a while ago I got my hands on a "for parts" Advantest SMU, the R6246. The case had a large dent. I suspect the unit has been dropped (it weighs 33kg!), or something heavy was dropped on it.
The ebay listing indicated that display showed garbage after turning on. For this reason, I was betting on the display driver having some issue and the unit being fine otherwise.
In case anyone knows how much these units cost new, please let me know. I'm curious how good of a bargain I got.

First, the specifications. Since they are quite extensive, I'll only mention the highlights here.
Channel A:

* Banana connectors;
* Can source voltage from 620mV (10μV source resolution, 1μV measure resolution) to 62V (1mV, 100μV) full-scale;
* Can source current from 62μA (1nA, 100pA) up to 20A (1mA, 100μA);
* Maximum output power is 200W (+/-20V up to 10A).
Channel B:

* Triax connectors;
* Can source voltage from 620mV (10μV, 1μV) to 220V (10mV, 1mV);
* Can source current from 6nA (100fA, 10fA) up to 2A (100μA, 10μA);
* Maximum output power is 24.8W (+/-40V up to 0.62A).
A nice feature of this unit that I think is worth mentioning is its ability to measure either its output current or output voltage, regardless of the source setting. This is unlike my Keithley 237, which can only measure what it's not sourcing. The datasheet also claims it to be stable into large load capacitors on the higher-current settings (1mF from 600mA upward, I didn't test this), which I believe is fairly unique.

Since it was wired for 90-110V while I live in a 240V country and there were no schematics available, I decided to fully tear the unit down first. I took photographs of all the analog stuff in the process, to be able to check everything for damage and possibly reverse-engineer everything. Though I haven't gotten around to the latter.
There was no nice mains potential setting switch but the unit can be wired for 240V, so I reconfigured the transformer connections. I used seg-el's notes for another Advantest unit as a guide (https://www.eevblog.com/forum/repair/advantest-r6245-dual-channel-smu/msg3456330/#msg3456330). If I can find my own notes on the R6246 I'll post them here.
I would be amiss not to plug that thread in its entirety (https://www.eevblog.com/forum/repair/advantest-r6245-dual-channel-smu/). There, user leighcorrigall documented his own teardown and more of a sister to the R6246: an R6245 with two low-current measurement channels.

After the initial teardown and rewiring the transformer, the unit booted up. However, the display would start drawing random garbage characters and the user interface became unresponsive.
By pressing some buttons during boot I managed to get into the menu where the unit would not freeze up. At this point I was confident the display was not at fault. I dreaded the possibility of some unobtanium processor being kaput, or some EEPROM corrupted.
Fortunately, after many additional teardowns and debug sessions, I ended up finding a grand total of three bent connector pins in several of the unit's PCB cards. After I bent the last pin back in place and put the unit back together, it seemed to behave perfectly well and I have not found any obvious issues since. That was an easy fix! (which still took me several days of tracing puzzling symptoms)

To start off, here are photographs of the unit close-up, and with channel A sourcing 10V into a 10kΩ resistor with an HP 3456A keeping an eye on the voltage.

42Khz:
The most interesting parts to me were the signal conditioning hardware for the two output channels. Each channel consists of what I suspect is a controller board (which is the same design for both channel A and B) and a current and voltage ranging board. For each channel, these boards are held together with some brackets which slot into the chassis.

Unfortunately I don't have great photographs of the entire unit, this snap of the channel cards will have to do for now. You can recognize the two channels by the brackets on the bottom right. The block on the top left is the output power stage, which I'll get to. The block on the bottom left has a whole bunch of regulators and big caps on it. Beside the channel cards there is a card containing the DACs for both channels, and a card containing some digital control stuff including some EEPROMs.

I did take extensive photographs of one of the channel controller boards (identical between the channels) from both the front and back. This should enable someone sufficiently motivated to reverse-engineer most of the control loop (excluding power stage and ranging). If someone wants the original, higher-quality photographs I can share them. I compressed them a bit for the forum.

42Khz:
Let's continue with a look at channel A's (up to 62V, up to 20A) signal conditioning board. This contains (almost) all the current sensing resistors and I suspect also the voltage ranging.

We see some very large relays as well as some thick cabling. The screwed-down terminals next to the MRT-3044S relays are wired to the power stage through thick cables.
Moving to the other side of the board, we find some precision resistors and some JFET switches (2N4393). Towards the back of the board is a nice BB opamp in a can.

42Khz:
Now it's time for channel B, this is where femtoamps live. There is a big shield over the sensitive current-ranging stuff, and also one over the output connectors.
Removing the can, we see a whole bunch of teflon cups, tons of air-wiring and a bunch of reed relays, among other cool stuff.

42Khz:
Next up: the DAC board. This board contains the same circuitry twice (note the 015 and 016 towards the board corners in the photographs), with each one isolated from the other. Each copy contains a pair of analog devices AD7846 16-bit two-stage DACs along with some precision opamps from Analog Devices (OP27, OP07) and Linear Technology (LT1008) and an LT1021 buried-zener reference. There is also some digital stuff, and what seems to be a small bodge board with a NAIS AOV214 PhotoMOS relay.

The closeup of the DACs shows, among other things, IDAC and VDAC testpoints.

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