From: Hendrik Dietrich <don_hendi@gmx.de> > Subject: [volt-nuts] Dekavider DV411 repair and question > > Hi List, > > I partially fixed a "lowly" DV411 Dekavider from the > "Electro-Measurements" epoque and wanted to report what worked out and > what still is and have a general question about such devices. > The part in question (just look what the cheapest one on ebay was, one > made a power supply out of it) had a working first and second decade, > but the can with the 3rd switch and last decade potentiometer required > some work. > > The switch freewheeled, it didn't lock onto the right on-digit > position. That was due to the slotted wheel slipping on the drive > shaft out of position so it was no longer pressed against the > spring-loaded ball. I was surprised that this wheel was just soldered > to the drive shaft, so it was enough to push it back into the right > position and solder it down with some very agressive flux (Soldeen-1). > http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=locking_cogwheel.jpg > > > The 4th(5th) decade potentiometer seems to be electrically okay, but > it turns 360? instead of 270?, I consider that it had some delimiters > but these are scraped off. However, careful operation will be > possible or replacement by a potentiometer and a adapter between the > thin driveshaft of the switch to the axle of a new potentiometer. > (Hoped to keep it original.) > http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=potentiometer.jpg > > For Pronographic reasons, a overview is available too. > http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=overview.jpg > > > Besides hints for further repair, does someone know which alloy is > used for wiring by ESI? Seems a bit hard for plain cooper. > > Best regards, > > Hendrik > Hendrik, It's been more than a few years since I had my hands on one of these boxes, but I aeem to remember that the vernier potentiometers in these instruments are designed to rotate a full 360 deg. I don't know why; seems illogical, but that's the way they are. If the original pot works, I wouldn't bother changing it. It will be extremely hard to find a replacement pot with the low tempco that the original pot has. The wire used to make the resistors in these units is probably Manganin, an extremely low tempco compound. Manganin wire has been used by instrument manufacturers for many years for temperature stable resistors. I think that most lab standard resistors are made with Manganin wire, and thermally insulated from the outside world to maintain their accuracy. Dave M

To everybode who answered: Thanks, so it was not only me not finding the leftovers of delimiters. Still curious why they made it that way. No reason to replace! Dave: I am aware of the resistor wire alloys like Konstantan, Manganin, Isabellin, Evanohm and their variants. What I didnt understand yet is the wiring between the resistors and the decades and so on - its just not simple silver-coated or tinned cooper wire, it more looks like a resistive wire - big and massive, bad to solder. Bill: Do I understand right, they use the inter-resistor wiring to for compensation ? (Your mail worked fine) Sounds like a "bigger but reproducable resistance than wildly drifting cooper wire" scheme to me. I try to figure out. The repair itself worked out very nice, the workplace 34401A in dcv:dcv ratio mode was happy with the results. BR Hendrik