From: Hendrik Dietrich <[email protected]>
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
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