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 :-)
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