Author Topic: Advantest R8340A Picoammeter, High resistance meter review  (Read 29227 times)

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Offline PartialDischargeTopic starter

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Advantest R8340A Picoammeter, High resistance meter review
« on: March 10, 2017, 04:58:30 pm »
Recently I purchased a few units of this equipment. It is fairly unknown and there's not a single reference to it in this forum. It is also complex at first and I'm gradually learning more about it with the users manual ( http://exodus.poly.edu/~kurt/manuals/manuals/Other/ADV%20R8340,%20R8340A%20Operation.pdf )




Although it is branded as an "Ultra High Resistance Meter" it is 3 equipments in one:

-voltage source/sink, up to 1000V
-Resistance meter, up to 30.000.000 Gohms
-current meter, down to 10fA of resolution.

A few specs:






Output accuracy of the voltage source is quite good:




Both the measurement unit and the voltage source are fiber optic isolated and this allow to float the inputs up to 1100V. The input jacks can be configured to work in different configurations,explained in the manual, with or without the voltage source. Input connector is triax:




To be continued....
« Last Edit: March 12, 2017, 08:58:10 am by MasterTech »
 
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Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #1 on: March 10, 2017, 05:15:19 pm »
 At the back of the unit there is the gpib, D/A output, BCD output of the data and trigger signal,



Unfortunately this ones are configured for 110VAC so I'm currently using a stepdown transformer. On the inside there are configuration jumpers but I still haven't had time to figure out how to set it for 230:



The inside is populated with 3 boards a linear power supply and a aluminum shield. Inside there is still another metal cover for the input I-V amplifier:





An LMC6081 , Ibias of 10fA, can be seen in the beautifully constructed IV converter. It has a ink white dot over it, so maybe it is a selected part. This is the topology according to the manual:




A 12bit DAC can also be seen next to precision resistors:




Depending on your own interests this unit may be useful or not, but I'm usually interested in measuring leakage currents of certain devices and thats why I bough these units. For example this is the current flowing across a 550V TVS when 100V is applied:



Measurement of a 100G resistor:



« Last Edit: March 10, 2017, 06:44:00 pm by MasterTech »
 
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Offline Vgkid

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #2 on: March 10, 2017, 07:24:51 pm »
Thanks for tearing it down, I always liked seeing the internals of Advantest gear.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #3 on: March 11, 2017, 01:13:02 pm »
The gain of the I-V transimpedance amp can make a difference on the measure and it needs to be adjusted according to ones objectives. The manual gives some ideas,




I took a 0.01% 1M resistor and applied 1V to it, with a gain of x10000 noise becomes worst but it can be offset with a higher integration time:







This unit seems to be oriented for testing in production lines. Among other features it has some programs that automate the execution of the measurement, voltage source discharge (in case there is a capacitance at the output), charge, measurement, and discharge. It has 6 programs and the times/delays are selectable. This is one of the programs:


« Last Edit: March 11, 2017, 01:22:31 pm by MasterTech »
 
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Offline razberik

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #4 on: March 11, 2017, 03:30:18 pm »
Perfect ! Do you have some manual ? Any schematic available ?
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #5 on: March 11, 2017, 03:32:34 pm »
Perfect ! Do you have some manual ? Any schematic available ?
Manual is linked in the OP... schematics I've searched but no luck
 

Offline razberik

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #6 on: March 11, 2017, 03:40:23 pm »
schematics I've searched but no luck
Be like me :D : https://www.eevblog.com/forum/testgear/keithley-64856487-teardown/msg1126821/#msg1126821
Reverse the schematic ! At least, the input block seems to be very simple. Tho most important part are values of resistor+FB capacitors and relay wiring diagram. I can see something from photo, but I am unable to read values of resistors.
 

Offline ocw

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #7 on: March 12, 2017, 02:11:00 am »
For resistance and current measurement of voltage dependent currents in at least the x1 and x10 amplifier setting modes, the 2 - 3.6 volt drop (for x1) for full scale readings will hurt the current measurement accuracy of low voltage currents.  Similarly, for resistance measurement, that's why the specification sheet accuracy is for 100+ volts in the x10 and above modes.
 
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Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #8 on: March 12, 2017, 08:59:56 am »
Perfect ! Do you have some manual ? Any schematic available ?
Manual is linked in the OP... schematics I've searched but no luck
just realized the link to the manual in the OP was wrong: :-\
http://exodus.poly.edu/~kurt/manuals/manuals/Other/ADV%20R8340,%20R8340A%20Operation.pdf
 

Offline cncjerry

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #9 on: March 19, 2017, 07:18:06 pm »
So they are like an electrometer I guess.  Are they able to source current or just voltage?  My Keithley electrometer can be used to source current in the resistance ranges.  You have to be careful with them because they can give you a scare-shock that can cause a nice elbow bang on the old "not so funny bone" which is always worse than the shock.
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #10 on: March 20, 2017, 06:07:16 am »
So they are like an electrometer I guess.  Are they able to source current or just voltage?  My Keithley electrometer can be used to source current in the resistance ranges.  You have to be careful with them because they can give you a scare-shock that can cause a nice elbow bang on the old "not so funny bone" which is always worse than the shock.
This one sources voltage. I'd wish it had a function for sweeps but that could be done with gpib. Pretty happy with this instrument, before it I had no way to explore >100Mohm resistors and the sub micro-amp world.
 

Offline Justincase1979

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #11 on: November 14, 2017, 06:21:29 pm »
Hi. Does it look like it is possible to change the line voltage of the meter in a simple way?
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #12 on: November 14, 2017, 07:54:55 pm »
Yep, I already changed them
 

Offline Justincase1979

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #13 on: November 14, 2017, 08:27:09 pm »
Ok, so just a switch?
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #14 on: November 15, 2017, 06:27:46 am »
Not that easy. See the picture I uploaded as “voltage slection”? there are a set of wire jumpers, the space is tight and not easy to change them. If you are interested I can upload a picture of the new configuration for 240
 

Offline Pipelie

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #15 on: December 14, 2017, 02:01:40 am »
Yep, I already changed them. check the photo below. :)
« Last Edit: December 14, 2017, 02:03:24 am by Pipelie »
 
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Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #16 on: October 12, 2018, 05:49:16 am »
Just picked up one of these meters broken for pretty cheap, trying to get it running and wondering if another user had a copy of the digital board's program ROM.  The display started garbled and the voltage was set to its lowest (putting 14V on the input of the LM317 powering the 5V rail!)  I swapped the jumpers to be 120V friendlier (only 11V now, that handwritten note was quite useful!), then swapped the socketed 74ALS245 for a replacement an HCT, but operating frequency is only 2MHz) because I was seeing runt pulses on the RAM data lines.  Still seeing the runt pulses, but now the front panel reads Err LR on boot - which is a logic ROM fault.

If anyone has an R8340A with a good ROM they can copy, I would be very much appreciated.  The handwitten code on the window cover for the UV EPROM reads "002672 B01".
« Last Edit: October 12, 2018, 05:51:17 am by DaJMasta »
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #17 on: October 12, 2018, 06:24:17 am »
I can do that no problem, will do it this weekend. The lack of schematics in this meter is really frustrating. I had a couple with weird things displayed and I'm sure its an easy repair from the logic side but with no schematics...
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #18 on: October 12, 2018, 07:27:09 am »
That would be very appreciated!  I've got a programmer and a couple SST27SF512 on the way as a replacement - hoping I can go with a newer flash based EEPROM replacement instead of the older UV stuff, and the pinout and configuration seem to match.  Since the chip can still get runt pulses out, so long as the programmer is high enough impedance and is driven fairly slow, I may actually be able to salvage the data on the ROM, but even if I can extract it, there's no guarantee it will be good and I haven't used the programmer that's on its way.


It seems basically all Advantest gear is very closed... and the little technical servicing information available is often in Japanese.  Makes it difficult, but stuff is generally well laid out and labeled, but sometimes it's very tightly packed together.  The RF gear in particular I tend to pull off the chassis cover and just find a whole new chassis worth of plates holding in and shielding various assemblies, can take quite a while to figure out how to even disassemble.  This instrument and its little brother, the R8240 seem to be very tough to find info on outside of some catalogs that don't even list them as made by Advantest.


I've only looked in depth at the logic board under the BCD output board, but aside from one chip, it's not too bad to get an idea about.  The one I couldn't find data on was the MB8873H, but from the connections and the limitations of the micro, I think it's an address expander or some kind of memory controller - data lines from the RAM and ROM at least connect to it and the MCU seems to only have 64k worth of address capability built in, even though the ROM alone is that big.
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #19 on: October 14, 2018, 04:20:06 pm »
Here it is. I have version 2_53 though. But HW is probably compatible, give it a try
« Last Edit: October 16, 2018, 05:31:40 am by MasterTech »
 
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Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #20 on: October 15, 2018, 06:20:14 pm »
The ROM file shows up as 0kB and is an empty zip file when downloaded, I think something went wrong?

I've gotten the programmer and even overdriving the Vcc for the ROM I can't get the checksum to match on two consecutive reads.  I made 15 copies at various settings and saved them, but I doubt any will be an uncorrupted image.  The fairly inexpensive programmer I have probably doesn't support lowering the high threshold voltage low enough to catch the runt pulses consistently, but I'll experiment a bit more as I wait for the replacement chips to arrive.
 

Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #21 on: October 15, 2018, 09:40:56 pm »
 MB8873H  -> PTM (programmable timer)
Отсюда:
https://patents.google.com/patent/US5541860
« Last Edit: October 15, 2018, 10:09:57 pm by serg-el »
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #22 on: October 16, 2018, 05:37:33 am »
The ROM file shows up as 0kB and is an empty zip file when downloaded, I think something went wrong?
reuploaded, dunno what happened

Quote
I've gotten the programmer and even overdriving the Vcc for the ROM I can't get the checksum to match on two consecutive reads.  I made 15 copies at various settings and saved them, but I doubt any will be an uncorrupted image.  The fairly inexpensive programmer I have probably doesn't support lowering the high threshold voltage low enough to catch the runt pulses consistently, but I'll experiment a bit more as I wait for the replacement chips to arrive.

Same thing happened to me when I was reading mines, I was using Virtualbox to run the reader program (mine is Elnec), cause all I have is macs. I switched to the same program in another computer but this time using VMware and it was fine. No idea what happened there.
 

Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #23 on: October 16, 2018, 07:21:38 am »
R8340 ROM dump firmware
А также фото и мануалы.  ;)
https://drive.google.com/open?id=0B6_s05G2HpcwRnhiZ3NVR2RTQkk
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #24 on: October 16, 2018, 10:59:01 am »
I believe the R8340 has SW version 2-01 and R8340A has 2-53
« Last Edit: October 16, 2018, 12:19:01 pm by MasterTech »
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #25 on: October 16, 2018, 03:42:53 pm »
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.
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #26 on: October 22, 2018, 03:08:01 am »
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.
 
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Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #27 on: October 22, 2018, 04:13:27 am »
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.
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #28 on: October 31, 2018, 05:49:23 am »
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.
« Last Edit: October 31, 2018, 05:51:11 am by DaJMasta »
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #29 on: October 31, 2018, 04:54:58 pm »
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.
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #30 on: November 01, 2018, 05:56:08 am »
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.
 

Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #31 on: November 01, 2018, 06:42:21 am »
Check the power and processor board
« Last Edit: November 02, 2018, 03:43:02 pm by serg-el »
 
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #32 on: November 05, 2018, 02:43:46 pm »
Check three consecutive resistors. Burn often.
 
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Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #33 on: September 25, 2019, 06:17:47 am »
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).
 

Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #34 on: September 26, 2019, 11:58:02 am »
The MB8873H on the old board was an HD63B40 on the new one!
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #35 on: October 12, 2019, 05:44:29 am »
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.
 
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Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #36 on: October 13, 2019, 05:51:53 am »
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.
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #37 on: November 23, 2019, 04:12:24 am »
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!
« Last Edit: November 23, 2019, 04:14:08 am by DaJMasta »
 
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Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #38 on: December 04, 2019, 08:52:07 pm »
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
 
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Offline mark03

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #39 on: December 05, 2019, 04:16:48 am »
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.
 

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #40 on: December 05, 2019, 02:06:15 pm »
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.
 

Offline DaJMasta

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #41 on: December 05, 2019, 04:06:58 pm »
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.
 

Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #42 on: March 12, 2021, 02:57:55 pm »
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?
« Last Edit: March 12, 2021, 03:04:54 pm by leighcorrigall »
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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #43 on: March 14, 2021, 02:20:33 am »
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!
« Last Edit: April 14, 2021, 02:51:41 pm by leighcorrigall »
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #44 on: March 14, 2021, 07:14:37 am »
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.
 
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Offline MiDi

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #45 on: March 14, 2021, 09:17:26 am »
If it is not due to overheating it could be a cracked solder joint.
 
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Offline ap

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #46 on: March 14, 2021, 09:29:35 am »
Thermaly related issues are often caused by faulty El-caps.
Metrology and test gear and other stuff: www.ab-precision.com
 
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #47 on: March 17, 2021, 02:13:26 pm »
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.

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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #48 on: March 17, 2021, 02:20:46 pm »
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.
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #49 on: March 17, 2021, 02:27:43 pm »
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.
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Offline Kleinstein

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #50 on: March 17, 2021, 03:01:27 pm »
Too high a output voltage could be from something like broken (fused) transistors in a linear regulator stage. One can usually check the transistors in circuit  (look for a short).
 

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #51 on: March 24, 2021, 01:10:03 am »
Apologies, I haven't had much time this month to work on this problem.  :horse:

My friend lent me his old FLIR thermal camera (emissivity was set to 0.95). Attached are some comparison photos of my Advantest R8340 after a warmup of 1 hour with an open case. I hope this is useful for some people.

Cheers.

EDIT: FYI, this Advantest has issues with the linear voltage regulators. I will consider performing another IR analysis to compare with this one.
« Last Edit: April 09, 2021, 12:29:44 pm by leighcorrigall »
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #52 on: April 08, 2021, 01:30:05 pm »
Check three consecutive resistors. Burn often.

Hi serg-el,

I am making a list of replacement components for the R8340A and would like to know what you used (or anyone else for that matter) as replacements for these resistors. Please advise.

Thank you.
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #53 on: April 08, 2021, 04:59:15 pm »
There are the most common resistors.  Since they work in heavy duty, the soldering needs to be updated.  Desolder, re-tin and solder back.  If you change to new ones - solder with a gap from the board for better cooling.
 
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #54 on: April 09, 2021, 02:15:46 am »
There are the most common resistors.

Any idea what the current/voltage/power would be? I am too afraid to probe the active board as it has already shown signs of overvoltage.

The 4-band colours are not clear, so I think I will have to desolder each one to confirm their tolerances before ordering...  :palm:

I was thinking of replacing the generic resistors with these Vishay types:
https://www.mouser.ca/datasheet/2/427/vr25vr37vr68-1762017.pdf
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #55 on: April 14, 2021, 07:53:04 pm »
Too high a output voltage could be from something like broken (fused) transistors in a linear regulator stage. One can usually check the transistors in circuit  (look for a short).

You are correct. I found a faulty linear regulator at U50 with markings NEC 7915 and replaced it with an LM7915CT/NOPB.

The following linear regulators were identified while examining the board and have all been replaced.

EDIT: Sorry for the upside-down picture... Windows displays it upright but when they are uploaded they become reversed.  :palm:

1211163-01211169-1
« Last Edit: April 14, 2021, 08:38:36 pm by leighcorrigall »
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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #56 on: April 14, 2021, 08:02:26 pm »
Thermaly related issues are often caused by faulty El-caps.

All electrolytic capacitors have been replaced with the exception of C113 and C114 because I cannot find suitable replacements. The removed components that I was able to test seemed to be operating within tolerance.


« Last Edit: April 14, 2021, 08:39:46 pm by leighcorrigall »
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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #57 on: April 14, 2021, 08:13:57 pm »
The 4-band colours are not clear, so I think I will have to desolder each one to confirm their tolerances before ordering...  :palm:

I have itemized the following resistors after desoldering them from the board and measuring them. They will be replaced with higher quality equivalents of greater performance. 1211165-0

R188 to R192 R156 to R159 were operating at ~ 180 °C which damaged the mainboard and caused the silicone coating on the bottom-side to vaporize over time. 1211167-1
« Last Edit: April 21, 2021, 01:53:05 pm by leighcorrigall »
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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #58 on: April 14, 2021, 08:35:43 pm »
Does anyone have recommendations for the following components (pictured and itemized)? I have not been able to properly source these components yet. :-\

I plan on replacing them all just to be certain. There are some signs of thermal damage on the backside of the board that I am concerned about.

Thanks.

EDIT: Sorry for the upside-down picture... Windows displays it upright but when they are uploaded they become reversed.  :palm:
« Last Edit: April 14, 2021, 08:41:27 pm by leighcorrigall »
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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #59 on: April 21, 2021, 12:02:41 am »
I used acetone to remove portions of the protective layer on the mainboard so that I could replace critical components such as resistors.
1213252-01213254-11213256-21213258-31213260-41213262-5

A list of resistor candidates is attached. Yellow indicates the component selected and installed onto the mainboard.
1213264-6

The coating might be silicone. Does anyone suggest recoating the board before testing? If so, what product would you recommend?

I also replaced the linear voltage regulators pictured below. Just now I realized that the aluminum support bracket may have been electrically insulated from the regulators with a plastic film and an insulated washer on the screw. At the time, I thought it would be better for heat dissipation to discard the plastic film, but now I am debating whether or not to include it again. Does anyone know why the design has implemented this feature?
1213266-7

Thanks.
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Offline dietert1

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #60 on: April 21, 2021, 05:55:56 am »
You cannot mount a 79xx regulator and a 78xx regulator onto the same heatsink without insulating one of them. This is because the thermal pad of the positive regulator is Gnd and for the negative regulator it is Input. In your case, if you insulate the 7915 once more, it should work. The heatsink will then be grounded by the two positive regulators. If this isn't desirable, you also need to insulate the positive regulators once more. Then you can connect the heatsink as guard, for example.

Regards, Dieter
 
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #61 on: April 21, 2021, 06:06:29 am »
Since the radiator is screwed onto the housing, the regulators must be insulated.  Otherwise, an unnecessary ground loop may occur.  It is possible to use insulated flange regulators, but they have higher thermal resistance, so this is not the best option.  Resistors R156 ... 159 are best mounted horizontally.  It is possible at different heights from the board.  Cool down better.  The insulating tubes on them must be pulled to the very body of the resistor.
 

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #62 on: April 21, 2021, 01:43:48 pm »
... then applied a urethane-based conformal coating on the top after cleaning it, which seemed to play fine with the remaining acrylic coating.

Can you let me know what urethane coating product that you used? I am at the stage where I need to reapply a coating.

Thanks!
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #63 on: April 21, 2021, 02:23:07 pm »
You cannot mount a 79xx regulator and a 78xx regulator onto the same heatsink without insulating one of them. This is because the thermal pad of the positive regulator is Gnd and for the negative regulator it is Input. In your case, if you insulate the 7915 once more, it should work. The heatsink will then be grounded by the two positive regulators. If this isn't desirable, you also need to insulate the positive regulators once more. Then you can connect the heatsink as guard, for example.

Regards, Dieter

Since the radiator is screwed onto the housing, the regulators must be insulated.  Otherwise, an unnecessary ground loop may occur.  It is possible to use insulated flange regulators, but they have higher thermal resistance, so this is not the best option.

These are two great reasons. I originally decided that the plastic insulators were to prevent ground looping, as sergi-el pointed out. At the back of my mind, when performing part sourcing, I did notice that the 78XX and 79XX series regulators were oppositely polarised. I wonder why Advantest decided to go with this design.

Attached are some pictures of the refurbishing process. Thermal paste was used to ensure good conduction through the materials. The excess paste was removed to prevent shorting. The high-voltage assembly was not provided thermal paste directly on the backside of the regulators as not to compromise the yellow insulation pad.
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #64 on: April 21, 2021, 08:21:48 pm »
Resistors R156 ... 159 are best mounted horizontally.  It is possible at different heights from the board.  Cooldown better.  The insulating tubes on them must be pulled to the very body of the resistor.

The instrument has been running for more than 2 hours without experiencing the problems that I mentioned previously. Before installing the shield and cover of the enclosure, I measured R156 to R159 (OHMITE MOX5002703GSE, 4 x 270 kΩ, 2 W/resistor, 100 ppm/°C, 155 °C max operating temperature) with an IR camera. The temperatures were measured at the base of each resistor. 75 °C was measured at R159, 85 °C was an average value and the maximum temperature was found to be 105 °C at R156. This is almost half the temperature that was observed previously when inspecting the original generic resistors. If one can source a high-voltage resistor of equal or greater power, then this setup should work fine. Your suggestion of positioning the resistors horizontally would improve thermal dissipation, but I wanted to avoid crowding the resistors and inhibiting airflow which also must be considered. Overcrowding is a problem with this Advantest design. Note that I applied your horizontal suggestion for most of the other power resistors.

Another alternative is to further divide the heat load amongst additional resistors , but this might get complicated. Otherwise, if the OHMITE MOX (2 Watt) or Vishay VR68 (1 Watt) resistors are unsuitable, then one can try and contact Japan Fine Chemicals https://www.jfine.co.jp/eng/e_c/resistors/lead/. These resistors were already incorporated in the original Advantest R8340 design and are rated for the kV range.

---

Surprisingly, all the taps that I measured previously have similar voltages to what was measured presently. If anyone has measured the voltages at these positions, I would appreciate it if you would share them for comparison.


At this point, I am assuming that the instrument is working properly and the overheating issues that were experienced previously have been dealt with. My guess is that the problem originated from the R156 tp R159 resistors operating at 185 °C and a linear regulator located at U50 that was showing signs of failure.

Eventually, I am going to have to recoat the board with some protective layer. As I have never seen coatings like this on circuit boards before, I would also appreciate it if someone with experience could provide a recommendation on a product that they have used.

Thank you all for your help and comments.  :-+
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #65 on: April 21, 2021, 09:20:50 pm »
Apparently your transformer is switched to 220V.  The modern standard for mains voltage is 240V.  Switch the transformer to 240V.  This will reduce the voltage at the unregulated outputs, and lower the temperature of the stabilizer microcircuits.
« Last Edit: April 21, 2021, 09:33:34 pm by serg-el »
 

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #66 on: April 21, 2021, 09:41:52 pm »
Apparently, your transformer is switched to 220V.  The modern standard for mains voltage is 240V.  Switch the transformer to 240V.  This will reduce the voltage at the unregulated outputs, and lower the temperature of the stabilizer microcircuits.

The instrument labels claim to be configured for 90 - 110 VAC. My home operates at 117.2 VAC. When you suggest that I 'switch the transformer to 240 V', will I find a switch inside the transformer shielded box? Keep in mind that I am a beginner.  :o
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #67 on: April 21, 2021, 09:53:08 pm »
Clear.  So your transformer is configured for 100V.  Switch it to 120V.
« Last Edit: April 21, 2021, 10:01:28 pm by serg-el »
 
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #68 on: April 22, 2021, 01:36:48 am »
Clear.  So your transformer is configured for 100V.  Switch it to 120V.

Big thank you, serg-el. :clap:

These are the kind of problems I would not have thought about myself because I only began learning about electrical engineering last summer. I am so fortunate to be able to learn from you and other members of this forum.

The average voltage of the unregulated taps has dropped 26 %. This will definitely prolong the life of the instrument!  :-+


The maximum temperature of the R156 to R159 is now 85 °C from 105 °C, a reduction of 19 %.   ;D


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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #69 on: April 25, 2021, 07:36:10 pm »
What a nightmare... Not only did this instrument destroy my Keithley DMM6500's OHM and DCI modes for no apparent reason when I was operating in DCV mode, but it also continues to show the same error message as before.

I left the instrument on standby to determine whether the error would return for a few days after the repair. Interestingly, the Advantest R8340 seems to be in the same calibration from pre-repair. I guess the power resistors and capacitors have little to do with the precision.

Yesterday, I received the same message "Overvoltage Detection Message" from Section 3-6 (page 36) when I set the instrument to source 100 DCV.  I wonder why the instrument is reporting that an external voltage is interfering with the instrument.  Could the instrument be shorting somewhere? When the error occurs, the instrument squeaks and then returns to standby. I can set the instrument to any value, but 100 DCV. Nothing is connected. The GUARD, GROUND, and LO are connected by the short bars. If I leave the instrument OFF for a while and come back to it, the error goes away again.

Does anyone notice that the high-voltage light flashes when the instrument is turned ON, and when switching from DISCHARGE, CHARGE, and MEASURE?

Figure 10 - 1 (page 267) indicates that there is a dedicated amplifier for the 100 DCV range. Maybe I have to start there.

I am so lost and frustrated.  :'(

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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #70 on: April 26, 2021, 02:52:02 pm »
...

Inside there is still another metal cover for the input I-V amplifier:

...



An LMC6081, Ibias of 10fA, can be seen in the beautifully constructed IV converter. It has an ink white dot over it, so maybe it is a selected part. This is the topology according to the manual:



...


There are some differences between the R8340 (bottom) and R8340A (top) in the shielded interface section of the board:

U1 - NEC C252A
R15 - COPAL 20kΩ 50E K-9W
R16
C7
C?
D2
D3
« Last Edit: April 26, 2021, 02:54:04 pm by leighcorrigall »
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #71 on: April 26, 2021, 03:00:06 pm »
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.

This seems to be a bad spot. I am going to add some solder here.


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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #72 on: April 26, 2021, 04:48:14 pm »
Attached are two separate characterizations of the R8340 high-voltage source at 1000 DCV at 0.0005 NPLC and 10 NPLC. The instrument does not overshoot, is surprisingly stable and repeatable.
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #73 on: April 26, 2021, 07:16:04 pm »
My Advantest R8340 seems to overshoot consistently on the maximum output of the 10.003 to 100.00 DCV range. The instrument might be experiencing 'overvoltage' due to this characteristic. When the instrument becomes too hot, the temperature coefficient of a component changes just enough to through the overshoot value above the 'overvoltage detection' limit. The overvoltage is well beyond the 'generation accuracy', outlined in the datasheet.
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #74 on: April 29, 2021, 12:35:23 pm »
I think I figured it out. The last owner had replaced the fan and must have reversed the fan direction in the process.  :horse:

Can anyone confirm that the fan should blow outwards? If pointed inwards, the stagnant air eventually warms up enough to cause some components to misbehave. The instrument has been running smoothly for several days now and I have not been able to repeat the problem.
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Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #75 on: April 29, 2021, 01:27:18 pm »
In my units the fan blows outwards
 
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Offline leighcorrigall

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #76 on: May 04, 2021, 11:24:14 pm »
Eventually, I am going to have to recoat the board with some protective layer. As I have never seen coatings like this on circuit boards before, I would also appreciate it if someone with experience could provide a recommendation on a product that they have used.

I purchased a clear insulating varnish called "EL 600" manufactured by Sprayon https://www.sprayon.com/product/el600-clear-insulating-varnish/. According to McMaster-Carr https://www.mcmaster.com/7437K21/ and the information printed on the can, the coating has a dielectric strength of up to 2300 volts per mil and an operating temperature of 150 °C (I will assume that maximum temperature comes from the ASTM D115 specification). To apply the coating, I will have to remove the board again and take it outside. I will share my results with anyone that is interested.  :horse:
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Offline Kleinstein

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #77 on: May 05, 2021, 08:19:35 am »
This spray varnish likely contains quite some solvents. So one should be careful with some film capacitors: they may get damaged from solvent. Especiall PS type caps are quite sensitive to solvents and could be damaged.
 
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Offline BD1QMP

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« Last Edit: December 20, 2023, 01:54:39 pm by BD1QMP »
 
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Offline serg-el

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #79 on: December 20, 2023, 04:40:22 pm »
 
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Online Kosmic

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #80 on: January 24, 2024, 02:57:01 am »
I disassembled my R8340 for clean-up and did not notice where the white cable from the transformer was going exactly. Now i'm reassembling and i'm not sure where it should be fixed.

Is it the guard and should be screwed with the shield standoff ? anybody know ?

« Last Edit: January 24, 2024, 03:54:57 am by Kosmic »
 

Online Kosmic

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #81 on: January 24, 2024, 04:37:49 am »
I found my answer looking at some pictures from serg-el.


 

Offline BD1QMP

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #82 on: May 05, 2024, 01:41:38 pm »
Today, My 8340A was broken  :(. the reason is when I output 1000V, it is short with ground. the main fuse was broken, when I replace the fuse, it give out Err HV kV.   it can output 1~100V.   cannot output >100V.

No I have to repaire it :( :( :( :( :( :( :( :(
     
 

Offline BD1QMP

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #83 on: May 06, 2024, 02:41:01 pm »
1 days later, I turn on it for a while, 0-100V is fine.
but when I setup the source output to 101V, the V source output voltage is 1050V. there should be some mosfet/transistor broken.
when I remove the cover, I found Q55(C3150. NPN, 800V) and Q56(K786 N-Mos,900V) are very hot.
 
Today, My 8340A was broken  :(. the reason is when I output 1000V, it is short with ground. the main fuse was broken, when I replace the fuse, it give out Err HV kV.   it can output 1~100V.   cannot output >100V.

No I have to repaire it :( :( :( :( :( :( :( :(
   
 

Offline BD1QMP

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #84 on: May 11, 2024, 12:32:20 pm »
I found Q60 (Mosfet K786)is broken, after replace it with a used K786 (bought from Taobao, 0.8RMB/unit), the HV output can reach 400V, but beyond 400V setup is output 400V. 
 

Offline PartialDischargeTopic starter

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Re: Advantest R8340A Picoammeter, High resistance meter review
« Reply #85 on: May 11, 2024, 12:43:07 pm »
Check the resistors that are varnish coated, they may be bad/burnt
 


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