Akai AP 103c - call for help..

[pathakajit]

I have been working on bringing up to scratch an old Akai AP103c fully automatic TT.

When I got the TT, it was in a sorry cosmetic condition. The plinth had suffered water damage and was crumbling (particle wood), covering vinyl was peeling off aluminum bits were oxidized and black (literally), dust cover though working was completely scuffed and absolutely opaque. Belt was missing.

It has been a labour of love de-gunking, degreasing, and generally restoring the machine.

The TT is quite a looker and has turned out to my satisfaction. Received the replacement belt (flat, medium, 25.0 inches) today from TurntableNeedles; fittrd belt and fired the baby up. The TT mechanism all seems to be working as expected.

I am however getting very weak output on the right channel. De-oxidized the rca jacks, tried different amp - no joy. Tried same headshell assembly on different TT - works well. Left channel sound level is good. Opened the TT and checked the rca cable solders are thick, strong and shiny. Did not see any bulging caps which may need replacing..
Any suggestions as to what may be wrong?

Disclaimer - while my DIY skills are at least average, my electronic abilities are very, very limited.

Close up of the PCB

Plinth repaired, all linkages degunked and greased

Got new acrylic dustcover fabricated. Original was light brown in color.

All aluminum bits deoxed and polished

The outcome

 

[greenhorn]

looks like you need to do a fairly straightforward continuity check with a multimeter. From the pins inside the tonearm which connect to the headshell to the PCB (to check tonearm wire continuity) and from the base of the PCB to the RCA outputs. Do this for all wires.

If they all pass continuity, measure resistance of the paths in ohm mode, and find if one of them is a bit high. Also check if there is any shorting between any channels

 

[pathakajit]

looks like you need to do a fairly straightforward continuity check with a multimeter. From the pins inside the tonearm which connect to the headshell to the PCB (to check tonearm wire continuity) and from the base of the PCB to the RCA outputs. Do this for all wires.

If they all pass continuity, measure resistance of the paths in ohm mode, and find if one of them is a bit high. Also check if there is any shorting between any channels

Thanks, Greenhorn.
Will arrange for a DMM and check the paths today.

 

[greenhorn]

I see two sets of wires going from the pcb. One of them to the RCA, but what about the other one? I'm guessing to some sort of music sensor. Check what is the input circuitry there? I can't find a service manual for this TT

 

[G401fan]

You can find the user manual of the AP 100C (basically the same model) in the vinyl engine site. You'll have to register first to get access to their manual 'Library' section. However, it does not provide an answer to your problem. Only a conductivity test, suggested by greenhorn, can help to locate the source.

 

[pathakajit]

I see two sets of wires going from the pcb. One of them to the RCA, but what about the other one? I'm guessing to some sort of music sensor. Check what is the input circuitry there? I can't find a service manual for this TT

I am not sure at the moment, greenhorn.
I do remember that the the other set of wires from the PCB run into the linkage and further split into two each.
Will pay closer attention to those when I open the TT for the continuity testing.. Been trying to find service manual for this TT but, no joy. Will try to match innards of this TT with the AP100c service manual as suggested by G401 fan..

 

[pathakajit]

You can find the user manual of the AP 100C (basically the same model) in the vinyl engine site. You'll have to register first to get access to their manual 'Library' section. However, it does not provide an answer to your problem. Only a conductivity test, suggested by greenhorn, can help to locate the source.

Thanks G401fan. I have download service manuals from vinyl engine in the past. I did see the other ap100c manual in the library. Will refer to it when my TT is open next for connectivity testing and compare the innards. Thanks.

 

[sachu888]

Very nice restoration. I think the problem with RCA cables of your TT. You can try swapping channels to confirmed. Do a continuity test as suggested by Green. The problem could Aldo be with your tonearm wires? OTOH you can contact some Pune members like Omishra, Sann etc for help.

Regards
Sachin

 

[kuruvilajacob]

If one channel of the cartridge is weak, you could experience weak signals from that channel

 

[pathakajit]

Very nice restoration. I think the problem with RCA cables of your TT. You can try swapping channels to confirmed. Do a continuity test as suggested by Green. The problem could Aldo be with your tonearm wires? OTOH you can contact some Pune members like Omishra, Sann etc for help.

Regards
Sachin

Thanks Sachin.
Problem follows to another amp. So, I'm definitely getting weaker output at the right RCA jack. Was unable to get the DMM today for the tests. Hopefully will be able to test tomorrow.

 

[pathakajit]

If one channel of the cartridge is weak, you could experience weak signals from that channel

Thanks kuruvilajacob.
Since the entire headshell assembly (HS+cart+stylus) seems to work well on other TTs, I do not suspect a weak cart at the moment.

 

[kuruvilajacob]

Can be due to problem with phono stage or amplifier>

 

[pathakajit]

Thanks Sachin and greenhorn!
The problem indeed turned out to be the RCA cables as revealed by the continuity tests.
The cables looked deceptively in good condition from the outside. Cut out the right cable and temporarily connected another cable for testing. Works fine now. Will get hold of a good set of S video cables (L/R/GND) as more permanent solution.

The TT has turned out really well. Its heavy and sounds nice. This TT arrived with an AT magnesium 10gm headshell and AT120E cart. Unfortunately, The stylus was broken. It will receive a new cart until I source the needle for AT120.

A short video of the TT in action-

AKAI AP103C fully automatic turntable: http://youtu.be/YlKpEWjTcb4

 

[greenhorn]

Will get hold of a good set of S video cables (L/R/GND) as more permanent solution.

The TT has turned out really well. Its heavy and sounds nice. This TT arrived with an AT magnesium 10gm headshell and AT120E cart. Unfortunately, The stylus was broken. It will receive a new cart until I source the needle for AT120.

A short video of the TT in action-

AKAI AP103C fully automatic turntable: http://youtu.be/YlKpEWjTcb4

congrats! Isn't it fun to find out and fix problems yourself

But why S video cables

The AT 120E seems to have a very expensive stylus. Planning on getting a genuine or generic replacement?


And the video seems to be privacy restricted - I'm unable to view it

 

[pathakajit]

congrats! Isn't it fun to find out and fix problems yourself

But why S video cables

The AT 120E seems to have a very expensive stylus. Planning on getting a genuine or generic replacement?


And the video seems to be privacy restricted - I'm unable to view it

Oops.. I mean to use a good set of video cables.. NOT S-video cable.

I would like to get the original replacement stylus for the cartridge - ATN120E/T. It is expensive and I will wait for it.

I have now made the video Public. Please check it out



Cheers!

 

[jls001]

Nice video.

The cartridge is fitted to innermost part of the headshell. Do check the manual for the correct mounting distance of the cartridge, so that you will get correct overhang (distance from the center of the spindle to the tip of the stylus). Also please do a null point adjustment. These two steps will refine your sound and you'll have lowered inner groove distortion.

 

[reubensm]

what a splendid looking TT, great work done on restoring it

For the issue you are facing, first check out the amplification just to ensure all's fine. Then zero down on the circuit between the cartridge and your amp. If that is fine and there is no open circuit, then its the cart. Your issue is a very simple one and if the cart and amp is ok, should take about 10-15 minutes to fix.

 

[pathakajit]

what a splendid looking TT, great work done on restoring it

For the issue you are facing, first check out the amplification just to ensure all's fine. Then zero down on the circuit between the cartridge and your amp. If that is fine and there is no open circuit, then its the cart. Your issue is a very simple one and if the cart and amp is ok, should take about 10-15 minutes to fix.

Thanks Reuben.
The TT is Now awaiting a new belt and so is in storage. Testing was done using a belt ordered for another TT. Belt is now Installed in the rightful owner

I believe the problem was the RCA cables and new cables will get soldered in soon.. Shall post updates once this is done and the TT comes into the living room setup