General Resistance DAS56A - Page 1
Forum section: electronics / general

author: MosherIV
author_rank: Super Contributor
timestamp: October 21, 2016, 11:30:58 pm
content: HiI recently got a General Resistance DAS56A dial a source.1V range resolution 1uV10V range resolution 10uV0.005% accuracyTC - 2ppm/C24H stability 10ppmnoise 10ppm or 30uVp-pFull specification and schematic in the manual :www.eevblog.com/forum/testgear/i-don't-need-no-stinking-calibration/?action=dlattach;attach=51658I got it to test the calibration of my DMMs, including Thurlby 1905a (5.5digit) and Solartron 7060 (6.5digit)Fortuneately the company I work for has allowd me to verify my voltage sources/standatd with a recently calibrated Tektronics DMM4040There are 3 things I would like clarification/guidance on please?1. Noise.The manual has some brief instructions on calibration, where the first thing that needs to be done is to set the zero offset.Now the instructions say to try and set the offset to somewhere below 5uVThe problem is that the base level noise is 30uV - how do I set the zero offset when the base level noise swamps the readings?2. DriftSo I did my best to set the zero offset but I noticed that after setting it, after lunch the zero offset has drifted.Is this normalor is there something wrong with the unit?I have attached a spreadsheet showing the noise measured by the DMM4040I have also attached another spreadsheet showing the long term drift over 5 hours with the outpiut set to max - 10V3. last 2 digits of KVDIt looks like the last 2 digits of the Kelvin Varley Divider are not working properly.I noticed that in 10V mode, sometimes 100uV range does not work properly.(the base level noise makes the last digit meaning less - is that what you would expect ?)When I set any voltage below 1V (in 10V mode) the 100uV range worksWhen I set the MSD to 9V - the 100uV digit does not match the settingDoes this mean there is something wrong?Is it the voltage reference?Or is it the KVD selectors need cleaning?

author: MosherIV
author_rank: Super Contributor
timestamp: October 21, 2016, 11:35:25 pm
content: BlastHow do I attach files like spreadsheets please?(I tried zipping it and uploading but they do not show )

author: Vgkid
author_rank: Super Contributor
timestamp: October 22, 2016, 12:35:48 am
content: A zip file should work. Attachments should accept xls/ods files.

author: zlymex
author_rank: Frequent Contributor
timestamp: October 22, 2016, 02:30:18 am
content: Quote from: MosherIV on October 21, 2016, 11:35:25 pmMay be try to save the spreadsheets in .xls extension instead of others suhc as .xlsx

author: MosherIV
author_rank: Super Contributor
timestamp: October 22, 2016, 09:04:16 am
content: OK lets try .xlsAny thoughs on my 3 issues please?1 noise2 drift3 problem with KVD contacts?

author: Andreas
author_rank: Super Contributor
timestamp: October 22, 2016, 12:55:11 pm
content: Hello,1. The noise is given as wideband noise. You are integrating with 10 NPLC. So the noise is largely reduced.As long as the noise is gaussian you can average the samples until the noise is small enough.I would also consider to use 100 NPLC.2. is the drift related to the source or to the DMM? the last 10000 measurement values look quite constant.Most instruments need at least 2 hrs warm up time.With best regardsAndreas

author: MosherIV
author_rank: Super Contributor
timestamp: October 27, 2016, 08:33:05 am
content: QuoteMissed the question the first time I read the reply.I am pretty sure it is the source, but how would I find out for definite?Yes, it has been overcast these past days and the output was pretty stable after warm up (I give it about 1.5 hours).I sitting with my back to a window at work and it seems the sun was affecting the readings, cauing what looks like drift. I noticed this in the graph above, I realised it was sunny in the morning and went overcast in the afternoon when the reading stablised.I think there is something wrong with it. It can set 100uV when the total output is < 4V but as soon as it goes above 4V it reads low by 20/30uV ie3.00010V is ok get 3.00014 or 3.00015V4.0001V gives 4.00007VI think the contacts on the KVD must be dirty. Any suggestions on what to use to clean?I read about similar Datel calibrator and it said to use IPA and lubricant, what lubricant should I use, eg WD40?

author: MosherIV
author_rank: Super Contributor
timestamp: October 27, 2016, 10:25:37 am
content: It turns out I did not need to worry, access to the contacts for the first KVD decade was very good :I have done a full tear down here :https://www.eevblog.com/forum/testgear/general-resistance-das56a-tear-down-and-repair/msg1057652/#msg1057652It will have to wait till Mon now until I get back into work to see if cleaning the contacts has made a difference.

author: GeneM
author_rank: Newbie
timestamp: October 31, 2016, 02:40:40 am
content: I have both a DAS 46A and a TSC 46 and both had minor issues when I bought them-several months apart and from different EBAY sellers. Before messing with the contacts in the Kelvin-Varley divider, you should take a look at the power supply board and the Chopper-Stabilized Amplifier board. Towards the left side of the power supply board is a daughter board which is actually the Chopper-Stabilized Amplifier. It's very easy to miss the fact that it is socketed onto the power supply board. You can see the CSA daughter board in your tear-down picturehttps://www.eevblog.com/forum/testgear/general-resistance-das56a-tear-down-and-repair/?action=dlattach;attach=265549towards the left side of the power supply board.My DAS 46A had very unstable output readings until I lifted the corners of the CSA board and re-seated it onto the power supply board. It was not necessary to fully lift it. After re-seating it, the output was very stable and very easy to zero with the 10-turn pot at the top edge of the power supply board. Short circuit the meter's leads and make sure it shows '0.' Then set the Kelvin Varley to zero, connect the meter and it should also show zero-well, adjustable to within 5 micro-volts of zero.As an aside, I'm using an HP 3455A bought through EBAY and repaired through several weeks of finding a few minutes at a time to learn how some portions of the circuitry worked. I've bought four of them (different auctions) in non-working condition and currently have two of them working.The second thing I did to get my DAS 46A reliable to use was to take advantage of what I learned with the TSC 46. Although it has additional circuitry for thermocouple calibration, in one mode it fully duplicates the DAS 46A as a voltage reference. There is very little inside the transformer enclosure-just some bridge rectifiers and 1 Micro-Farad capacitors-so I wouldn't go in there just yet.Instead, look at the power supply board. It uses a clever circuit which only needs only one 1N752A zener diode as a reference for both the + and - 15 volt power supplies that feed the CSA board. I believe that tries to ensure that both + and - 15 volt outputs drift together, improving stability of the CSA.Another voltage regulator circuit provides 1N752 zener stabilized power to the two series-connected 1N827 zeners in the other 'box' located below the Kelvin Varley divider. That also looks like some gray-beards implemented a very carefully orchestrated circuit with a lot of selected & matched 0.01 % resistors used to partially offset the 1N827 temperature drifts. The care they took is incredible. On my TSC 46, I first replaced only the one 50 Micro-Farad capacitor (with a 220 Micro-Farad) which had failed some time before I had bought it. Replacing the one capacitor brought it back to life. I used it for many weeks while working on one of the broken 3455A meters, but then one day the TSC 46 became unstable again. The other 50 Micro-Farad power supply capacitor (-15 volt side) had failed. So, I replaced all of the 50 Micro-Farad capacitors with 220 Micro-Farad capacitors just to avoid having to do it piece-meal. They were vintage 1979, so that was not a bad service life.I don't have anything good enough to calibrate my 3455A meters. But I did buy one of those LM584 references on EBAY which had been measured by the seller's 'still in calibration period' Agilent 34401 to give me a ball-park check. I set the DAS 46 to match the seller's 34401 measurement at each of the four settings and made the following table.Note the LM584 reference outputs were supposedly 2.49980, 4.99829, 7.50249 and 10.00001. The third column shows the readings of the LM584 reference from my repaired 3455A.DAS 46 Setting 3455A "LM584" Reference per 3455A:2.49980 2.49976 2.499774.99829 4.99824 4.998327.50249 7.50241 7.5025210.00000 9.99989 10.00010While I don't know truly how close the DAS 46 is to 'spot-on,' I do have some confidence that it is not terribly far off. To those who designed and built the General Resistance devices-you should be very, very proud of yourselves.So, I'd start by reseating the CSA daughter board and replacing the 50 Micro-Farad power supply board capacitors before I'd take apart the gold-plated Kelvin Varley six-decade divider. Put an oscilloscope on the voltage regulator outputs and make sure they are not noisy. The CSA can't give clean output without clean power.

author: MosherIV
author_rank: Super Contributor
timestamp: October 31, 2016, 02:07:43 pm
content: Hi GeneMI had noticed the PSU board has the Chopper-stabilized amplifier board as a daughter board.I had not considered this to be the source of the problem. I will definitely, re-seat it to see if this helps.I have already tried cleaning the first KVD contacts, it made a small difference as far as I can tell.I will try your suggestions out.As far as the 'LM584' - did you mean AD584?The AD584 has far worse noise than the DASThe data sheet says "NOISE (0.1 Hz TO 10 Hz)" = 50?Vp-pWhere as the DAS56A/47A is 30?Vp-p

author: GeneM
author_rank: Newbie
timestamp: November 02, 2016, 02:10:57 am
content: Yes, I'm sorry- it was a AD584KH reference. Your equipment is far better than what I have. I had not thought to put an oscilloscope on the output of the DAS 46, though I have looked at it with several multimeters. The only oscilloscope I have is a 'low mileage' B&K Precision 1476A which I bought new in the mid 1980's. It's never been calibrated and it only has a 10 MHz bandwidth. Also, the most sensitive scale it has is 1 millivolt per division. I had thought it would be useless for this sort of thing and so that may have contributed to my not having looked at the output with it. It was very useful in showing the DC power supply's capacitors had failed.The B&K 'scope shows what appears to be about 2 millivolts peak to peak of noise on the DAS 46's output. But it shows the same on each of the two AD584KH references. Neither of my 3455A meters gives any indication that the output is noisy. They bobble by one or two counts at most at any setting I've tried even with 'high resolution' set to give me the full 6.5 digits. So I'm concluding that my old B&K just isn't up to the task and it's readings are really only telling me that I need a much better scope for this sort of work.I've read that Zener diodes are noisy, but the output from the Zeners in the DAS does get filtered through a three-stage RC filter before it gets to the Chopper Amplifier. Any Zener noise should be very quiet as it enters the CSA. That's why I was first suspecting the power supply capacitors and the socketed connection to the Chopper Amp rather than the Kelvin-Varley. It is always possible that your DAS was not well-treated and it could have seen a contaminated environment.There is also noise from the 1N752 Zeners in the power supply and there is voltage gain to go from the zener's 5.6 volts to the power supply's 15 volts. The 50 Micro-Farad capacitors (220 Micro-Farads in each of my DAS / TSC 46) at the input and output of the 15 volt regulators should prevent that from being a noise source.Since you've got the (far, far) better scope, you could try looking at the five 'stages' of this device for noise and then we'd have a much clearer picture of where the noise is coming from. It is also possible that your scope's microvolt scale is not really 1000 times better than my B&K 1 millivolt scale and we're really looking at artifacts of that scope's limits. I'm not saying, implying or even suspecting that is what is happening because I have no experience with really good equipment such as what you have and so I don't know how it behaves when it is being used at microvolt scales. You can teach me.Stage 1 would be at the power-line input. The DAS has an RFI filter which should act to block any noise coming in through the AC power line. But these machines are 30 plus years old and we have no way to know if they have been over-stressed at some time, so we can't take it for granted that the power filter works-or even that it's not oscillating. Your scope can tell us.Stage 2 would be the outputs of each of the +15, -15 for the CSA and +24 for the Zener regulator assembly to ensure there is not significant noise from those sources. Zeners are noisy and there is voltage gain in those circuits, so a bad zener there could throw noise into the CSA or the Zener regulator assembly.Stage 3 would be to look at the output of the Zener regulator assembly to see if you have a breaking-down or wildly noisy 1N827A in the voltage regulator assembly. If the noise is from a noisy 1N827A, then it should be a higher voltage here than anywhere else because that assembly puts out about 12.4 volts which is cut-down before getting into the Kelvin-Varley by 12.4 / 10 (it's much more precise than I'm making sound)Stage 4 would be to look at the input to the Chopper Stabilized Amplifier from the 1N827A diode pair in the regulator assembly after it has come through the three stage RC filter. Zener noise should be lower here than at the Zener Regulator assembly output both because it has been reduced to at most 10 volts and because of the RC filter that is supposed to filter the input to the CSA from the Zener assembly. One or more of those three 1 Micro-Farad capacitors could have broken down or one or more of the resistors opened or nearly opened (or bypassed by some chemical deposits on the board) and so it would not be performing as it should. There is less shielding from external environment here than in the Zener Regulator assembly or the Kelvin-Varley. If the Kelvin-Varley was infiltrated by some chemical agent in the environment, then the RC filter would have seen an even greater concentration of whatever agent it was.Stage 5 is where you've already measured-the output of the CSA. If the noise is being generated by the Chopper Stabilized Amplifier, then it should be greater at the output than at the input. The CSA actually is supposed to have a voltage gain of 1.000000, so the output should be exactly like the input except for noise contributed by the CSA. I have not found a schematic diagram of the CSA, it seems to have been a trade secret of the General Resistance Company. If yours is bad, then you may want to try replacing it with a modern single-chip CSA.Alternatively, if you only use it with very high input meters, then you may just take the CSA out of the circuit and run the Kelvin-Varley's output directly to the output jacks.I don't get to work with my hobbies much, so I may not respond very fast. I'll try to make a greater effort because I'd really like to know more about these devices and you've got the equipment needed to do that.

author: MosherIV
author_rank: Super Contributor
timestamp: November 02, 2016, 05:07:25 pm
content: QuoteActually, neither have I (yet). I do mean to put a scope on it at some point.The figures I quoted for noise are from the specifications.A 6.5 digit meter should be able to see noise in the 100s uV, 10s uV and possibly 1s uVThe Solartron 7060 (6.5 digit) meter is fast enough to see the noise fluctuations in 10s uV, this is the one I have at home.The Tektroncis DMM4040 (6.5 digit) meter is fast enough to see the noise fluctuations in 10s uV, this one I am using at work (where I have taken the picture at the top of this thread).The Thurlby Thandar 1905a (5.5 digit) meter performs similarly to your HP 3455A - the update rate only sees a small change in lsd count. i have this one at home.I think the problem is the update rate of the meter. The 6.5 digit meters I have and am using are capable of measuring 100s of times a second - hence can see the noise.Quote10MHz bandwidth should be fine, we are just measuring low freq noise. The issue, which you have identified, is the resolution of the lowest range, 1mV is not enough resolution.I have tried re-seating the CSA board and I think it has helped with the drift.I have not tried checking the PSU rails and changing the 50uF caps yet. Maybe I will get a chance over the weekend.Yes, I agree with the 5 steps you have suggested, just need time to do them

author: Andreas
author_rank: Super Contributor
timestamp: November 02, 2016, 07:43:00 pm
content: Hello,I think the scope is ok.What you need is a shielded box and shielded wires for the measured device.Otherwise you get influence by mains line frequency.Try a cookies box and battery supply for the AD584.See also AN124http://cds.linear.com/docs/en/application-note/an124f.pdfwith best regardsAndreas

author: villas
author_rank: Newbie
timestamp: November 03, 2016, 01:08:47 am
content: Hi MosherIV,I got some months ago one DAS-57AL and I have a HP3456a, but no means (GPIB adaptor) to create a long log of measures.But I can tell my experience with the last digits. My unit agree to HP3456a (uncalibrated) except for the 2 last digits, in both ranges 1V and 10V. In 1V range the last digit (100nV) doesn't seem to work properly, the 6th digit (1uV) works ok but have some offset, this offset looks stable in short term, but varies from one day to another by several micro Volts.I disassembled my unit, it doesn't have the KVD shielding, and someone had already changed the electrolytics. Now, with all the good information on this post, I will probably open it up again and check on CSA board, also probably try to make a shielding for the KVD.As soon as I get one GPIB I'll try to make some noise and drift graphs.

author: MosherIV
author_rank: Super Contributor
timestamp: November 07, 2016, 05:53:53 pm
content: So I took it apart again over the weekend and gave the end (first KVD) contacts another clean.Also tried to clean the PCB surfaces of the other KVD dividers as best I could without taking the whole KVD assembly apart.Seems to have made a difference - I can now set 9.0001V and measure 9.0001V.While I had it apart I did a few measurements.I first checked the supply rails for noise (across C4)It is kind of hard to see but you can just see a bit of ripple on the supply rail.Bear in mind that is a x1 probe and the scope is on the max gain (2mV/div)

author: MosherIV
author_rank: Super Contributor
timestamp: November 07, 2016, 05:59:03 pm
content: At this point I was kind of OK with uV of noise.Later I came back and checked the output. I had the time base in the usec and the noise looked OK but when I changed the time based to a slower setting, I saw more noise I had not noticed before.Sadly, I had put the thing back together at this point and it was late so I did not have time to take it apart again and check the supply rails or even check the rectifier outputs.Another job for this weekend.

author: Vgkid
author_rank: Super Contributor
timestamp: November 07, 2016, 08:34:42 pm
content: Nice job with those contacts. Always suspect power supply issues.

author: MosherIV
author_rank: Super Contributor
timestamp: November 12, 2016, 04:47:56 pm
content: So I had a chance to have a look at the noise issue.I started by looking at the PSU, and I was shocked by how much ripple there was around 4V of ripple.I did as GeneM suggested and replaced the 50uF smoothing caps for 220uFThe ripple is down to less than 1V and the noise seems to have gone, still get some noise.Will have to wait till Monday when I get it back in the office at work and check with the calibrate 6.4 digit Tektronix DMM4040Before caps changedAfter caps changed

author: MosherIV
author_rank: Super Contributor
timestamp: November 14, 2016, 06:08:39 pm
content: I have had a chance to check the DAS56A with the Tektronix DMM4040 - no changeWhile it looks like the first stage capacitor replacment got rid of this noise :Looks like this noise is still there :The DMM shows there is 20uV of noise

author: MosherIV
author_rank: Super Contributor
timestamp: November 21, 2016, 03:53:44 pm
content: So I did some more debugging this weekend and here is what I found :While probing around for the source of the 20uV noise I figured something out - the source of the noise is not from the Chopper Stabilized Amp, it is completely asynchronous to itIn this picture, I found a nice looking square wave on the CSA board and I am looking at the noise on the +15V line.You can see there is no correlation between the square wave and the noiseI also found the noise is still there when the power is off ......Hmmmmm

author: MosherIV
author_rank: Super Contributor
timestamp: November 21, 2016, 03:57:25 pm
content: During the week, I used a digital scope to look more closely at the noise :In the second picture, the noise spikes occur at 53KHz freq.I realized on the weekend talking about it to friends/colleagues that the noise is PC PSU switching noise.Remeber, I found the noise is still there when the unit is turned off ! - Ahah moment.Additionally, I was able to see/measure the noise more clearly - 40uV p-pIt could be that I get less noise when using the analogue scope because it is a different location with different set of PCs on the mainsIn any case, I think the source of my inaccuracies from the precision voltage source is being swamped by noise from the mains.

author: MosherIV
author_rank: Super Contributor
timestamp: November 21, 2016, 04:12:41 pm
content: The DAS56A already has a mains input filter built into the design. I have circled it in red.The question is, it is eithera. not working properly - 1000pF caps gone bad? Do inductors go bad?b. not good enough for modern applications (it is 40 years old and there were no PCs with SMPS back then)?Looking at the diagram on the top of the IEC filter, it looks like the design is missing the cap between live and neutral.Can I just add the capacitor in? What value (another 1000pF)?Why are those ones(https://www.eevblog.com/forum/testgear/general-resistance-das56a-tear-down-and-repair/msg1075293/#msg1075293)so big ?Are modern oneshttp://cpc.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15002&langId=69&storeId=10180&categoryId=700000033502&eq=N%3D220842%2B411%26amp%3BNs%3DP_STORE_MARKETING_RANK_FARNELL_CPC%257c0%257c%257cP_MAN_PART_NUM%257c0%26amp%3BNtpc%3D1%26amp%3BNtpr%3D1&pageSize=100&showResults=true&aa=true&pf=110193699&vw=OK ?ORShould I fit one of these :http://cpc.farnell.com/schurter/5500-2077/1-phase-line-filter-medical-m5/dp/FT01659Any thoughts or advice welcome

author: Gyro
author_rank: Super Contributor
timestamp: November 21, 2016, 08:32:27 pm
content: Across the line capacitors tend to be PP film type in the 100nF range (Class X1 rated). Whether it will help or not depends on whether the noise is common mode or differential. It's pretty unlikely that those 1000pF capacitors have gone bad (or the inductors either). Depending what the caps look like, it might be worth replacing them with modern Y1 rated ceramics anyway (the ones fitted may not have current safety ratings).It's a bit of a sad lesson of older equipment struggling to survive in our modern SMPS polluted world!

author: MosherIV
author_rank: Super Contributor
timestamp: November 29, 2016, 05:47:18 pm
content: I had an old IEC encapsulated filter connector lying around.As a test, I disconnected the filter in the DAS56A and put the ICE filter in.I powered it up and checked the +15V rail ...... the noise is still thereMy only other hope now is something like this :http://cpc.farnell.com/wurth-elektronik/74271221s/ferrite-core-split-10-5mm/dp/FT0165769?ost=FT0165769&selectedCategoryId=&categoryNameResp=All%2BCategories&searchView=table&iscrfnonsku=falsebasically a ferrite that clamps around mains cable.Something else I am going to try is to put together a shielded cable.The noise is 10 uV (microVolt) p-p on the scope. I would really like to get it down to less than 10uV p-p then I have more confidence in the 5th digit of the unit.Right now the unit is only good to the 4th digit, ie 1mVAny thoughts or advice welcome

author: MosherIV
author_rank: Super Contributor
timestamp: December 07, 2016, 08:24:18 pm
content: So I made a bit of progress, I got a couple of ferrite clamps and they seem to make a difference.Here is a picture of the noise beforeHere is a picture of the noise with the clamp on the mains inputAnybody know what the parameter associated with them would make the biggest difference?

author: r6502
author_rank: Regular Contributor
timestamp: March 24, 2021, 08:31:55 pm
content: Hello all,I also own one DAS 56A. Mine has now 2 problems:1st the reference broke down, so I build a new one, based on LM3992nd after I moved, the CSA was not working any more - it output is always on the positive rail (about 13,8V)I checked the power supply - it is fine at +/- 15V DC, I checked the reference voltage - all fine at 10V (+/- some 10µV) I checked the input filter for the CSA, Caps are fine, isolation resistance is ok, and capacity is also fine as well as the 3 resistors.I also removed the CSA from it's socket and placed it back - same result.So my thought is, the the CSA has a defect. Does somebody have a schematic of this PCB - in the manual you find a black box for the CSA ...I do not find a schematic for this, so I'm thinking to do some reverse engineering, if nobody has a schematic for this, but this will take some time. On this board there are 2 good old boys: LM308, sitting in the metal can - I love it to work again ...Kind regardsGuido

author: chuckb
author_rank: Frequent Contributor
timestamp: March 24, 2021, 09:26:21 pm
content: To block the high frequency noise on interconnect lines I use the Fair-Rite 0475164281 clamp-on ferrite bead. It uses type 75 Material with peak impedance around 1 MHz (100 ohms). This model has a 0.25" ID. The 0475164181 Model has a 0.5" ID. For broad band performance use two different type of beads on the interconnect lines.I use these on the power line and input cables of Nano-voltmeters to reduce EMI from a local 1 MHz broadcast station. I must have 30 of these around the lab for the sensitive instruments.

author: r6502
author_rank: Regular Contributor
timestamp: April 02, 2021, 11:32:14 pm
content: Hello All,I just figured out the layout of the CSA inside the DAS 56A.red lines: tracks top layergreen lines: tracks bottom layeryellow dots: padsinteresting thing: in the schematics of the DAS they do not show the GND pin for the CSA...The schematics will follow ...Guidoedit: updated graphic with white background, spelling

author: r6502
author_rank: Regular Contributor
timestamp: April 11, 2021, 12:04:04 pm
content: Hello All,I just finished the schematic for the CSA inside the DAS devices.This represents the schematic of my board. Any comments are welcome.There are questions regarding the parts:T6: This MOSFET is marked as "MFE300" on its housing, but I did not find any data on this MOSFET type. It is also a N channel type MOSFET.D6, D7: Marking on is not readable.Guidoedit: infoe on T6, D6 and D7

author: kleiner Rainer
author_rank: Regular Contributor
timestamp: April 11, 2021, 05:53:19 pm
content: Guido,I checked my old ECA Data Books from the eighties, but there was a distinct "hole" between MFxxx and MFE3002, so no MFE300 to be found.The Motorola Databook on bitsavers.org also only gave data for the MFE3002. Did you check the lettering with a magnifier? Sometimes the lettering rubbed off or was not fully printed to begin with.Here the link to the Motorola data book:http://bitsavers.org/components/motorola/_dataBooks/1974_Motorola_Discrete_Semiconductor_Series_A_Vol3_Non-Registered_Type_Numbers.pdfDatabook page 310, PDF page 327 has the datasheet for the MFE3002. Maybe the MFE300 is a selected version?Greetings,Rainer

author: r6502
author_rank: Regular Contributor
timestamp: April 11, 2021, 07:13:58 pm
content: Hello Rainer,that's great - Thanks.meanwhile I found another post, also on EEV blog, where the user wrote, that there are two MOSFETts of the type MFE3002 assembled:https://www.eevblog.com/forum/repair/sub-for-mfe-3002-mfe3002/Guido

author: r6502
author_rank: Regular Contributor
timestamp: April 16, 2021, 08:46:14 pm
content: Hello all:Update schematic CSA:I mixed up gate signals of T5 and T6. It is corrected in rev. 01 of the schematic.Kind regardsGuido

author: bastl_r
author_rank: Regular Contributor
timestamp: February 13, 2022, 05:39:51 am
content: HelloI has a GR Voltage Standard too. Its Name ETS15.There is also the same CSA build in. But the output voltage is maximum 1V.My CSA is not stable. The voltage is drifting a litlle up and down.Once i built another CSA with an TLC2652 but its not powerfull enough.Now with the schematic i can look for the bug again. Thank you for sharing.bastl_r

author: r6502
author_rank: Regular Contributor
timestamp: March 14, 2022, 12:28:22 pm
content: @bastl_r:thanks for the reply.Did you include a outplut transistor stage in your design, or did you just use the output of the TLC2652 ? The TLC2652 has only +/- 5V (abs. Max: +/-8V) supply, so, it is fine for a max output of 1V, but not for the units with 10V output.I'm not getting the defect mosfet's for the chopper amplifier, and the russian replacememts did not work, so I think, that I will use a LT2057 followed by an output stage simmilat to the original design.Guido

author: bastl_r
author_rank: Regular Contributor
timestamp: March 17, 2022, 03:17:09 am
content: HelloThe ETS15 has only +/-6V on the CSA and max +/-100mV at the output.But it ist not working perfect with the big cap on the output.Now i will try to change the Transistorchopper with the TLC2652 or a new LT2057 and use the Transistorstage to power the output up.There are only small differences of resistorvalues between my CSA and the CSA from your DAS.I'm at work now and will post more details later.regards

author: bastl_r
author_rank: Regular Contributor
timestamp: March 19, 2022, 04:10:43 am
content: When the device is at rest it starts to drift away. Over 8 hours it is about 5 - 6 µV.If the polarity selector is set from + to -, the continuously measured reference voltage before the KVD is reduced from 99.915mV to 99.897mV. This can be repeated at any time with different output voltages. I have no explanation for myself where the extra load on the reference voltage should come from. I have attached a circuit diagram.It is on the last page of the attached pdf.The CSA is exactly the same as in the DAS56 CSA with small value changes to resistors.For R10 a bridge is inserted.R24 and R25 have only 33Mohm instead of 100M.R27 is a 9K1 instead of 3K9T3 is a 2N4250I will now try to place a LTC1052 on the CSA board and connect it as sketched in the schematic. Or is there something against it?Regards bastl_r

author: r6502
author_rank: Regular Contributor
timestamp: March 30, 2022, 11:15:00 am
content: HJello bastl_r,I'm planning something similar, but I'd like to try the LTC2057 for this. But did not try it yet ...Guido

author: r6502
author_rank: Regular Contributor
timestamp: March 16, 2023, 09:30:25 pm
content: Hello All,It took a while, but today I was able to update my DSA 56A and perform a first test.In my unit, one of the reference diodes are defect on the original 5001-0048b reference board. I decided to install a new reference board, based on the LM399. The new reference board fits in the same small box like the old one, and uses the same connections. To be able to use the original reverence supply I did adjust the output voltage to 18V, but this was not enough, as the old reference board was consuming less power then the new one especial at startup when the LM399 heater powers up. To be able, to get enough power at startup I modified the power regulator for the reference by decreasing the resistor responsible for current limitation. Original 16R was installed, now replaced by 3.3R.On my Unit the CSA is also defect, and so I generated also a replacement for this board, based on the LTC2057 and the original output configuration with 2N2219 and 2N2905. Both schematic's are attached to this posing. Here I think is not mutch to say, have a look at the schematic - it is relay simple. as connection pins I used sub-d type male turned contacts, that have the same diameter than the contacts from the original CSA.I did also an update on the power input port. I removed the direct connected line cord and made a cut-out for for an IEC input with integrated fuse holder. The internal line wiring, the transformer connection and the line switch have been insulated now. The line filter I left untouched for the moment.First test after assembly looks promising. Next step will be a real performance check.Please have also a view on the attached PDF documentation and photos.GuidoEdit: spelling