Exhuasted my knowledge on repair, any help?

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Trilogy
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Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 08:40

Vintage Kenwood 8100 amp;fine condition
Vintage KW tuner; fine condition
Sound Shaper Equalizer: FC
Vintage Technics SL-3200 TT. Problem
Bose 801 studio monitors good cond.

All amplifier outputs work. Tuner exhibits two channels .

I only have the left channel working on the TT. I can plug the turntables left channel rca into any one of the four speaker inputs (a-left and a-right, b-left and b-right) and I have good audio output to all elective speakers. The TT’s right rca will not produce audio in any of the 4 speaker options.

I put a DMM set on continuity with alarm on all the respective leads at the shell head and then touched the coinciding RCA pins and collars. Continuity was confirmed in all audio wires from shell to RCA terminals. This suggests to me that the wiring is good from the shell head right through the tone arm harness and on into the Soldered connections for all four wires forming left and right channels and also good beyond that to the RCA pins and collars.

I have tried three different cartriges, (Pickering XV-15, Ortofon FF15XE and Yamaha CG-66) and nothing changes.

The left TT channel plays in any position and the right will NOT play in ANY position . The tuner’s left and right channels through the amp work perfectly.

It’s leading me to believe I have lost the right channel audio somewhere in the TT but the wiring from headshell to RCA jacks all show continuity.

Would anyone please offer their thoughts as to what I’m missing or relate any similiar experience they might have to explain this problem. Sorry for the long post as I wanted to offer as much info as I could. If you need further detail I’ll happily reply. Thank you.

Spinner45
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Re: Exhuasted my knowledge on repair, any help?

Post by Spinner45 » 12 Feb 2019 08:59

So, you've also confirmed at the RCA plugs continuity - an "ohms" reading from the cartridge?
Should be a couple hundred ohms or so.
If not, the cartridge wires in the headshell are defective.

KentT
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Re: Exhuasted my knowledge on repair, any help?

Post by KentT » 12 Feb 2019 14:35

The last post is a great place to begin. Headshell wires also are cheap enough to replace easily on most standard headshells. Also, cleaning your headshell contacts where it goes into the tonearm (and the receptacle contacts) with good contact cleaner is not a bad idea. When dirty they can also cause a channel to not work.

toaster999
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Re: Exhuasted my knowledge on repair, any help?

Post by toaster999 » 12 Feb 2019 15:25

Phono stage in the amp gone kaput?

Alec124c41
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Re: Exhuasted my knowledge on repair, any help?

Post by Alec124c41 » 12 Feb 2019 16:20

Remove the headshell, and check the continuity between the pin and skirt of the RCA plug. There should be none.
My guess would be deteriorated/broken internal insulation behind the RCA plug, causing a short, and curable by cutting the cables back a couple of inches, and installing new plugs, or replacing the cables entirely.

Cheers,
Alec

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 17:02

Thank you Spinner 45. I did not measure the obms through each of the four wires from cartridge to rca jacks. I will do that and report back with findings. Greatful for your advice.

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 17:06

Hi KentT. I will get an aerosol cleaner and use some quetips to clean where I can. Appreciate your help.

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 17:21

Greetings Toaster999. Thanks for your reply. My Kenwood 7100 amp has two phono options; phone one and phone two.
Each of those has the typical left and right channel.

I can plug the left RCA jack from the TT into any one of those four phono options and it will produce sound at the related speaker. I do have to select the particular phono 1 or 2 on the switch on the front of the amp to coincide with where I have inserted the left leaf obviously.
Whereas the right RCA from the TT will not produce in any of the four jacks with the coinciding phono selection made st the front selection switch .

I may be wrong however doesn’t the description above effectively confirm the amp phono outputs are both ok?

Appreciate your thoughts.

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 17:46

Hi Alec124c41, thank you. I will use the DMM to check for shorts within the RCA cables and jacks with the continuity function.

Would you please read my reply to Toaster999 listed above and see if my logic is correct in eliminating the amp as the problems source .

I’m afraid stereo electonics is not my strongest point however I am able to understand any direction given by those that are more up to speed.

The stereo components I listed in my first post were all purchased by me in 1978...41 years ago! They have been cared for very well and have all original packaging and user manuals . Condition wise I’d say excellent, appearance almost as new. I really appreciate the quality of construction, the wonderful feel of the switch’s and controls . Just can’t find stuff like this anymore . The amp went into a shop about ten years ago for a complete check and refurbishment. I just pulled it all out after about 8 years of storage in original packaging in a dry, cool place. No indication of moisture or corrosion anywhere.

When you’ve had these things for so long and cared for them well they are like an old friend as opposed to a yard sale find two weeks ago. Lol.

Thanks to you all for helping. I’d really like to think I can isolate the issue as it is so consistent and so specific .

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Re: Exhuasted my knowledge on repair, any help?

Post by tom6to1 » 12 Feb 2019 18:28

Sounds like you have isolated the problem to the turntable, somewhere between the cartridge and the RCA plugs. If you can, replace components and try again. I know that can get expensive if you don't have spares - spare cartridge, spare headshell, spare headshell wires (good suggestion from another post - do that first as it is likely the least expensive if you don't have other spares). Doing all of this will eliminate that end of the turntable, or identify that end of the turntable, as the source of your problems. Good advise on corrosion/oxidation of the pins and headshell wires. If all the above doesn't find it, Alec likely has it - replace / fix the RCA cables at the plug. Good luck.

Alec124c41
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Re: Exhuasted my knowledge on repair, any help?

Post by Alec124c41 » 12 Feb 2019 20:07

Your left channel cable works with all phono inputs, so the problem is in the turntable.
You have tried different cartridges, so the problem is not there.
You have continuity in all circuits.
A short is all that is left.
If the shirt of the right RCA plug is not tight, it might explain this. It should not slide on easily. Pinch it, if it does.

Cheers,
Alec

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 20:30

tom6to1 wrote:
12 Feb 2019 18:28
Sounds like you have isolated the problem to the turntable, somewhere between the cartridge and the RCA plugs. If you can, replace components and try again. I know that can get expensive if you don't have spares - spare cartridge, spare headshell, spare headshell wires (good suggestion from another post - do that first as it is likely the least expensive if you don't have other spares). Doing all of this will eliminate that end of the turntable, or identify that end of the turntable, as the source of your problems. Good advise on corrosion/oxidation of the pins and headshell wires. If all the above doesn't find it, Alec likely has it - replace / fix the RCA cables at the plug. Good luck.
Thanks for chiming in tom6to1. Your suggestions like all the others are good. I'm on my home pc now so its easier to type concise replies.
I have 3 cartridges that I have tried and the right channel output failure persists.
I have another turntable (Yamaha) however it currently has no drive belt and I haven't located one as of yet so I cant use it as a test unit.

Everyone that has commented, including you and Alec, leans towards faulty RCA cables. I have done some more DMM testing as suggested by you all and will post the interesting results. Hats off to all of you for the generous sharing of experience.

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 20:56

Alec124c41 wrote:
12 Feb 2019 20:07
Your left channel cable works with all phono inputs, so the problem is in the turntable.
You have tried different cartridges, so the problem is not there.
You have continuity in all circuits.
A short is all that is left.
If the shirt of the right RCA plug is not tight, it might explain this. It should not slide on easily. Pinch it, if it does.

Cheers,
Alec
Hearing it written so concisely really instills confidence that I'm narrowing it down. I've done some more testing with the DMM and the results are as follows:

Headshell white lead to RCA white pin------- 3.1 ohms
" " to RCA white skirt------ open

Headshell blue lead to RCA white pin------open
" " to RCA white skirt-------1.8 ohms

Headshell red lead to RCA red pin-----1.9 ohms
" " to RCA red skirt-----open

Headshell green lead to RCA red pin----open
" " to RCA red Skirt----- Intermittent open/high resistance, 400-500 ohms,sometimes low ohms ,

So it appears the right RCA jack has a faulty connection at the plastic molded body. I can manipulate it and the ohms reading varies and occasionally loses all continuity. I have some spare RCA cables so I will check a few for serviceability and splice a new one on to replace the existing faulty right (red) RCA jack.

Having little experience troubleshooting this sort of thing I never really expected a molded jack to fail. I understand now that there will be a fine soldered connection in there that if it had any discrepancies from manufacture it could fail after many years. I guess its a good reminder to grasp and handle them properly when inserting and removing.

Like I said I think you all leaned towards this as a possible cause...pretty fart smellows.

I'm not confident enough with my soldering to attempt to replace the entire RCA at the circuit board so I will splice a replacement on for now and see if it fixes the problem. Will report back. Thanks.

Trilogy
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Re: Exhuasted my knowledge on repair, any help?

Post by Trilogy » 12 Feb 2019 22:27

Fixed!

Grateful to Spinner45, Kent T, Toaster999, Alec124c41 and Tom6to1.

Right channel phono output RCA jack replaced and all systems go. Feels really good to have isolated the problem and repaired it without so much as leaving my living room or spending a dollar.

I was lucky in that it was a simple problem not involving circuitry and easy to repair. The circuitry is out of my league...for now anyways. Lends testament to the quality of these vintage components.

Alec124c41
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Re: Exhuasted my knowledge on repair, any help?

Post by Alec124c41 » 12 Feb 2019 23:17

Love the cheap fix.
That is one of the most common faults. A receiver gets pushed back against the wall, and the cables get bent sharply.
Glad you got it working.

Cheers,
Alec

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