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 re****t.
>>> 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 ****ny. 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 ****ny 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
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