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
|
