[Chuck]

On Fri, 18 Apr 2008 08:03:07 -0500, jakdedert
wrote:

RuF wrote:
RuF wrote:
jakdedert wrote:
RuF wrote:

If those measurements were made with the turntable in the off
position, then you are measuring what should be a near short across
the cables. If that is so, then you likely have a dirty muting
switch or bad cables. If that measurement was made with the unit
on and the arm above the record, then you've got the lowest
resistance measurement I've ever heard of on a cartridge.

Regards,
Tim Schwartz
Bristol Electronics

Thanks again Tim. Your help is much appreciated.

This time the measurements were made with the pickup on the record
about
mid point in the tracks.

The results of the measurements were exactly the same as before,
which would
appear to suggest that there may be a problem with the mute switch.
The RCA
cables were installed a few months ago to replace the old 5-pin DIN
plug and cable
and were soldered to the same connections that were used previously.
The original
ground cables from the turntable are still used and are attached to
the chassis
of the Sony amplifier. The ground from the arm wiring is also
attached to the same
wires. I guess I could replace the original ground cables, if
necessary.

Today I'll check the muting switch and clean up the terminals and
anything else I
can see in that area.

I think you definitely should check that area. There should be a
difference in reading with the arm down.

Are you sure you're reading the correct scale on your ohm meter? I
couldn't remember typical DC resistances off the top of my head, so I
pulled out a few old carts and got out the meter. On an assortment
of Shure, Stanton and Pickering units (about five altogether), the
readings ran anywhere from 1.25 to 1.5 *KILO* ohms. However, before
I looked closely at the range indicator on my autoranging meter, I
started to wonder what Tim was referring to.

There's no way you could get any output at all if your cartridge was
shorted out, which is the appearance of the readings you report.
Check again.

OTOH, you should be reading a dead short with the mute switch closed.
Perhaps there's enough resistance in the wiring to give you a reading
of 1.35 ohms--close enough--and the cart resistance is close to that
reading, but in KILO ohms, and you didn't notice the difference?

In the same drawer, which I've not pulled out in years, there are
three NOS (never used--no idea why I have them unless it was from my
days as a turntable setup tech in the 70's) Dual slide-in cartridge
mounts. The contacts on all of those are pretty nasty. IMO, it
would take chemicals or some serious elbow grease to make them
serviceable. I'd pull yours and make doubly sure that all the
contacts, including the ones on the cartridge terminals and the
tonearm, are impeccably bright and shiny. There's a lot of potential
for contact resistance there.

jak


Thanks Jak.

I just completed an inspection and decided to resolder all 4 contacts
on the
RCA cables and the grounds, where they connect into the mute switch area.
I couldn't tell very much about that switch, so I put everything back
together
again and both channels worked for about 15 mins and then the right
one died
way back to less than 10% of the left channel and stayed there looking
almost
dead - just an occasional tiny spurt.

In what seems to be the mute switch there is little block - about 3/4"
square and
about 3/8" wide made up of layers of plastic and metal. It is into
this block that
all 4 connections mentioned above are made. There are also two sprung
contacts
from it that lie against the large plastic wheel with the small gears.
This wheel is
concentric with the platter. Are those two contacts the mute switch?
How could
I disable it for a short while to test further.

The instrument I used was a GB Instruments GMT-12A and the right end
of the
scale has an omega. Then the numbers go 1,2,3 etc .... up to 1K.
Beyond that
is the infinity symbol.

The contacts at the end of the arm are shiny silver but the ones at
the end of the
shell, that make contact with them, are rather dull. I'll try a little
metal polish on
them soon and will let you know what happens.

Have a great evening :-)

I used metal polish to burnish the 4 contacts at the rear of the shell
and then ttried to clean up the 4 mating contacts at the front of the arm.
That was when I noticed that the contacts were embedded in what
looked like a thin plastic sheet. While cleaning, the plate kept moving up
and down. It was just pushed up into a slot and was kept in place by
the shell. I pushed it all the way up and then attached the cartridge.

On startup I had both channels working great. Fingers crossed :-)

Thanks to all for the help.

RuF


Cool, I composed a lengthy tutorial last evening, but realized I wasn't
all that familiar with the innards of the Dual. I got sidetracked
trying to download a manual from this
http://www.vinylengine.com/news.shtml site; but couldn't get
registered (confirming email not sent).

I was skeptical as to whether the muting switch was your problem, but
not familiar enough with the Dual guts to advise. From your post, it's
not directly actuated by moving the tonearm, which would make some of
the advice given spurious.

You have an analog meter, which negated my 'ranging' scenario somewhat;
unless you are unfamiliar with the function of the 'Range' switch on
your meter.

Glad you got it...hope it stays 'got'. I did think it was a headshell
contact issue....

jak


These Duals didn't have a mute switch problem unless the switch assy.
bracket's screws loosened up. There was a constant problem with the
headshell and arm contacts causing muted sound on either channel. As
other posters mentioned, the rca cables were a major failure point.
Another fairly common problem was the wires in the tone arm would go
intermittent. Replacing these isn't a project for the inexperienced.
Chuck