Vintage Teardown and hopefully repair: RFT G-1001.500 Benchmultimeter - Page 1
Forum section: electronics / testgear

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 10, 2014, 08:49:46 pm
content: Hello Forum,I am on to a teardown again. This time it is going to be a digital Benchmultimeter. Again I will do this in Parts, and here we go:Pt. 1: The OutsideClick here forPt. 2.1: Topless miss PiggyPt. 2.2: Topless part pornPt. 3: Flipping out the PCBPt. 4: Schematics of the top PCBPt. 5.1: Lifting the skirtPt. 5.2: I want her naked!We are talking about the "RFT DC AC R I - Digitalvoltmeter", model RFT G-1001.500. The roots of this beauty go back to the early eighties as far as I know. I got it as an untested, non working unit from ebay for - hold your breath: 1,00€. Make this 7,90€ delivered - sweeeeeeet. It turns out the device is actually working. Not sure about if it is in spec, but I will find out. What am I talking about?Pic 1: FrontPic 2: SidePic 3: FrontPic 4: FrontPictures 1 to 4 give you an overview what unit I am talking about. This is an classical bench multimeter, Ranges 200mv to 2000V AC and DC, 200µA to 2A AC and DC, 200Ohm to 2MOhm. The Accuracy is pretty impressive. I have to look up the exact numbers, but I think it was about a maximum of 0,5% +/- 1 Digit at all ranges over a common temperatur range.You will immediatly point out the missing knobs and the shabby overall look of this thing, but hey, not even 10€ - what do you expect? I knew that, when I bought it. I think, I will call 'er Miss Piggy.This device was made in the GDR, as you can tell by the shot of the back. One trimpot to reach from the outside and a shielding connector, that is all on the back. On the front only a few knobs and four terminals - what else do you need? Maybe an on-off-switch? You won't find any. We will for sure find out later, why this is the case.There was a hole range of devices made in the same form factor like this unit to form a nice looking, stackable laboratory system.Pic 5: Inventory StickerPic 6: Calibration StickerMy unit was not only build in the former GDR, it was also used there, as you can tell by the calibration and inventorystickers on the sides (Pictures 5 & 6).Pic 7: Detail HandlePic 8: Just for stacking?The handle can be used as standing foot as always. It locks in many positions. Look at the nice metalwork on the spring-mechanism (Picture 7).The feet (can be seen in Picture 3) and plasticpieces on top (Picture 8 ) are not only for stacking, they also alow to open the housing very easily: By giving the screw about one or two turns they loosen up a bit and can be pushed back. Then the top and bottom halves of the case can easily be taken off. A very nice and well working solution.Pic 9: DisplayOf course my beautyful miss Piggy was fired up, and there is a problem. The two last digits have dark elements (Picture 9). The third digit comes on completely after a while, the last one won't. I of course suspect some bad solderjoints there.Pic 10: ManualPic 11: Fold-out-schematicsThe last pictures for today (Pictures 10 & 11) show the manual, a specification sheet and the service manual. I got them as .pdf on a different forum and made them into that little book. This is of course diy (another hobby of mine). I still have the (crappy scanned) .pdfs. If you want them, drop me a line (I was allowed to give them away). And yeeees, there are fold-out-schematics! I like it!If you are interested you can join in when I lift miss Piggys' skirt the next time. Maybe this leads to some nice crusty sovjet electronics porn.Comments are appreciated as always.See you!Click here forPt. 2.1: Topless miss Piggy

author: Vgkid
author_rank: Super Contributor
timestamp: January 10, 2014, 09:25:05 pm
content: I actually like the detail that was spent on making the tilting handle. I really want so see the insides.

author: brabus
author_rank: Frequent Contributor
timestamp: January 10, 2014, 09:34:41 pm
content: Undress her slowly...Great bargain!

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 11, 2014, 02:00:53 pm
content: I told miss Piggy we were going to do some more shootings, and of course - tell a lady she is beautiful and sure enough she is all in. O0Pt. 2.1: Topless miss PiggyBefore you go any further make sure you understand we are going to undress a grandma - maybe a bit odd perhaps. I spent a while browsing through the service manual and found some interesting details: My Manual dates back to 1977! And for sure it was not the first version. It also got some extra sheets with errata. By looking at it I found some for units made starting from fabrication Number 5405, dated back to october 1979. Look at Picture 4 in my last post and see: my model is number 3285, therefore I guess it has to be dated back to around 1978 maybe.I did not expect that...Well, we wanted some vintage porn, right? I will start slowly as suggested with her top, no gentleman will head straight to the panties?Pic 12: Overview with top lid openedPic 13: Detail of clipsThe top cover comes off very easy by turning the four screws in the plastic clips a few times and pushing them to the back. The piece is made of aluminium by the looks and weight of it. The inside is covered with some brown non conductive sheet (Picture 12). Does not feel like plastic, any ideas what we got there?The clips are some cleverly designed and nicely molded plastic parts. They can not rotate out of direction and stay where they belong when the lid is taken of. Nice Detail. Appart from that they seem to be pretty robust and the plastic does not look aged (which goes for any plastic part as far as I can tell).Pic 14: Overview of top PCBI had bad luck with my camera, the batteries are empty, therefore you get only a part of the top PCB and lots of detail shots which I managed to get before it turned off. But take a peak at the full package in Picture 14. You see the parts nice and clearly laid out and can get a look at some sweet details. The dimensions of this board are 22x23 centimeters by the way. I think I will go into the details of this board later. Let us first look at some random detail shots.Pic 15: Detail of beautifully tied down wiringPic 16: Large HeatsinksPic 17:large crystal(or maybecondensator?) It is some kind of Diode!Pic 18: some axial electrolytic capsThe first thing I noticed when I first opened this device was the beautiful work on the wires. No cable straps or metal tabs to keep them in place - they are all tied together neatly and also secured with some cord (Picture 15). As you will see in the following pictures any large part was tied down in the same manner. No gunk, but anything is for sure in its place, no matter how hard you vibrate the lady.Sure enough the large heatsinks are tied down, too (Picture 16). I always liked those round ones, I think they look beautiful.Picture 17 shows what seems to be a crystal oscillator by the looks of it. It may also be a large capacitor or something else. There is no visible marking on it. The partlist lists it as reference element (no word on what kind of reference). There is an overview of connection diagrams, that finally gives a hint. The device is marked with a colordot on the side, indicating a kathode. Type number in the part list is "SZY 23", therefore I guess it is some kind of zenerdiode or something like this. In a metal can? Never saw something like this before.Of course the electrolytics are large in this thing and therefore tied down, too (Picture 18). The insulating foil around them looks a bit odd because it came loose in several spots, but the devices look good. No leaking, no warping so far.Pic 19: Detail of trimpotPic 20: precision thin film resistor in the background and artistically mounted one in frontOn to some resistor pornography. Have you ever had a trimpot with indicator on the side? (Picture 19). Or a resistor mounted like the one in the front in picture 20? It is soldered to some connectors on the pcb with the leads bown into a accurate S-shape. I guess for heatspreading and possibly easy desoldering. Also, the S-shape may help taking out some vibrations, I dont think they really needed the extra lenght in the leads there because they chose larger types for higher power applications whenever needed.In the background is a precision thin film resistor, whatever that meant back in the days. Well it is a 0,5% precision type, not bad at all. And look at its leads: Nice little plastic spacers on them! You find these on many standing parts. There are also Transistors that have nice moulded plastic spacers under them. Attention to detail...Pic 21: SpacerRemember the case is made of aluminium? Not the strongest metal yet. But it surely will not warp in this unit! Look at these nice, non-conductive spacers. (Picture 21) There are two on the top PCB and I know there are two more in the same places on the bottom one. They mount onto an internal structure that helps supporting the PCBs. Therefore they double to screw the PCB in place. You have to know this, else you won't be able to ever take any PCB out of this thing.This is it for today, next on I will show you some detail-shots of some obscure sovjet ICs and the topology of the top PCB. Maybe I will also start to take it out, we will see. Hope you like it! Keep your comments coming, motivates me every timeClick here forPt. 2.2: Topless part porn

author: sync
author_rank: Frequent Contributor
timestamp: January 11, 2014, 02:18:14 pm
content: Quote from: schwarz-brot on January 11, 2014, 02:00:53 pmIt's a temperature compensated zener. The metal can is for hermetical sealing.www.oppermann-electronic.de/assets/applets/szx23a.pdf

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2014, 02:27:33 pm
content: The brown is a phenolic paper resin sheet, used for insulation and damping. Same with the spacers, though those are resin impregnated cotton sheet wound on a former.Sad to say those capacitors, though made in January 1978, are likely to be now in need of replacement. You will have to cut the nice lacing cord used on them and replace them, though for now you could use them but at some point they will fail. Measure ripple voltage across them and it will likely be very high.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 12, 2014, 01:23:32 pm
content: Pt. 2.2: Topless part-pornJust some random shots of the beautiful parts in this device. before I lift out the board in the next post. Too many pictures to get it done in one. If you don't want that many pictures, just say it.Picture 22: electrolytic capPicture 23: more ancient capacitor pornographyPicture 24: Moneyshot of two beatifully lined up rectifier bridgesPicture 25: This fuse is a bit corrodedPicture 26: as promised, some more spacers underneath some transistor cans this timePicture 27: Crude sovjet IC Packages 1: Flip-Flop Type U103DPicture 28: Crude sovjet IC Packages 2: Operational Amplifier Type A109DPicture 29: Crude sovjetICPackages 3: Silicon Diode Type SA403Next part:Pt. 3: Flipping out the PCB

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 12, 2014, 01:55:37 pm
content: Pt. 3: Flipping out the PCBPic 30: Little metal tabs hold the board in placePic 31: rotary joints allow to flip up the boardPic 32: And there it isPic 33: Display PCB directly mounted onto the large PCBIn part 2.1 i mentioned the spacers had to be unscrewed to take out the board. This was wrong, they are directly mounted on the PCB and can stay in place. There are four metal tabs (Picture 30) that hold the board down. I dislike this solution as these tabs tend to brake if you wiggle them too often. But hey, this shouldn't have to be done that many times.When the tabs are open the board rotates in some nice joints in the housing (Picture 31). You have to flip it up 90 degrees to be able to take it out completely, else it will stay in place. This solution is well engineered.To be able to tilt the board to the angle seen in picture 32 some cord has to be cut to give the wires more room. They must be renewed before using this unit again as this ensures the insulation of the metal housing in case of a brogen wire. Now we know, why everything is tied down so neatly.Ontop the large PCB you see the display board (Picture 33). It is mounted with some brackets. No connectors anywhere! Every signal comes to this board with an individual wire...Pic 34: dirty or corroded solderjointsPic 35: eeeew. Dislike! Yes, it is large.Pic 36: possibly some joints were retouched?What does 35 year old sovjet soldering look like? Not so nice... Some joints look really crusty, maybe the ones in Picture 34 are corroded? At least they are far from nice looking. Lots of gunk on the backside of the board. Don't even want to know what that blob in Picture 35 is!Picture 36 shows something that is quite remarkable: There are lots of solderjoints that look a bit greasy, as you would expect after 35 years. But there are nearly as many that look nice and clean. My guess would be this board was reworked some time. Haven't checked the other PCBs yet.But what can I say? All the joints relating to the faulty display element do look like they were not reworked while all the other display-related joints look nice and fresh. I for sure will point my iron there!Pic 37: just for pure amusementNext post will give the schematics of the top board and and overview of the functions.Pt. 4: Schematics of the top PCB

author: Vgkid
author_rank: Super Contributor
timestamp: January 12, 2014, 03:55:32 pm
content: Thanks for posting pics of the internals, I'm surprised to see so much flux on the board.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 12, 2014, 05:55:51 pm
content: I've got a few spare minutes, so on toPt. 4: Schematics of the top PCBPic 38: Partnumber overlay of top PCB (Reference 202)Pic 39: Partnumber overlay of Display PCB (Reference 203)Pictures 38 and 39 give you the partnumbers of any device on the boards, if you want to find them when looking at the schematics. The reference numbers 202 and 203 are the ones given in all documents relating to this unit.Pic 39: roughly indicated sections of the boardPic 40: Schematic power supply (reference: 202 FG5)Pic 41: Schematic A/D Conversion (reference: 202 FG3)Pic 42: Schematic digital output circuitry (reference: 202 FG4) and display board (reference: 203, no FG)Picture 39 gives you again a top view of the top PCB. I roughly indicated the areas dedicated to FG3 to FG5, only for quick reference, don't be too harsh on any part sitting in the wrong section. Pictures 40 to 42 are the schematics of those indicated sections. Please note that the display board seems to be considered as part of the digital output section, although it has an own reference number (but not Section Number!).After that, if you really want to dive in, I give you two .pdfs: The first one being the Parts-list, which is somehow incomplete as it only gives the items that could be ordered to repair this thing. Second is kind of a quality chart ("Qualitaetspass" ==> "quality passport") which gives all the numbers on rated accuracy. May be interesting, but be warned: everything is in German!1: Part Numbers.pdf2: Qualitätspass.pdfThat is it for today with miss Piggy, I don't want any trouble with my real missNext:Pt. 5.1: Lifting the skirt

author: iDevice
author_rank: Regular Contributor
timestamp: January 12, 2014, 07:15:22 pm
content: Quote from: Vgkid on January 12, 2014, 03:55:32 pmLooks like standard tropicalization for that era to me.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: January 13, 2014, 03:54:09 am
content: PIC 20: the S curve in the resistor leads allow it to accommodate thermal expansion from self-heating and move up or down accordion style without inducing as much pressure on the solder joints or resistor body. That would be my guess anyway.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 13, 2014, 03:00:09 pm
content: Hang on guys, miss Piggy is about to get her skirt lifted!Pt. 5.1: Lifting the skirtPic 43: Shielding between top and bottom PCBPic 44: again metal tabs to hold the Board in placePic 45: Shielding removedWhen the top PCB is flipped up you can see on a large sheet of phenolic board underneath (Picture 43). This is obviously not the second PCB but a large shielding board. The copper side is directly connected to ground on the bottom PCB via a short wire. This board is mounted again with some metal tabs (Picture 44). There are six pairs of them. It is easy to remove the board but a pain in the a** to put it back on - trust me! Underneath you won't find anything interesting: Just the backside of the bottom PCB (Picture 45). It is remarkable this side is in way better condition then the top PCB was. The board looks quite clean, even though the mounting side looks as awful as the one on the top PCB did.The Shielding is obviously needed to shield the bottom board against the digital circuitry above it.So, nothing fancy here, time to lift miss Piggys' skirt and take off the bottom half of the case!Pic 46: More Shielding on the mounting side of the bottom PCBPic 47: Again wired to groundPic 48: Bottom PCB without shieldingSo underneath the skirt you will find...... Panties. Of course no lady would leave the house withoutYepp, I am talking of shielding. Picture 46 shows you, what to expect after you open the case. Note the holes in the shield, whit a nice label beside every one. Attention to detail again. The sheet is again wired to ground (Picture 47). I am glad on this side it was mounted with screws. Makes it easy to take off and see inside the can (Picture 48). You get three seperate compartments in there.Pic 49: in the can 1: precision resistors and capsPic 50: in the can 2: laaaaarge capOne compartment takes the extended backs of two range switches ("0,2" and "2"). The next takes some thin film precision resistors and a few small capacitors (Picture 49). In the last one you only find one huge styroflex (is it everywhere called like this?) condensator. Never saw such a big one before (Picture 50)Pic 51: Trimpot for zero compensationPic 52: precision resistive networkSome more random shots. Picture 51 shows the trimpot for zeroing the device if needed. Note the large head they put on there. You won't be able to miss it with your screwdriver. Again, attention to detail. Picture 52 is just a resistive network I found beautiful enough to take a picture of.In the next post I will reveal the secret of the missing powerswitch. Or can you guess by now? Also I will show the main chips on this board.Pt. 5.2: I want her naked!

author: Vgkid
author_rank: Super Contributor
timestamp: January 13, 2014, 03:38:30 pm
content: What is the component in pic 47 marked 28?, it is beside the top smaller metal can. It has what appears 6 leads, dual fet/bjt.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 13, 2014, 03:42:06 pm
content: Quote from: Vgkid on January 13, 2014, 03:38:30 pmIf you look closer.... you've been fooledbtw, I love the detailed pictures!

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 13, 2014, 04:01:57 pm
content: I will give the schematics and the part overlay in one of my next posts when I bring this series to an end. These parts are actually numbers 289 and 290, you cannot see the 9 of the first number. It is twoSC239 (german)in what I think is a current mirror configuration by a quick look at the schematics. It is low noise npn-Transistors. I will take an extra shot of these for my upcoming post.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 13, 2014, 04:20:56 pm
content: Pic 53: Detail transistorsPicture 53 shows the requested transistors. Sorry, I was not allowed to edit and attach this picture to the last post. I hate doubleposting.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 13, 2014, 06:23:59 pm
content: Pt. 5.2: I want her naked!Pic 54: A wire with a partnumber?Pic 55: These are no inductors!Pic 56: More beautiful input networksPic 57: TrimcapsLet me show you some input circuitry. Can you spot the resistor in Picture 54? Yes, this wire has a partnumber, it is actually a 0R1 shunt. This isn't the only shunt, it is actually a ladder construction, adding more shunts when switching through the input ranges. The three large coils in picture 55 are actually resistors! From left to right: 0R9, 9R and 90R, finally a standard thin film resistor with 900R which can be seen on the right.Next we have some reference resistors (partnumber 211 to 218, horizontally lined up) for resistance measurements and a part of the voltage divider (numbers 219 to 231, group of 3x3) in picture 56. Once again only because it looks beautiful.Picture 57 shows some trimcaps. These are the ones to be reached through the holes in the shielding. They are part of a frequency compensated AC voltage divider. This thing measures in the AC ranges accurate over a given frequency range of 45Hz up to 20kHz. Well, only sine, of course.Pic 58: AC Amplification with OPamp Type A109DPic 59: DC Amplification with OPamp Type MAA725CSome fun with operational amplifiers... Most of them are the A109D or B109D types we have seen before. AC amplification is done with a A109D (Picture 58). But take a look at the DC amplification: I rarely saw a metal can with so many legs. Beautiful! This one is Type MAA 725C (Picture 59). I could not find a datasheet for it.Pic 60: Diodes coupled to share the heatPic 61: some more Diodes coupled togetherPic 62: Zenerdiodes bodged onto some capsPic 63: diagram of picture 62All around the board you will find Diodes mounted in a way that allows for temperature coupling. And yes, these are actually diodes in picture 60.In Picture 61 it is a whole bunch of them keeping each other warm.Finally I found a bodge! These Diodes in picture 62 are soldered directly to the legs of the coupling caps. They are mounted in the same holes, but their second pin is soldered together on the fly, there is a hole missing in the PCB. I don't know if there is a pad on the other side. The caps are for coupling the output of the AC-amplifier into the rectifying circuit and bridged by those diodes (Picture 63). I am not sure what is going on there, but it looks like the diodes are purposefully mounted in a way that ensures their case to touch the lead of the capacitor. Maybe this is also some obscure temperature coupling? I don't know what to think of this.But I can tell you they were really serious about anything relating to temperature drift. Follow me through the next pictures to see with your own eyes.Pic 64: One more can to openPic 65: Some foam. What's underneath?Pic 66: one glass tube, two cans, many contacts. Hmmm.Remember this can in Picture 64? I did not forget to open it up. Inside you find mostly some foam (Pictures 65 & 66). And some not so obvious solutions. This is a oven that keeps two FETs at a constant temperature. The glass tube you see is mercury filled, it is a temperature sensor. Better not drop this thing! The FETs are integrated in a metal cube, brass by the looks of it. This cube is heated by a coil that is switched on and off via the mercury tube. The foam insulates this hole package, of course. But I think it also is used for shock absorbing purposes.According to the manual the FETs form a temperature compensated (obviously!) differential amplifier stage that sits in front of the DC amplifier you saw in picture 59. This is supposed to give a high input impedance and minimal offset currents.I am pretty sure, this is the reason for the missing powerswitch. Most of the parts in this device are chosen or tweaked for low drift over temperature. With an oven in a device without any ventholes you would get constantly changing temperatures if you switched it on and off regularly. But if it is always on, it will reach a stable point and stay there while being pretty immune to short-term ambient temperature changes. Not sure if this is exactly the reason, but that is what I suspect is going on there.I will do one final part, hopefully tomorrow, to give you the schematics of this second PCB. Stay tuned.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 13, 2014, 08:21:00 pm
content: How does that mercury tube work? Maybe capacitive, because the mercury will not be able to move freely like in a mercury switch.

author: david77
author_rank: Frequent Contributor
timestamp: January 13, 2014, 09:10:12 pm
content: I suspect it is a kind of mechanical switch. As the mercury column expands it closes a contact and the heater is turnedonoff. I reckon the tiny red and yellow wires go to the switch contacts inside the glass tube.Could be entirely wrong, though

author: Alana
author_rank: Frequent Contributor
timestamp: January 13, 2014, 09:37:36 pm
content: Basically everything that is in modern multimeter but in discrete parts. I'm looking for repair results.

author: Vgkid
author_rank: Super Contributor
timestamp: January 13, 2014, 10:10:37 pm
content: Thanks for the clarification with the dual bjt'shere is some info on the MAA725http://www.amapro.cz/datove_zdroje/katalogy/katalog_tesla/katalog_tesla_57.php

author: anotherlin
author_rank: Frequent Contributor
timestamp: January 14, 2014, 09:13:36 am
content: Really nice !

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 16, 2014, 10:14:31 am
content: Sorry for not posting, folks. I had some very nice hours with my miss Piggy. We even came to the point where the hole Display was working.As I mentioned before I suspected some bad solderjoints to be the problem. I then resoldered everything that is somehow connected to any element in the display: The driver ICs, every resistor, the transistors, every wire and the 7-segment elements themselves.Pic 67: What the display should look likeSure enough, it all worked after that. Look at Picture 67: The only thing photoshopped is the size. Every Element worked, trust me!I then built everything back into its right place, only to find the same elements as before to be not working. WTF?! I grabbed my DMM and started measuring. Every voltage was where it should be, but three of the four related transistors hat a somehow lower BE-Voltage. I ripped them out and replaced them with BC550's I had at hand. All the elements lit up. A bit dim, but they are there. Built in - elements dead. AAAAARGHOk, take a breath. Measure again. Everything is fine, these suckers just do not work as they are intended to do. Checking again, one element came on, another one on another 7-seg died. Came on again a little later. WHY?!Again a soldering-party. Retouched every joint again, resolderd even every single track on the display PCB (No soldermask on there). Turn it on, some random elements dead.I then decided to rebuild the whole wire harness connecting PCB 201 with the Display board. I had seen it was built with solid wires, maybe there were some broken ones? Percussive maintenance would sometimes help to turn on or off a random element. Seemed to be a possible problem. This took me the whole afternoon yesterday. Yes, I tried to bind my wires in the same way it was originally done. Does not even look too bad (pictures will follow later). Good luck I beeped every wire before I ripped them out - the display module is not original! It is not connected in the same way the manual said. The 7-seg-displays are not the ones listed in the part-list. So maybe this is the reason why so many solderjoints seemed to be retouched? Maybe someone had this issue before? But I am sure this was done by someone who knew what he was doing. Well, 40 Wires later - it worked!At least for about a hour. Now its the same as before.I then went a bit crazy and again, with some percussionsome more elements went dead. But this time I pressed directly onto a 7-seg and this element went completely dead after that. But these were resoldered several times by now. I can only suspect the elements being bad themselves or possibly their leads to be corroded and not taking the solder as they should.At the moment I think of rebuilding the hole display-PCB on stripboard. Maybe I should get me a desoldering gun first.That's where I am right now. I cannot simply bodge in some modern 7-segs as the original ones have a very uncommon footprint. They are not only wider than normal while not being very high but also have an unusual pin-arangement. Also, I want to keep the device as original as possible on one hand. On the other, if I start to go crazy with this repair, I am going to replace every electrolytic as well. Hmmmm.For the temperature switch: As far as I could find out it works like a usual merury thermometer. Inside is the mercury on one side, some other compressible stuff on the other. The hotter it gets the more the mercury will expand, taking more room in the tube and eventually reach the switching contact which than gets closed. Please refer to Picture 66:The small red wire goes to the lower contact ring on the glass tube, the yellow one to the upper. Both contacts can be seen on the outside of the tube, the lower as a ring, the other in form of an eight. These Contacts also have a Pin that is embedded in the glass and reaches to the inside of that tube to allow contact with the mercury. On my photo these inner contacts cannot be seen, sorry for that. On the right side one can see a larger cave inside the tube. This is a kind of blast protection: It simply gives more room for the materials inside the tube to compress. This information on general function is taken from anWikipedia article (german only!)In the G-1001.500 this tube is part of a two-point-temperature regulator. The mercury tube is obviously the temperature sensor. It is on one end embedded in a metal block. This has holes for the transistor cans (they can be seen on the left). Also there is a coil on the round part of the metal, connected to the big red and clear wires. All the other wires are for the FETs of course. If the mercury does not reach the contact (that means it is open), the coil will heat up the construction. The large piece of metal gives some thermal mass for speeding down the effects of heating up and cooling down a bit (giving some kind of hysteresis). Then, when the mercury closes the contact, the coil is shut down. The device starts to cool down, eventually open the contact again to restart the cycle. This Switch is built to hold the construction at about 55°C.I especially like the fact that this construction cannot wear out. Very reliably as long as you don't breake the tube. Which is nearly impossible. Just see how it is held in place by the flexible wiring, a drop of glue and completely surrounded with nice soft foam. Even if the PCB brakes it sits safe in its own can with the leads mechanical uncoupled.

author: PA4TIM
author_rank: Super Contributor
timestamp: January 16, 2014, 11:00:38 am
content: That are very good pictures. Some are pure art like the line of rectifiers. What do you use for that (camara, lense and light)

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 16, 2014, 11:39:48 am
content: It is an 2005 vintage Konica Minolta (screw you, SONY!!!) Dynax 7D, also known as Maxxum 7D or Alpha 7Digital, with its 28-100mm cheapy kit-lense that I only use for the pictures covering a larger area as it is just crap. Every detail I shoot with an early nineties 100mm / 1:2.8 AF Macro lense. This is an absolutely perfect lense and I was very lucky to get it for just 200€. Back then these things went for 500€ to 800€ on Ebay. Canon or Nikon would proudly stick this lense into a white body and paint a golden ring on it. Not well suited for portraits though, as you're going to see every single pore in the skin. An what is inside that pore. UrghI use the built in flash and my daylight-coloured bench-lighting.Everything in this topic is shot free hand. I do not own any more equipment as I figured out very soon that this is a pricey hobby and I would not carry such a huge and heavy camera on my motorcycle or while hiking. Since then I always looked at smaller cameras but never really wanted to start again, or when I decided to, had no money for that. What I have is perfect for macro-shots as you see, and this is what I especially like. So maybe I will get me a decent tripod some day and build me a ring-flash. We will see. This is something I like, but for sure no major hobby.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 16, 2014, 12:37:25 pm
content: Thank you for the explanation of the temperature switch. Since the pin beloning to the yellow wire is not visible and the 'strange' figure 8 I thought that it maybe was some kind of capacitive detection. Mystery solved!

author: Vgkid
author_rank: Super Contributor
timestamp: January 16, 2014, 02:43:31 pm
content: Congratulations on getting it running correctly. I found the explenation on the ovenized dual fets to be very enlightening.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: January 17, 2014, 12:40:36 pm
content: Finally I come toPt. 6: Schematics of the bottom PCBPic 67: Partnumber Overlay of Input PCB (Reference 201)Again I give you first the Overlay with the partnumbers for reference. The bottom PCB has reference number 201.Pic 68: Roughly indicated Board sections. Everything not marked is Inputselection, Signalconditioning and analog SignalanalysisPic 69: Schematics of the input section (Reference 201 FG 1)Pic 70: Schematics of the rectifying and averaging circuits (Reference 201 FG 2)Picture 68 gives you an indication of where the single sections can be found. The relating schematics are given in pictures 69 & 70. Note that the functional group FG 2 contains two separate areas on the PCB. Both, rectifying (red) and averaging (green) are for preconditioning the signal for the A/D conversion. The rest of the PCB corresponds to FG1 and does everything related to range and function selection. The signal is routed to the corresponding circuitsections and treated depending on the choices made by the user on the front panel. Every measurement is to be based on a equivalent DC-voltage measurement of a maximum of +/- 2V.Pic 71: Schematics resistance input protection circuit (Reference 214 FG 6Picture 71 gives the schematics of an input protection circuit which is missing in my device. I guess this can be found in later units. It is obviously an extra PCB (Reference 214), and FG 6 indicates it was kind of an afterthought / retouch thing. The Fuse number 35 can be found on the Fuse-PCB and relates to the resistor measurement jacks. Maybe this PCB was exchanged in later units. I don't see much room for an extra PCB elsewhere. Whatsoever, this board is solely dedicated to protect the input circuitry from voltages mistakingly applied during resistance measurements.At this stage the walkthrough is complece, nothing more to mention on this device. I welcome every comment. As I said before, every comment gives lots of motivation and kills the feeling of doing all this work for nothing.Thank you Sync, SeanB, chickenHeadKnob, Vgkid for pointing out some Details and giving helpfull links. And also thank you to everyone else for your kind words!Pic 72: Replaced TransistorsPic 73: 40 wires to solder and bind to a harnessPic 74: the selfmade wireharnessThe last pictures I give you are just for amusement and show my attempts to bring the display to live again as descriebed in an earlier post. The replaced transistors in Picture 72 and the rebuilt wire harness in progress (Picture 73) and completed (Picture 74). I tried to use the same technique as the original wire harness featured as I wanted to try it and also wanted to restore the original look and feel of the device. Not too easy but I managed to get the binding right somehow. If you get used to it it is not even a slower technique than using cable straps. My wire is flexible 0,25mm² which is way bigger than the original wiring but was the smallest I had on hand. Barely fits inAs I said before, maybe I will retouch this thing completely, but this can be done later. I need a well working Bench Multimeter and have another candidate waiting right now: The Philips PM 2422 A. Same era, same ranges and accuracy, but nixie fun. Also seems to be working better. I guess this is a nice candidate for the next teardownSee you,Jan

author: daqq
author_rank: Super Contributor
timestamp: January 17, 2014, 03:00:32 pm
content: Thanks for the very nice teardown so far! I especially liked the temperature switchQuoteIt's Czechoslovakian Tesla's version of the (LM)725 OP AMP. If needed they SHOULD be interchangeable.

author: Vgkid
author_rank: Super Contributor
timestamp: January 17, 2014, 03:05:54 pm
content: Nice job on the wire wrapping.Daqq: Can i safely assume that most Tesla parts have equivalents to Western companies?

author: daqq
author_rank: Super Contributor
timestamp: January 20, 2014, 06:57:35 am
content: QuoteHmm... a lot of the standard stuff (logic, op amps, simple analog, some power (78xx), misc...) has a similar number to an equivalent western device. Transistors had very different numberings, diodes as well AFAIK. They did have special stuff (hybrid devices, precision stuff) that had a special numbering as well.For instance the 74xx series is just MH74xx (optional extra text). The 8080 has its clone in MHB8080A.Now Soviet parts had very different numbers, although a lot of them were pin compatible ( K155?A3 = 7400 ). Mechanically, I've heard that some used a 2.5 mm pitch instead of 2.54 mm. Could be wrong though.

author: Thilo78
author_rank: Regular Contributor
timestamp: May 09, 2014, 11:57:19 am
content: Hey guys,this teardown is really great.I'm looking forward to the delivery of my G-1001.500, which should arrive today or tomorrow.I paid a bit more, but expect a working meter.@schwarz-brot:I read about the missing power button in these units. Do you plan to add one for future use?Or do you leave it on stand-by duty as it was originally designed?Thilo

author: mamalala
author_rank: Unknown
timestamp: May 09, 2014, 05:33:37 pm
content: I could swear i have seen those 7-segment displays for sale as NOS on eBay some while ago. I remember that due to the uncommon way the segments are built (two short segments instead of a single longer one, for each of the seven segments) as well as the pin arrangement. There are tons of old GDR parts floating around out there on various sales channels. Too bad i never bookmark that stuff..Greetings,Chris

author: mamalala
author_rank: Unknown
timestamp: May 09, 2014, 05:41:36 pm
content: Ahh, found some of these displays:http://www.ebay.de/sch/i.html?_odkw=vqb+71&_osacat=0&_from=R40&_nkw=vqb+71&_sacat=0Greetings,ChrisEdit: Just saw that Oppermann has some of these displays as well:http://www.oppermann-electronic.de/html/halbleiter.html(Search for "VQB 71" on that page, 0,95€ per piece)Edit 2: Damn, scratch that. Just saw that in your display-board you have common-anode displays, while the 71 is common cathode...

author: Thilo78
author_rank: Regular Contributor
timestamp: May 10, 2014, 11:04:50 am
content: Chris,thanks for the info anyway.It's always helpful to identify parts of that kind.It seems that VQB71 is the common-cathode numeric display, while VQB73 is the +/- display.Interesting thing here: The parts list posted by schwarz-brot earlier states the VQB71 and 73 for the display.And these are, as far as I could figure out, all specified as common cathode. (source:http://www.mikrocontroller.net/topic/215116)I wonder how this fits together. Going to find out as soon as my G-1001 is hereEdit: Apparently people are not quite sure about the setup. In some Eagle libraries (http://www.mikrocontroller.net/articles/Eagle-Bibliotheken#RFT-Opto_Bauelemente) the VQB71 are stated as common-anode, while the common-cathode displays are referred to as VQB17.Interesting...Does anyone happen to have a copy of the original RFT data sheets?

author: mamalala
author_rank: Unknown
timestamp: May 10, 2014, 02:52:32 pm
content: Quote from: Thilo78 on May 10, 2014, 11:04:50 amYeah, it's all rather strange. In his post where you can see the schematic,https://www.eevblog.com/forum/testgear/vintage-teardown-and-hopefully-repair-rft-g-1001-500-benchmultimeter/msg366706/#msg366706, it is shown as VQB 84 for the digits, and VQB 85 for the +/- sign. But in the partlist in the same post, it is listed as VQB 71/73. Also strange is that there is nothing to find for VQB 84 on the net, at least i couldn't find anything. Also, all the displays in that style that i have seen so far have always been VQB 71...But then i guess it might be worth a try to grab some of these displays and try them. If it doesn't work one would still have some rather curious display type for some project... Or maybe the U121D's have enough drive strength to drive the displays directly. In that case just bypass the transistors and change the former base resistors...Greetings,ChrisEdit: But then, who knows, maybe they thought "Damn those imperialists, we'll show them and swap the meaning for anode and cathode!" :-D After all, IIRC the pin pitch on old GDR IC's/headers is 2.5mm instead of 2.54mm. At least i had that experience a few times, when the standard 0.1" spacing turned out to be just a tad too much after 10 or so pins...

author: Thilo78
author_rank: Regular Contributor
timestamp: May 10, 2014, 04:03:49 pm
content: The pin pitch topic is quite common with eastern tech.Especially the 2.5 mm pitch ist quite common, apparently.btw: As for the wire bonding I can top that with my today's arrival:The Meratronik Electronic Multimeter U726, made in Poland in 1976 (thus two years older than me).I popped it open, as it's missing the power cord, which would attach to a strange DIN-like socket. So I replaced the socket with a nice fabric-clad lead, and added a more solid earth connection to the aluminium case.They made the internal wire harness from solid wire, bound with blank wire. Looks neat.I'll see top post the pics as soon as I have downloaded them.Works fine, but I'll need to do some adjustments. The 30V range seems quite off.That will certainly help me pass time until the G-1001.500 arrives.

author: FrankenPC
author_rank: Unknown
timestamp: May 11, 2014, 12:27:25 am
content: Too bad you can't apply a patina to the replaced transistors.

author: Thilo78
author_rank: Regular Contributor
timestamp: May 12, 2014, 02:14:54 pm
content: Aaaand.... here is my part in this game:My very own G-1001.500 arrived today, only minutes after I harrassed the seller about a maybe lost packageShame on me for my impatienceAlthough I did not do an extensive teardown like schwarz-brot did, I have some pics for comparison.I think it's very close to mint condition, except some scars on the front buttons and a few scratches on the covers.And: It came with some goodies

author: Thilo78
author_rank: Regular Contributor
timestamp: May 12, 2014, 02:15:57 pm
content: The goodies:Spare VQB71 display units!And some more pics...

author: Thilo78
author_rank: Regular Contributor
timestamp: May 12, 2014, 02:17:12 pm
content: I powered it up and set my power supply to just about 5 V DC. The U729 is hooked up in parallel for comparison.Please note: The seller informed me, that the G-1001.500 has recently been calibrated. So it shows that the U729 is quite good for its stateOnly problem: One of the fuses is already quite corroded. I'll see to replace it asap.btw: I just noticed, that it's exactly the same fuse as with schwarz-brot's unit. Interesting...

author: mamalala
author_rank: Unknown
timestamp: May 12, 2014, 08:35:49 pm
content: Congratulations, it really looks like almost new.Still wondering about the VBQ 71's... Are they common anode or cathode, and are the ones in the unit really 71's as per the parts list, or 84's, as per the schematic? Another thing occured to me. It's no secret that east Germany had to make do with what they could get/make. Maybe there are indeed different variants of the overall display/drive electronics for this meter, for two different types of displays? Like, ran out of one type? Do the other version with the other type. Just a wild guess.Greetings,Chris

author: schwarz-brot
author_rank: Regular Contributor
timestamp: May 13, 2014, 02:57:27 pm
content: Chris,the G1001.500 was produced in reasonable volume over a long period of time. The documents I linked in are actually for different versions of this meter. The circuits got updated from time to time. The Service manual gives some hints about differences (kind of errata...) but not enough to tell exactly what was changed when.

author: Thilo78
author_rank: Regular Contributor
timestamp: May 13, 2014, 08:29:36 pm
content: Quote from: mamalala on May 12, 2014, 08:35:49 pmThanks! That was quite a catch, and I'm happy to have it on my desk.I'm quite sure, that schwarz-brot's unit will look similar when he's finished with his setupQuote from: mamalala on May 12, 2014, 08:35:49 pmI'm still wondering myself.There seems to be but one option: Pop it open and measure the voltages at the display unit...Not too happy with this approach, but maybe I'll find a way to figure it out without shorting the VQBs.But about one thing I'm quite sure as of my experience with German equipment of the era before 1990:Those guys knew exactly what they are doing. If they have chosen one way or another, there's a good reason behind it, although we as "modern" engineers might have a hard time understanding it.Material availability has always been a common issue, from the 50s through to the 90s, and they always have found clever ways for serial production of reliable gear. (that's confirmed by what I've learned from my father, who headed a development department with Philips' Process and Machinery Automation section, and his colleagues)I'm curious what I'll find while inspecting my newtoystools

author: Thilo78
author_rank: Regular Contributor
timestamp: May 14, 2014, 12:46:44 pm
content: OK, I have done some measurements on the G-1001.I figured out, that the reference point 7 (see schematic) is about ground potential, named Cp.Given that, the upper rail for the LEDs is supposed to be at +7.5 V, and reads between 7.0 and 8.0 V with my Fluke 1587.I'll take that as good level.Further on, this level shows up on the common point of the LEDs.Interestingly, the LEDs show a voltage drop of close to 3 V, which seems quite a bit from my point of view.We'll have to investigate that further, I think, unless somebody manages to find data sheet.As a conclusion I'd say that at least my unit features a proper common anode configuration.

author: mamalala
author_rank: Unknown
timestamp: May 14, 2014, 02:01:57 pm
content: Quote from: Thilo78 on May 14, 2014, 12:46:44 pmSince each segment is made out of two smaller segments, i guess that these are in series, and thus you have 2 times Vf as drop.Have you looked at the spare VQB 71's that you got? Are they common anode as well, or are they common cathode, as the image there in µC.net says?Greetings,Chris

author: Thilo78
author_rank: Regular Contributor
timestamp: May 14, 2014, 02:32:56 pm
content: Quote from: mamalala on May 14, 2014, 02:01:57 pmYes, I have in the meantime.It's a little bit fiddly, as the display are quite fragile without any supporting structure like a PCB.Modern displays are a bit more sturdy due to the shorter leads.I hooked one up with 5 V DC over a 380 Ohms resistor to the central contact, which I suspected to be the common anode.When touching the segment lead with a grounded clip, the segment lights up nice and bright.Doing it the other way round showed no result.So, it has to be common anode.Trial and error shows that half of the data sheets I found are wrongOr (which is possible) they changed the specs over the time, keeping the part number.Like: "What the heck? The old ones sold out. Let's do it the other way round for the lulz!"Edit:Quote from: mamalala on May 14, 2014, 02:01:57 pmYep, seems to be the answer. All segments are actually two LEDs.Open questions:>What is the actual difference between VQB71 and VQB84?Judging from the schematics, they're compatible/exchangable.>Why are there tables stating the VQB71 to be common cathode?

author: Thilo78
author_rank: Regular Contributor
timestamp: May 14, 2014, 02:50:44 pm
content: I just found another site, which appears to be rather reliable:http://www-user.tu-chemnitz.de/~heha/bastelecke/Konsumg%C3%BCter-Bastelei/DDR-Halbleiter/The page is hosted by Technical University Chemnitz and collects technical data of GDR semiconductors.For VQB71 it has this data sheet:It says Common Anode there...The label "Nicht für Neuentwicklungen" means something like "not suitable for new design".Maybe the VBQ71 has been discontinued and replaced by the VQB84...I also just found out what purpose the single VQA12 serves: It's an additional decimal point next to the algebraic sign, used for the 0.2 V/mA/kOhm rangeInteresting UI concept.

author: Thilo78
author_rank: Regular Contributor
timestamp: May 15, 2014, 12:34:15 pm
content: Quote from: schwarz-brot on January 11, 2014, 02:00:53 pmHey, I completely missed that question which seems to be unanswered.I'd think that this is a layer of Pertinax, an insulation material similar to Bakelite.It's a composite of phenolic resin and paper, and it's a predecessor of current FR4 material (which replaces the paper by glass fibre and the phenolic resin by epoxy resin)I don't know if there's a proper English name of that, but I found something like "synthetic resin bonded paper" or "SRBP"It was used for insulation layers like here, for separations within measuring or power equipment, and for circuit boards.

author: hli
author_rank: Frequent Contributor
timestamp: May 15, 2014, 05:14:28 pm
content: Quote from: Thilo78 on May 14, 2014, 02:50:44 pmThe site says that, but the data sheet clearly shows the common cathodes (K1 and K2). I think I have four at home (in an ADC setup which might quite as old as this meter...). So when I'm back home at the weekend, I will try to look at them more closely.

author: Thilo78
author_rank: Regular Contributor
timestamp: May 15, 2014, 05:20:07 pm
content: Quote from: hli on May 15, 2014, 05:14:28 pmNo, I fell for that one at first, as well.K1 and K2 are described as Anodes underneath the sectional view.A..H are the Cathodes as per the pic.That I could confirm by measurement on the units in the G-1001.500 and the VQB71 I have as spares.QuoteThat sounds great. Let me know the result

author: hli
author_rank: Frequent Contributor
timestamp: May 15, 2014, 05:29:58 pm
content: Btw: as far as I can tell from the images, there are no russian ICs or packages in there. Everything seems to be made in the former GDR, with some parts from Tesla in Czechoslovakia (like the MAA725). The A109 is the east german version of the uA709. All the ICs named D1xx are 74xx parts, following the same naming schema.For most of the discrete components, use this cross-reference:http://www-user.tu-chemnitz.de/~heha/bastelecke/Konsumg%C3%BCter-Bastelei/DDR-Halbleiter/to find out what the equivalent is. For smaller transistors, the first letter is missing on the package (so the transistors on #53 are SC239E). The diodes sometimes have just a color code on their top. The date code is typically just a letter-number combination (in #53 looks like a K8 or K9). Zener diodes have the voltage on them, and the date code below.Also, the company where schwarz-brots unit comes from was manufacturing industrial ceramic stuff, including resistors (seehttp://www.robotrontechnik.de/html/standorte/kwh.htm). Some of the resistors in this DMM actually come from there! (as can be seen by the logos on them)

author: hli
author_rank: Frequent Contributor
timestamp: May 15, 2014, 05:31:23 pm
content: Quote from: Thilo78 on May 15, 2014, 05:20:07 pmOh you're right. Datasheets don't lie, except when they do

author: Thilo78
author_rank: Regular Contributor
timestamp: May 15, 2014, 05:44:59 pm
content: Quote from: hli on May 15, 2014, 05:31:23 pmAt least measurements don't lie.Those I did yesterday confirm the (latest) version I quoted here.So I wondered about K1/K2 being anodes, but that was okay for me as it's backed with measurements.

author: Thilo78
author_rank: Regular Contributor
timestamp: March 19, 2016, 08:03:40 pm
content: Any news about the G-1001?Mine is doing well. I only had to replace one of the 7-segment-displays. (the right-most)

author: kblue
author_rank: Regular Contributor
timestamp: September 28, 2024, 03:09:42 pm
content: Gonna use this "old" topic, because pictures and schematics already exist here. I have two of these units - one works 100% fine, the second one has some burned shunts, resistors and shorted caps. Shunts are already replaced as are the caps (except the filtercaps which seems to be fine), meter does "work" in most ranges perfectly fine. While checking parameters from the service manual, the manual wishes for 0 Volts between "LO" (shorted together with HI) and RX2 Input. The fully working G-1001.500 only shows about 4-10 mV at worst, but the second unit shows 0,5 V from start slowly rising to about 0,8 and sometimes close to 1 Volt.The basics don't seem to be affected ... 1 Volt DC is 1,000 VDC, 1k Ohm precision resistor shows as 1k, 1 mA is 1 mA and 1 VAC (1kHz/Sine) shows as 1 VAC in AC-Mode. So i guess it kinda works, but still the book wants 0 Volts between LO/HI and RX2 Input-Terminals. R287 does change the measured voltage between LO and Rx2 (as stated in the manual) but the "Zero @display" will be way off scale. Right now display is perfectly zeroed and any change with R287 (which should be used to lower the voltage between LO/HI and Rx2 throws of the ZERO). I wonder if this is "from factory" and they just "compensated" for it further down the line.So in short: If i change R287, R276 or R277 i could achieve "0 Volts" between Hi/Lo and Rx2 Inputs but the Zero will be waaaaaay off.Best wishes!By the way, my unit has original Nippon-Chemicon filtercaps and HP-parts build in and it seems this was done "from factory" even with sanctions in place in the old days.

author: kblue
author_rank: Regular Contributor
timestamp: September 29, 2024, 02:18:31 pm
content: Problem solved. The round about 0,7 - 0,8 Volts at Position 104 (Emitter of 323) are CORRECT. But die direct connection to Rx2 (Input) wasn't. I checked the cables with another working G-1001.500 and there was some mismatch with the cables on top of the Ohms-Switch. Rx2 isnt supposed to be connected directly to the Emitter of 323, even though it was in my unit. Now the Input (Rx2) is connected where it should be and everything is working just fine. No 0,7V any longer between Hi/Lo and Rx2.

author: kblue
author_rank: Regular Contributor
timestamp: January 02, 2025, 05:11:39 pm
content: ... aaaand back again! With another unit.Everything works fine, but the unit has one unusual "problem". It does not want to "settle" at all ranges. The last digit is always "bouncing". Range or function does not matter ... it bounces gradually at 200 mV or 200 V, or in 0,2k to 2000k Ohms-Range, Amps etc.The "frequency" or up and down of changes seems to be always the same ... like a "sine-wave" so to say. Already tried to heat up some sectors of both PCBs with no change in behavior.All caps, except the big blue filter caps, are already changed and switches cleaned with specialized contact cleaner (not WD40). It's not a "end of the world"-kinda problem but would be nice to have it stable at zero with shorted plugs - as are the other units i have. The slowly bouncing signal is already present before it goes into the digital section, so it's definitely "generated" somewhere in the analog part. Mayhaps giving the board a good wash may solve the problem? Hmm.Lucky me i have multiple units, so i could try to look for differences in the path.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: January 02, 2025, 08:12:43 pm
content: Thanks to all the lucky guys that are blessed to have such gorgeous equipment. The craftsmanship is phenomenal with such great attention to detail. Thank you for sharing.

author: kblue
author_rank: Regular Contributor
timestamp: January 02, 2025, 10:19:28 pm
content: Trying to trace this "up and down" backwards during Mode: VDC Range: 0,2 VNot finished yet.

author: bborisov567
author_rank: Regular Contributor
timestamp: March 20, 2025, 12:52:28 pm
content: Does anybody know what is the current rating of T35 and if it is a regular fuse(it has a slightly different symbol on the schematic compared to the power supply fuses? I have the same unit and there is noting in the place of T35. Could it be a 35 mA fuse?

author: hli
author_rank: Frequent Contributor
timestamp: March 21, 2025, 01:10:15 pm
content: Quote from: bborisov567 on March 20, 2025, 12:52:28 pmLooking at where it is located, and googling in German forums for "T35": yes, I think so. No idea why it has a different symbol - might be a different form factor compared to the PSU fuses (e.g. a non-replaceable part). btw: 'T' means 'slow blow'.