Advantest R6581 8.5 digit DMM mini teardown/repair

[Ismsanmar]

That pdf is the correct one? It's just the chapter 9 ripped from the user manual.

[gamalot]

That pdf is the correct one? It's just the chapter 9 ripped from the user manual.

Thanks for pointing this out, I didn't even notice it was just the chapter 9 of the user manual.

But that's not uncommon for Japanese companies, who like to break up technical documentation into pieces for download.

[Bobertsawesome]

Just picked up a no-power R6581T off eBay for a good price. The problem was that it had no fuse, which was quickly fixed.

I have this intermittent error printed as:

Code: [Select]

+220, "A/D check1 error"
I was hunting this down until the unit powered on with no issues. Ran internal cal and self-test and now it was working fine. Plugged up my 10v reference and it read close but off by about 300uV which is to be expected since I just ran the cal with the top off and no warm-up. Powered the unit off once or twice and again no issues. Let the unit sit off while I went to go eat and came back maybe 3 hours later to be given the same error message again as before. Supply voltages all look correct coming from the marked silkscreen at the PSU inter-board connector.

Just curious if anyone else has run into this error code before I run down a rabbit hole. Date codes on the chips seem to put this unit around the ~1997 vintage.

When running the diag procedure on boot I get weird values for the INTERNAL readout:

• x1Zero_01 : -0.02xx V
• x1Zero_02 : 2.9485xxx V
• x10Zero : 294.76xxx mV
• x100Zero : 29.47xxx mV
• 7.2Vref : 10.02929xx V
• -10Vref : -6.88504xx V
• -1Vref : -687.893xx mV
• -0.1Vref : -68.82xxx mV
• Int_temp : ~65 C - Seems correct, responded appropriately to external heating

[serg-el]

The values are incorrect. So far no one has been able to find where the problem is.
See the table of serviceable multimeters.

https://www.eevblog.com/forum/metrology/advantest-r6581-8-5-digit-dmm-mini-teardownrepair/msg3932453/#msg3932453

[Mickle T.]

+220, "A/D check1 error" means inconsistent charging and discharging timings of the integrator by standard current sources.

[Bobertsawesome]

+220, "A/D check1 error" means inconsistent charging and discharging timings of the integrator by standard current sources.

No kidding, I was just looking at that capacitor that is commonly installed reverse polarity thinking that can't be it, so I delayed fixing it. I'll report back if that fixes it along with checking those resistors.

Thanks, Mickle, your contribution to this undocumented unit has been substantial 

[Kosmic]

Does anybody understand the logic behind the 120/300V Max voltage marking on the front panel of the R6581T ?

I spent some time comparing the analog section of the R6581 and R6581T (using pictures) and they are identical. I believe the firmware is also the same.

So technically the max voltage of the R6581T should be the same as the R6581 ?

[Mickle T.]

R6581T-R6581 difference:

[Kosmic]

Interesting thank you Mickle.

My reference for the R6581 was the pictures of post #1 of this thread: https://www.eevblog.com/forum/metrology/advantest-r6581-8-5-digit-dmm-mini-teardownrepair/msg895286/#msg895286

In those pictures the R6581 doesn't have any protection over the resistor (heatshrink?) and a capacitor and resistor over the relay (like on your picture). Maybe they also changed the design of the R6581 over time ?

[Kosmic]

Mickle, I also just spotted that on your picture, the R6581 is protected by a series of 4 x 22K resistor and not 2.2K like the R6581T ?

So in the pictures of post #1 it would be a R6581T and not R6581 ? 

[leighcorrigall]

...

When running the diag procedure on boot I get weird values for the INTERNAL readout:

• x1Zero_01 : -0.02xx V
• x1Zero_02 : 2.9485xxx V
• x10Zero : 294.76xxx mV
• x100Zero : 29.47xxx mV
• 7.2Vref : 10.02929xx V
• -10Vref : -6.88504xx V
• -1Vref : -687.893xx mV
• -0.1Vref : -68.82xxx mV
• Int_temp : ~65 C - Seems correct, responded appropriately to external heating

...

Hi Bobert,

Those values are very similar to my own R6581T. Not sure how to fix them either! I have tried a lot of physical modifications/probing that you can read about above.

Perhaps you can share your EEPROM data as described by Mickle T's 'service manual.' We might identify similarities.

We will get through this.

[Mickle T.]

..., the R6581 is protected by a series of 4 x 22K resistor and not 2.2K like the R6581T ?

Yes, it's a chain of 4 blocks of 4 22k resistors in parallel. I think that this modification of the protection circuits appeared later, due to the frequent failure of devices at the time of switching the DCV range.

Since the R6581T was designed as a system voltmeter for calibrating the low-voltage analog modules of the T2000 test system, no modifications were required. Hence the voltage range of 120/300 V.

[Bobertsawesome]

..., the R6581 is protected by a series of 4 x 22K resistor and not 2.2K like the R6581T ?

Yes, it's a chain of 4 blocks of 4 22k resistors in parallel. I think that this modification of the protection circuits appeared later, due to the frequent failure of devices at the time of switching the DCV range.

Since the R6581T was designed as a system voltmeter for calibrating the low-voltage analog modules of the T2000 test system, no modifications were required. Hence the voltage range of 120/300 V.

After pulling my RT809H out of storage I was able to read and save the data from EPROM1, however, EPROM0 is either corrupted or the EEPROM itself is dead, as it was completely empty and set to 0xFF...

Edit: Yep I fried the EPROM0 wrongfully assuming it was the same type of ROM as EPROM1  . Got an ATMEL AT27C4096-55JI equivalent on the way that I will flash again from the A02 bins someone posted previously.

[Kosmic]

..., the R6581 is protected by a series of 4 x 22K resistor and not 2.2K like the R6581T ?

Yes, it's a chain of 4 blocks of 4 22k resistors in parallel. I think that this modification of the protection circuits appeared later, due to the frequent failure of devices at the time of switching the DCV range.

Since the R6581T was designed as a system voltmeter for calibrating the low-voltage analog modules of the T2000 test system, no modifications were required. Hence the voltage range of 120/300 V.

Thank you for the information. It might be interesting documenting that modification. I for one, would be interested to implement it on my R6581T.

Your help is always appreciated Mickle, thank you 

[dietert1]

Input protection by power resistors is a bit oldfalshioned. One possible mod is an active current limiter with two back-to-back HV mosfets, that can block 1000 V at a small current, like 5 mA (equivalent to 200 KOhm). Under normal operating conditions, its resistance will be 100 or 200 Ohms, so the mod can also reduce noise.
A schematic can be found in Kleinsteins DIY multimeter thread.

Regards, Dieter

[Mickle T.]

Even the top-end Fluke 8508A uses the classic 3x 5kOhm resistor chain protection without any significant performance degradation.

[dietert1]

At 1 KV that makes 1000 V x 1000 V / 15000 Ohm = 66 W of heat. Bad. Probably they avoid that by using some input relay or mosfet switch. Or they spec a lower limit, similar to 6581T

Regards, Dieter

[Kosmic]

Or they spec a lower limit, similar to 6581T

From what I was able to gather, looking at different pictures, the R6581T input is similar to original R6581. As Mickle mentioned, probably because of high failure rate  , they decided to do a fix and switch the resistors and added some protection on the relay (K008). Now since this is a manual fix they don't bother doing that on the R6581T.

So technically, the R6581T should be able to support 1Kv at least as good as the original R6581. That being said I would personally play safe and avoid autoranging with high voltage.

[Kleinstein]

The protection with relatively low resistors (like 15K) only works in combination with a realy to turn off the input once overload is detected. A problem here is that most of the shelf relays are not rated to turn off some 1000 V with close to 100 mA of current flow. So there is a chance to get a damage from the arc not stopping when turning off the relay.
Another problem is that to turn off reliably one would essentially use a NO contact and thus have the relay coild powered under normal operation and this causes heat that can cause an thermal EMF error. The choice of a suitable relay is far from easy.

A slight step up could be the use of a PTC as part of the resistor chain, so that even if the relay fails to open the resistors would not overheat too much, at least reducing the damage.

The use of active elements like MOSFETs (depl. mode or with photovoltaic drive) is also not without a problem: the maximum voltage is limted (rarely much above 1000 V) and they tend to fail short, if they fail. That type of protection is used with some Keithley meters (2000, 2001,2002). Ideally it would also be combined with some secondary protection like a PTC / fusible resistor.

From what I was able to gather, looking at different pictures, the R6581T input is similar to original R6581. As Mickle mentioned, probably because of high failure rate  , they decided to do a fix and switch the resistors and added some protection on the relay (K008). Now since this is a manual fix they don't bother doing that on the R6581T.

So technically, the R6581T should be able to support 1Kv at least as good as the original R6581. That being said I would personally play safe and avoid autoranging with high voltage.

I would more like consider the 1 kV rating for the early R6581 to be a dubious. So better don't use them for high voltage.

[Kosmic]

From what I was able to gather, looking at different pictures, the R6581T input is similar to original R6581. As Mickle mentioned, probably because of high failure rate  , they decided to do a fix and switch the resistors and added some protection on the relay (K008). Now since this is a manual fix they don't bother doing that on the R6581T.

So technically, the R6581T should be able to support 1Kv at least as good as the original R6581. That being said I would personally play safe and avoid autoranging with high voltage.

I would more like consider the 1 kV rating for the early R6581 to be a dubious. So better don't use them for high voltage.

On the 100 and 1KV range, the signal goes through the HV divider so no problem there. As you described the problem is related to switching and the improvement were located on K008 and R008 - R0011.



P.S: Thanks Mickle for the schematic, this is awesome 

[Bobertsawesome]

...

When running the diag procedure on boot I get weird values for the INTERNAL readout:

• x1Zero_01 : -0.02xx V
• x1Zero_02 : 2.9485xxx V
• x10Zero : 294.76xxx mV
• x100Zero : 29.47xxx mV
• 7.2Vref : 10.02929xx V
• -10Vref : -6.88504xx V
• -1Vref : -687.893xx mV
• -0.1Vref : -68.82xxx mV
• Int_temp : ~65 C - Seems correct, responded appropriately to external heating

...

Hi Bobert,

Those values are very similar to my own R6581T. Not sure how to fix them either! I have tried a lot of physical modifications/probing that you can read about above.

Perhaps you can share your EEPROM data as described by Mickle T's 'service manual.' We might identify similarities.

We will get through this.

Hi Leigh,

Just want to confirm if your DMM is making it past the self-check? I intend on ordering a JBC tweezer station that I have been putting off until I really needed it, and I think now is the time. If all else fails, I will do some sweeping replacements of passive components in the ADC section.

I got some replacement ROMs to reprogram my self-induced failure of EPROM0 before continuing with measurements.

[Ugur]

Hello ,
I haven't read all the correspondence, but there's a long talk here.
I need support with Fluke 8508A, can you give me some ideas?
The device gives error 9005.4 In guard error line, it also gives a lot of error in Ohm, DCV and other steps. But the device did not give an error when it warmed up.
I fixed this error caused by the A4 card, now everything is fine and the self test is completed without any problems.
When I want to do a adjustment calibration for ACV, I get the below error message during 100mV 60 Khz calibration. (AC 200mV range)
Can you comment on this topic?
ERROR DURING HFTRIM CAL - 2003

[Mickle T.]

Advantest R6581 and Fluke 8508A are very different beasts.

HFTRIM CAL 2003 error is listed in Datron 1281 Service Manual.

[little.tesla]

To improve the TC of the meter a so called copper mod around R234 is mentioned. To my understanding this mod involves to cut a leg of R234 and to insert in series a resistor made out of copper wire. Does anybody have any further details about this mod?

[branadic]

Download this package:

http://www.ko4bb.com/getsimple/index.php?id=download&file=Advantest/Advantest_R6581_Multimeter_Service_Manual_Schematics.rar

You will find images in the folder Modding\TC fix

-branadic-