Solartron 7061 7.5 Digits Multimeter Teardown and Repair  - Page 1
Forum section: electronics / repair

author: Kosmic
author_rank: Super Contributor
timestamp: January 13, 2019, 02:53:20 am
content: Some time ago, I had the opportunity of buying 2 Solartron 7061 7.5 Digit Multimeter. They were sold for parts and only tested for power-up only.The Devices:The Solartron 7061 was sold in late 80's as a fast and accurate (7.5 digits) multimeter. It can capture 1500 readings per seconds, got an interesting set of math functions and has some scanning capabilities (with the second input or an extension card).Both of the units I bought were built in 1988 and are equipped with the revised PCB 13 & 15.The Problems:Unit #1:- Failing 0V Test.- A little bit unstable. At 6.5 digits the 2 last digits are jumping quite a bit.- VDC is off (the only thing tested).Unit #2:- Pass selftest.- Readings are erratic. Ex, if 10V is applied at the input, readings will somehow increase but never reach 10V. If the input is shorted, readings will go down but never reach 0V.

author: Kosmic
author_rank: Super Contributor
timestamp: January 25, 2019, 02:19:36 am
content: Unit #1:I decided to investigate the test failure first. The manual of the 7061 do not mention anything specific about the "0V Test Fail" error message. Nevertheless, a quick search on the web revealed some information hidden in the manual of the Solartron 7081 (big brother of the 7061). They recommend investigating IC201 in the integrator. Since the integrator of the 7081 and 7061 are similar this was a really good lead.The Integrator:The role of the integrator is to merge the forcing wave and input signal together and present a ramp up/down to the comparator. The comparator then generate 2 pulse trains, called +Glug and -Glug. Those pulse trains are then simply counted and digitalized. The technique used is similar to the Delta Sigma modulation used in many modern analog to digital converter IC.After I quick inspection I realized that someone already tried to repair the instrument. IC202 has been socketed (normally only IC201 and 203 are on socket) and the LM301 that was supposed to be there has been replaced by a RAYJM38510. I quickly replaced the RAYJM38510 by a new and working LM301 but the 0V test was still failing.A quick scan of the manual revealed the different test points of interest in the integrator.Testing the + and - Glug revealed that something terribly wrong with the negative Glug.Expected traces:Observed traces:

author: Kosmic
author_rank: Super Contributor
timestamp: January 25, 2019, 02:41:33 am
content: Based on the fact that the -Glug was struggling to go back to 0V, I decided to inspect and verify TR202 and then the -Glug Drive and associated transistors.To my surprise I realised that TR202 was just not there (completely missed it when quickly inspecting the board). The pads were perfectly clean and it was almost like TR202 was never soldered to the board. Might have been a case of cold joint. Unfortunately the mosfet was nowhere to be found.So TR202 is actually a WM222 (Solartron part # 300555940). Now I couldn't find any information on this part but the 7081 has the same Solartron part # for the same part in the integrator. But the manufacturer par number on the 7081 is VN67AK and specsheet is available on the web for that part. Since the Solartron part # are the same I speculated that the parts were interchangeable (WM222 / VN67AK).After a bit of search I found the Microchip VN2210 with specs equivalent to the VN67AK.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 25, 2019, 07:52:55 am
content: Surely someone had a go in it and never finished the jobIt would had never pass Solartron quality control

author: Kosmic
author_rank: Super Contributor
timestamp: January 25, 2019, 02:53:46 pm
content: Quote from: coromonadalix on January 25, 2019, 07:52:55 amIf it's the case, that person is really good at de-soldering!

author: coromonadalix
author_rank: Super Contributor
timestamp: January 25, 2019, 09:19:55 pm
content: With solder wick, you can obtain theses results ?? or a desoldering pump too ??Unless maybe unless a part was not put on the pcb, i had a problem like this in the past with an sony cinema center, a missing resistor made the speaker output drift in dc and trigger the speaker protection, but the drift was really slow in time.

author: Macbeth
author_rank: Super Contributor
timestamp: January 25, 2019, 10:09:25 pm
content: That part has been de-soldered and PCB cleaned up. You can still see some flux residue and also the solder mask show signs of heating around the pins.

author: kony
author_rank: Regular Contributor
timestamp: January 25, 2019, 10:32:05 pm
content: Quote from: coromonadalix on January 25, 2019, 09:19:55 pmYes, with decent flux and bit of practise, no problem at all.

author: Macbeth
author_rank: Super Contributor
timestamp: January 25, 2019, 11:05:13 pm
content: You can see that every one of those 8 transistors including the missing one have been played with, though the bottom ones are out of focus.Just look a bit north of the board at the diodes and resistors and note no shenanigans with solder mask, it's all clean and even.

author: Kosmic
author_rank: Super Contributor
timestamp: January 29, 2019, 04:05:13 am
content: You're probably right. Unit#2 is a lot cleaner and there is no flux residue around the transistors.This is a picture of the integrator of Unit#2

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:14:19 am
content: So replacing the WM222 by a VN2210 fixed the -Glug. Nevertheless I decided check the rest of the integrator before calling it a day.For some reason (VN2210 being not exactly the same as WM222 ?) the -Glug Drive squarewave was curving a bit.Trace 1 = +Glug DriveTrace 2 = -Glug DriveIncreasing the capacity of C808 fixed the issue. I played with different value and ended up using a 1uF tantalum capacitor.Trace 1 = +Glug DriveTrace 2 = -Glug DriveThe new transistor and cap installed on the board.

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:23:13 am
content: Unit #1 is now passing Self-Test and seem to be fixed

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:29:54 am
content: Next steps:- Teardown- Testing all electrolytic capacitors- Replacing the Schaffner filter- Replacing the memory backup battery- Replacing the input connectors

author: coromonadalix
author_rank: Super Contributor
timestamp: January 31, 2019, 04:33:45 am
content: Congrats for your repair

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:44:16 am
content: Teardown:All the 7061 PCBsPCB 13 - Digital Board

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:55:14 am
content: PCB 15 - Analog BoardPCB 8 - Oscillator Board

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:56:01 am
content: Front Panel

author: Kosmic
author_rank: Super Contributor
timestamp: January 31, 2019, 05:19:03 am
content: New NI-MH battery in placeI spent some time testing electrolytic caps but they were all fine. Now since I'm pretty much done with soldering on the PCBs, I started cleaning everything with IPA.

author: branadic
author_rank: Super Contributor
timestamp: January 31, 2019, 04:52:02 pm
content: What is the reference used in this unit?Congrats to your progress in refurbishing the meter.-branadic-

author: Kosmic
author_rank: Super Contributor
timestamp: February 01, 2019, 03:15:37 am
content: Quote from: branadic on January 31, 2019, 04:52:02 pmI think the 7081, 7071 and 7061 all use 1N829 Zener diodes.

author: Kosmic
author_rank: Super Contributor
timestamp: February 01, 2019, 04:15:21 am
content: D301A is the voltage reference

author: Kosmic
author_rank: Super Contributor
timestamp: February 01, 2019, 04:42:20 am
content: The original Fischer connectors being way too expensive, I decided to replace them by cheap XLR 12mm 5 pins connectors I found on ebay. I know they are probably not that good but I wanted the opportunity to create a lot of different test leads for the 2 meters I have.At least they are fitting on the existing front panel without any modifications.

author: Kosmic
author_rank: Super Contributor
timestamp: February 01, 2019, 04:57:14 am
content: Back connectors for rear input and secondary input channel were also replaced.

author: Kosmic
author_rank: Super Contributor
timestamp: February 20, 2019, 02:29:24 am
content: Unit #1 fully reassembled.

author: eevcandies
author_rank: Regular Contributor
timestamp: May 23, 2019, 02:06:53 am
content: I have one of these 7061 models, been sitting around at least 12 years, since I plugged in (It came up and ran fine last time). I didn't have any way of make any connections to try it out (where are the banana jacks?), so I tossed it aside & reverted to my fluke meter. I seem to remember not liking the readout, it put commas in the readings (like 12,437 V)? Or perhaps I didn't fiddle enough with it.I have a precision R6871E, which is nice, but I still use my Fluke!

author: Kosmic
author_rank: Super Contributor
timestamp: May 24, 2019, 04:00:18 am
content: I really like the 7061. The one I repaired seem to be really accurate. It's not the kind of meter you use daily on your bench but for precision stuff, it's working pretty well.The only problem is the connector. Not a problem anymore in my caseNeed to finish repairing the second unit now.

author: kblue
author_rank: Regular Contributor
timestamp: July 01, 2024, 04:05:45 pm
content: Old topic, i know ... just don't want to create something new.I too now own a 7061 and i like it. What was your exact replacement for the Schaffner Filter? Just a new Schaffner? Are these XLR sockets the "mini XLR" variant?My meter seems a tad out compared to my trusty 2024 calibrated (company did the cal) FlukeA 10,00000 source reports as 10,000244 +/- with the 7061 and 10,00001 +/- with my Fluke. The manuals show how to "calibrate" the meter (digital i guess) but it seems, i need to do that for every range. The readings so far seem to be stable, just not as "accurate" as it could. Mayhaps its something else, i wasnt able to check the insides yet.Oh, and the Ni-MH battery is replaceable anytime? Or does the meter need to be powered on? Some devices do lose the cal if powered of and battery removed.Best wishes!

author: Kosmic
author_rank: Super Contributor
timestamp: August 12, 2024, 09:29:39 pm
content: Quote from: kblue on July 01, 2024, 04:05:45 pmThe Schaffner FN372-2/21 is still avaialble.https://www.mouser.com/ProductDetail/Schaffner/FN372-2-21?qs=62ecY7oL%252BWNQsCxHqtpJ8A%3D%3DQuote from: kblue on July 01, 2024, 04:05:45 pmI ended up going back to the original fischer connector since I found some original test leads. I don't recommand using any cheap XLR connector as I did.An alternative to the fischer connector would be good quality standard 4mm banana binding postshttps://www.eevblog.com/forum/repair/repair-of-solartron-7081-sn718/msg4031680/#msg4031680.Quote from: kblue on July 01, 2024, 04:05:45 pmYou can replace the battery when powered off since calibration is stored on non volatile ram.

author: unseenninja
author_rank: Regular Contributor
timestamp: August 13, 2024, 07:54:06 am
content: Quote from: kblue on July 01, 2024, 04:05:45 pmCheck the insides as soon as you can. You will most likely find the battery leaking. The original battery would have been a NiCD battery. Replacing it with a NiMH is a really bad idea as they don't like being trickle charged and will leak even more badly than a NiCD. Here's the mess that I had to clean up on one of my 7061 meters:The board needed to be cleaned with vinegar to start with to neutralise the alkali which had leaked from the battery. Then all the solder resist needs to be scraped off as the alkali finds its way under the solder resist and spreads even further. I replaced the battery with a supercapacitor. It easily lasts three months before it runs out of power. All the replacement parts need soldering on both the top and bottom of the board as the plated through holes get destroyed by the leaking electrolyte as well.

author: factory
author_rank: Super Contributor
timestamp: August 13, 2024, 10:43:19 am
content: Quote from: Kosmic on August 12, 2024, 09:29:39 pmThe original Fischer connectors should still be available, but with a minimum order to obtain;https://www.eevblog.com/forum/buysellwanted/group-buy-fischer-connector-plug-s104-a053-130/There are lower cost clones of the Fischer connectors;https://www.eevblog.com/forum/metrology/solartron-7081-reference-circuit/msg5580701/#msg5580701https://groups.io/g/Solartron_Schlumberger_Equipment/topic/input_connector_cable/103448605David

author: kblue
author_rank: Regular Contributor
timestamp: August 26, 2024, 11:32:17 pm
content: Thanks for the reply. I ordered some new parts (including a supercap, same as in the picture unseenninja.The only thing "missing" would be the calibration-key or another solution. The meter seems a bit out. 10.00000 VDC input with my fluke 8506a (recently back from calibration) shows 10.0004X (x is fluctuating a bit). Mayhaps it's because of bad testleads, as i am still waiting for the proper input-jack and stuff i ordered.Calibration seems straight forward with this meter. As far as i understand the manual, all "VDC" ranges need to be calibrated separately? The example in the manual is about the "10 VDC" range.Apart from that, i do love the blue digits. Even though, replacement of this VFD could be a problem in the future.Best wishes!

author: kblue
author_rank: Regular Contributor
timestamp: December 03, 2024, 09:26:55 am
content: Still looking for a key-replacements or another solution like ... known pin-layout what connections needs to be shorted/open for Cal/NonCal-Mode.Thanks in advance!

author: factory
author_rank: Super Contributor
timestamp: December 03, 2024, 05:25:40 pm
content: There must be someone nearer to you, that could take a cal key to a cutting shop & get a copy made, I thought they all used the same type?Edit: someone is already selling copies on ePay;https://www.ebay.de/itm/255643980121David

author: unseenninja
author_rank: Regular Contributor
timestamp: December 04, 2024, 08:17:22 pm
content: I can vouch for the keys from that seller. They work in all Solartron meters of that time, including the 7061.

author: Kurets
author_rank: Regular Contributor
timestamp: December 05, 2024, 06:01:11 am
content: I have hand filed a key and can provide a drawing for you if you like. I also have two key blanks that I could provide if you are in Europe. Maybe I could file the key for you, but I am getting ready to move house so I don't know that I'll have the time anytime soon.Edit: I see that you are in Berlin. I think that I bought my key blanks from Germany, so I will look this up and get back to the thread with more info.

author: Kurets
author_rank: Regular Contributor
timestamp: December 05, 2024, 07:54:56 pm
content: The key blank I used was a Silca RO21, this is available from Ebay and is a profile/length match to the one used originally by Solartron. The attached picture shows measurements on a picture of a genuine key. I used only the measurements from the picture along with the paint+try method for checking interference in the actual lock. In the end I got a working key within about 1-2hrs of elbow grease.I could not find my spare blanks today, but this link has some in stock in Germany:https://www.ebay.co.uk/itm/254721466397

author: factory
author_rank: Super Contributor
timestamp: December 05, 2024, 08:24:47 pm
content: There seem to be some switch keys available online as "Ronis 601 switch key", that look very similar to the key I have, no idea how close they actually are.David

author: unseenninja
author_rank: Regular Contributor
timestamp: December 05, 2024, 10:28:16 pm
content: Quote from: factory on December 05, 2024, 08:24:47 pmI think all these keys are identical. Given the very clear pictures here, Kurets' measurements and identification of the exact blank needed, I'd say the bottom just fell out of the eBay seller's market. A set of needle files, a blank and a caliper is all that's needed to create one of these keys.I've picked these locks before and they take about ten seconds with a simple rake, so it's not as if the key requires micron tolerances.

author: Kurets
author_rank: Regular Contributor
timestamp: December 06, 2024, 09:47:43 am
content: Indeed, the key is low tolerance and the profile of the blank is very common. This site lists more alternative part numbers for the key blank:https://www.aldridgesecurity.co.uk/silca-1697-silca-ro21-to-suit-ronis.htmland depending on your country one or another may be more available.When I was making my key I actually had the turning direction of the lock wrong for a while, so I very much over-filed mine but it still works well. So as long as you have patience, and maybe one spare blank in case you make a mistake, there should be no reason to not have a cal-key. I added a picture of my DIY key, which is clearly not quite the same as the genuine key.

author: kblue
author_rank: Regular Contributor
timestamp: December 06, 2024, 02:09:54 pm
content: Thanks for all the input! Ordered some keys (-:The final step would be to find someone here in GER to do aalignment+ cal. I know my unit is a bit out of spec with a single known source (measured with a 3458A). Sadly every ... single ... range ... needs to be aligned separately.

author: Kurets
author_rank: Regular Contributor
timestamp: December 09, 2024, 11:47:04 am
content: To hijack the thread a little. My unit has a NiMH battery fitted, replaced 2017 according to a sticker on the unit. I see that there is quite some corrosion which I have tried to clean up with vinegar, but did not clean-off the soldermask etc.I am thinking of installing a supercap like described above, but I was also thinking that an alternative option would be to install a lithium cell and and replace R501 with an LTC4054 set to low charging current (50mA or so). I guess changing one battery for another would have the same problem in the end? But wouldn't a supercap also be a leakage risk? I don't know the relative nastiness of the different solvents used.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 09, 2024, 12:44:24 pm
content: supercap would not be a problem if you respect it's operating voltages ...ok we did saw some leaked ones in the past, never saw on modern ones ...the higher capacity it as, the longer it needs to be charged ...

author: unseenninja
author_rank: Regular Contributor
timestamp: December 11, 2024, 02:57:08 pm
content: Quote from: Kurets on December 09, 2024, 11:47:04 amThat may come back and bite you. As I said, the battery electrolyte seeps under the resist and keeps on spreading. I first used some dilute spirit vinegar, then lots of water and finally isopropyl alcohol.As the supercap I used is rated at 5.5V, way above the nominal battery voltage, there's very little chance it will leak.

author: ve2ulu
author_rank: Contributor
timestamp: February 28, 2025, 07:19:28 pm
content: I change all 7805 regulator on cpu board for switching regulator 3 wire module.I reduce heat and cute the power input of the meter mostly half!I disconnect 7805 with solder jumper, keep all original part on pcb and wire the new regulator over, no need heatsink or thermal contact.The big capacitor, transformer and bridge have less work.