Advantest R8340A Picoammeter, High resistance meter review

[DaJMasta]

The updated file appears to be fine, and serg-el's is appreciated as well!  Mine is an R8340A, but it had the B01 firmware on the digital board, it could just be that yours has a more recent version.  My unit's SN is 43030012 and from the chips on the boards that I can see, it looks like it was probably made in the very end of 1993 or early 1994.

[DaJMasta]

Finally got the chip in yesterday and had time to program and insert today, and there's an improvement but no fix yet.  I've tried both the 2.01 and 2.53 firmwares and they yield the same Error 4, which indicates problems talking between the internal CPUs (presumably just the analog and digital boards), and since I've had a result from replacing a 74 series chip already, I have a few more to check, at least.  I do know that the optical transmitters and the analog board CPU are active, at least, so it is probably the connecting logic.

By the way, using a Flash based SST 27SF512 EEPROM seems to be a fine replacement for the original MBM27C512-20 EPROM.


Since we've got a little ROM repository going here, I found my analog board had a different firmware version, C00, so I've attached an image of it.

[PartialDischarge]

My U40 IC also has version C00.
The unit I have broken starts fine and can put out any voltage, but won't take readings, showing some incoherent things in the process. When I have the time I'll replace all the logic side chips in bulk, or at least most of them, shouldn't be very expensive. Its faster than probing around.

[DaJMasta]

Been trying to troubleshoot this Error 4 problem and have run into some interesting things.  I'm wondering if you could read and upload the C00 firmware for the analog ROM, or at least verify that the checksum is 0x00EB 98D8.  I've been checking all the connections I can between the two chips and haven't found the culprit yet, but I found that flashing the older B00 firmware to the replacement ROM chip just caused the relays to thrash on power up - very unhappy.  I don't have an error message saying that the Analog ROM is bad, and there is one mentioned in the manual, but I'm suspecting it because I haven't be able to ID an in between component acting bad, so I'm wondering if the ROM is damaged in a way that's just keeping it from responding.  The mark near the digital side regulators on the silkscreen says the design is from 1990 and is numbered BLR-015631, perhaps the B00 firmware is only compatible with a different board revision.

I've been able to see activity on both transmit sides of the optical link, but I haven't pulled the mainboard out (lots of screws and bits mounted to things), and I haven't been able to trace the receive path (I think I've found it on the analog RX side by shining a bright light and looking for the trace on the underside, but no guarantees).  Thanks to a bit of paint and a strange part number, one DIP 8 on each side is the LED driver, a TA8513P, marked TOIC8513P, was tough to ID, but  they both seem to be operating on my board.

I also thought I had a glitch chased down to the MB8873H we had very little information on, but through matching some pinouts and searching around with MPU compatible chips, I think it's functionally the same as the much more common HD6840P PTM.  I will try both side by side with a functional unit when I can get it working, but at least right now the symptoms are the same using either chip.

It also appears that there are some cycles when the data bus is fully released - I had been seeing lower pulses only a bit over 4V, but they seem to be occurring when nothing is actually driving the line, so it's sort of a parasitic pull-up.  I think it was seeing these on the scope that pointed me to the PTM, which seems to be working.  In testing, I also found that you could just power up and probe the CPU board on its own, and these runts don't appear with it running in isolation.  I've also seen some real weird outputs from the 7489 memories on the mainboard digital section, but they seem to be unconnected, so I don't think they're malfunctioning.

[PartialDischarge]

The revision of my board is the same. attached the rom and a picture of the back of the board so you can follow traces easily.

I had a similar experience as you with the CPU board of my 3458A, and I had the schematics. Weird traces and signals, with shared buses thats normal. Eventually the board was fine and the fault came from a CPLD in another board, my point is that prepare to change most of the logic, otherwise its very difficult to pinpoint faults in digital boards, more so than in analog ones.

[DaJMasta]

Thanks, for both!  Interesting developments but no fix yet.

I tried your C00 r1 firmware and the checksum was indeed different, but using it resulted in the same relay thrashing - it wasn't happy.  So I reverted to the original chip and went back to tracing out the communication paths.... and both work.  In each case, the aforementioned DIP 8 driver drives the TX LED and the return signal goes through a 74HC04 and then into pin 11 of the main micro - I was wondering what their scheme for serial decoding was, turns out they just use the micro's SCI interface on port 2.

My symptoms have remained constant, some bi-directional activity on the optical lines and then a bunch of dead air, and after some timeout of showing the version numbers on the front (big digits for logic ROM, small for analog ROM I believe), it shows error 4 and then restarts.  I think that probably points to some sort of hang on the analog micro side, but I'm not exactly sure where.  Will try to look into activity on the chip in that dead air time, or if it's just idling or hung up on something.  If that doesn't work, I may swap in one of the thrashy analog ROMs and try to see how those relays and such are being switched, then trace that back to see what on the MCU is making it actually happening and try to verify those chips are all functioning.

[serg-el]

Check the power and processor board

[serg-el]

Check three consecutive resistors. Burn often.

[DaJMasta]

Much later, I've returned to my repair because I managed to find a working (or at least mostly working) unit for a reasonable price for direct comparison debugging.

I did some testing on the new unit and found it to be function except for above about 150V on the source - it flashes error HV and occasionally KV on boot but always passes the self tests, but when measuring the source, 100V is fine, but set at 1000V I can only get up to about 150V settled on the output before it gives up and goes into discharge mode.  There's also an unsettling ozone smell that starts when at those higher voltages.... I had assumed dust, but have since convinced myself otherwise, and it even has the smell before the front connectors are energized.

Surprisingly, there were some hardware differences - exactly the same boards and revisions, but some parts in different packaging (the ADC is in a block module that fits in the same DIP socket), and some parts different altogether including some darlington transistor array chips which are an equivalent chip under a different part number and manufacturer.  The firmwares on it were 2.01 and 3.00, even though the serial number is much more recent (7303 instead of 4303).

In any case, the unit boots past the Error 4 I was seeing on my original, so I started probing.  I compared the serial data over the optical couplers and saw similar initializations and replies, so I started probing the data buffers and stuff to try and sniff out activity on the working one and compare it to the one that didn't finish booting.... I probed on the DAC and ADC too to verify something was happening, and to my surprise, it all seemed to be acting normally, it just eventually hung and rebooted following the Error 4 message.  It even appeared to be executing the self tests of the parts, it just wouldn't progress to the final stages.  Running out of ideas for the night, I figured I'd try to swap the CPU board between them just to rule it out, since from probing months earlier I knew the serial lines between the two CPUs are basically direct (all the circuitry under the CPU board is for rear outputs)..... and the old one booted up fine and was able to measure.

With the new breakthrough, I took a thermal image of both boards when running and the big standout was on the dead one, that timer chip suspected earlier was much hotter.  What's more, it's a new part number on the working board... so that misc timer chip suspected to be 68000 compatible but which we had no datasheet, now has a drop-in replacement!  The MB8873H on the old board was an HD63B40 on the new one!

Datasheet available, supply available through ebay (though no one who can get it to me for two weeks) so I have a clear direction forward with the repair.  I figure once the older one works, I'll start probing it's HV generation side to fix the HV/KV range errors on the newer ones (though I suspect with the ozone smell, the thermal camera should shed a lot of light too).


In the time I was playing around with the new one, I couldn't use the highest test voltage, but I had fun measuring the resistance of a post it note - a little over 30 GOhm dry, but drops to less than half that with just the humidity of my breath.  This will be a fun instrument to experiment with (albeit one to be careful of with the output).

[serg-el]

The MB8873H on the old board was an HD63B40 on the new one!

[DaJMasta]

There is more story behind this and more repair to be done (the HV error on unit 2), but I have them both booting properly and the eventual solution was in the manual:

To reset factory defaults, hold the auto-range key right after power on.  This fixes the Error 4 occurring after a timeout after the self tests.

I replaced the timer chip to no same effect, so I started probing.  I had a working unit, and I could swap the CPU board into the old unit and make it work, so I probed every IC pin and the ribbon connector with a scope to look for activity and type and compared them to the non-working unit.  After a somewhat exhaustive survey, I could see differences in behavior, but all the pins worked similarly.  Got to the end of my debugging this evening with everything mapped and ideas dwindling, so I turned on the working unit to check something else with the thermal camera...... and it didn't boot anymore, also with error 4.  I tried swapping CPU boards, swapping ROMs, reseating cables, everything I could think of..... then I realized - why was the SRAM being backed up?  All the calibration data is stored in non-volatile, so what was the point of the battery?

When I looked in the user manual and found the method described above, I tried it on both, and both of them reset and booted fine.


A little troubleshooting on the output generator for the one unit, but great progress after months of being stalled!  Of course it was something in software.... just some corrupted settings in SRAM from swapping chips and probing around things that it wasn't smart enough to clear on its own.  This also means the attempted replacement timer chip MB8873H is actually a valid replacement and works fine.

Oh and I made a cable like the described the user manual as the supplied test cable: Belden 9222 is rated to 1kV and if you cut one in half, stick a banana plug on the center conductor, then get a shrouded alligator clip to fit on the banana plug, you can use a regular banana jumper rated to a decent voltage with a second shrouded alligator and just zip tie them together.  Not as great shielding as if you had the guard/shield terminated in a metal end or something, but looks pretty clean and ended up being pretty cheap whereas the official accessory seems to be nowhere to be found.

[DaJMasta]

Did some reassembly and testing, my original unit had some keys that needed a few dozen actuations to start working normally, but everything else seems to be in great shape.  0.99975 +-1 LSD from 1V to 1000V on the output according to my reasonable meter, about -50fA of leakage with the output generator off, but with it powered up it centers in around +-20fA or so, so without touching anything in the frontend or any significant cleaning, it seems to be fine as well.  Measured a few things not normally measured for resistance to interesting results - a zip tie, another post it note, some wire but the insulation around it, etc.  Neat instrument!

Now some pictures:

Awful pic measuring about 30mm of a zip tie: around 6,500,000,000,000 Ohms

Also includes my "custom" cable which is a DIY copy of the original

An interesting riser board under the CPU card on the newer instrument, not sure why it needed a replacement, but runs the rear IO connector


The potted DIP-like ADC on the newer unit




And I think I found the fault on the newer unit.... spotted with the thermal camera, but a close inspection should have found it - was slightly under the black wire originally, but it looks like a contaminant between the thin trace and the wider one next to the relay (probably under the solder mask) has burned through after a while and is crossing over the board under higher voltages.  There could even be some damage on the right side near the resistor.  I'll start with cleaning and some removal of solder mask, but I wonder whether it's better to try to replace the solder mask or just bridge the traces with separate wires... in case whatever contaminant has leached into the board.

[DaJMasta]

Managed to finish the repair!  I pulled the main board (a real pain, requires removal of the transformer, high voltage shields, processor board, and then clips and screws into the base plate), milled out the damaged portion with a dremel tool, and then jumpered the two removed traces to reconnect them.  The whole high voltage section is conformally coated, and to my surprise, I think it's acrylic - trying to clean parts of it with ispropyl alcohol actually took some of it off...



Since the traces were in the high voltage section (an ADC line and a relay coil drive line), I used 1kV rated hookup wire, then applied a urethane based conformal coating on the top after cleaning it, which seemed play fine with the remaining acrylic coating.



Reassembled the whole thing, ran the self calibration routines, and started checking things out.  Voltage regulation on the output (open circuit) was basically right on, I think under 0.1% in the values I checked, leakage current centers around about 30-40fA with the generator off and an actual 0.00pA reading with the generator on.  Measuring a set of 5 soviet high value resistors (33M to 1T) at 200V, the newly fixed unit is within 0.2% of the other's reading - I don't have the calibrated equipment to confirm where exactly the reference should be, but the fact that a couple different units made several years apart, residing in different countries, and with various degrees of repairs performed can agree so closely is really impressive.

For reference,  I start seeing EMI related noise on measurements around about 1pA using my triax terminated in an alligator clip in open air test setup.  The 1T Ohm resistor measurements would vary by a few G Ohms (up to maybe 15 LSD) even when set to 4x10PLC measurements, so especially if using a low compliance voltage, measuring teraohm or above values reliably can be a chore without a shielded box.  That said, if your DUT can handle the full 1kV, you can reliably measure up to a few tens of teraohms in open air (as long as you are careful not to let the DUT or the connection cables come in contact with much of anything, I made my measurements holding the cable upright with the connectors and DUT in open air.)

A welcome addition to the bench!

[DaJMasta]

A final thing from my end, in hopefully a useful place, some printed parts for the unit:

A dust cover a three lug triax female connector
https://www.thingiverse.com/thing:4000706

A replacement foot for the R8340 (and others)
https://www.thingiverse.com/thing:4021871

[mark03]

Neat instrument.  Out of curiosity, what advantage does this have over a more common electrometer like the Keithley 617?  I see the output voltage range is 10x greater on the Advantest, but the 617 seems to have better current accuracy.

[mark03]

I wondered about the 200G max resistance on the Keithley 617 too, but then I noticed that it also has a "V/I mode" which seems to be the same as the Advantest.  Max resistance on that is claimed to be the same, ~ 10^16 ohms.

[DaJMasta]

I'm not 100% on where the 200G spec on the Keithley comes from (or the 3x10^16 spec on the R8340A, really, when I leave it open circuit it reads 10^15 or mid 10^14 ohms, so I wonder if it only applies with lowest gain modes with lots of shielding), but it seems like they are roughly equivalent: the Keithley is smaller and has more sensitive lower ranges (though measurement accuracy drops substantially, so the R8340A is actually better specified in the 200pA range), the R8340A has the higher voltage output, the better specified 200pA range, and the better overall look (highly subjective) but is larger.  Their likely is some additional remote control and operation as part of a system sorts of options, but how many people are still going to be setting up a test fixture that reads a BCD output these days?  They both still have GPIB.

Looks like prices for used units seem to agree - they're about the same.

[leighcorrigall]

I purchased an R8340 this year and it was working just fine until last week.

The first thing I noticed was that the instrument no longer could source 100 DCV (Overvoltage Detection). It is possible to do all other voltages and they are quite accurate. To my surprise, I let the instrument cool down before sourcing 100 DCV again and it worked.

It also seems to have a 'limit' when sourcing too.

There seems to be an overheating issue on my board, but I cannot seem to identify anything that appears damaged. 

Does anyone have suggestions on where to start? Did someone record the voltage taps on this thing?

[leighcorrigall]

There seems to be an overheating issue on my board, but I cannot seem to identify anything that appears damaged. 

The instrument operates without issues when I remove the cover and the shielding. It is definitely overheating. In the meantime, I have asked to borrow a friend's IR camera.

I suspect that the cause might be one of the relays (DK1a-5V, ST2-DC5V, or G6H-2-DC5) that fails in one position. From the sounds inside of the instrument, the relays correspond with the CONTACT and DISCHARGE/CHARGE/MEASURE modes.

I am going to buy a new fan (Sanyo Denki 9S0612H402‎ for 16 USD) with more flow capacity to replace the current fan (Sanyo Denki 109D0612M402) before I attempt any modifications to the mainboard.

If that doesn't work, the relays can always be purchased new from common electronics distributors. The Matsushita relay replacements would be DK1A-5V-F‎ (10 USD) and ST2-DC5V-F (14 USD). Although there are listed options on Octopart, it might be difficult to source the Omron G6H-2-DC5.

EDIT: Omron recommends the G6S Series to replace the obsolete G6H-2-DC5. G6S-2 DC5 should be the replacement and goes for 4 USD.

EDIT: The OMRON G6S-2 DC5 is half the size of the original and is incompatible!

[serg-el]

Before changing the relay and fan, try blowing on the parts with a hairdryer of the soldering station at a minimum temperature.  So you will quickly find the culprit.

[MiDi]

If it is not due to overheating it could be a cracked solder joint.

[ap]

Thermaly related issues are often caused by faulty El-caps.

[leighcorrigall]

Before changing the relay and fan, try blowing on the parts with a hairdryer of the soldering station at a minimum temperature.  So you will quickly find the culprit.

Thank you for the suggestion.

I used both a heat-shrink gun and a blow dryer without any luck. While blowing on capacitors, linear voltage regulators, or the relays, I would toggle the OPERATE button which is what usually indicated the overheating issue.

[leighcorrigall]

If it is not due to overheating it could be a cracked solder joint.

Apart from the disgusting spray-on coating that the manufactures included on the front of the board, I do not see anything that appears flawed. Maybe I am not looking in the right place. Maybe I will have to completely remove the board from the chassis, and have a look at the underside.

I will keep my eye open for anything suspicious-looking solder connections. Thanks.

[leighcorrigall]

Thermaly related issues are often caused by faulty El-caps.

The capacitors do not appear to be bulging on tops or leaking. Since they are cheap, I might as well begin there. Thank you.

On another note, I used the instrument a few days ago while examining Nicrom VRC measurements. It worked reasonably well, then all of a sudden, my DMM went to over-limit and I had to quickly shut down what I was doing. The Keithley 6500 can measure a maximum of 1000 DCV. Before shutting the R8340 down, I decided to drop the voltage to 750 DCV to see if the device was sourcing a little too much of the 1000 DCV to Keithley. At 750 DCV, the DMM still read over the limit. This is when I knew something was wrong again.