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Old 5th October 2017, 01:51 AM   #1
arsmith60 is offline arsmith60  United States
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Default TU-8600 build- the mystery of no left channel

Being a huge Elekit fan- the TU-8600 is one of a number of kits I have assembled over the last few years. All of them went together perfectly due in part to the great assembly manuals- and taking time to make sure all components are being assembled in the correct locations.

After completing the TU-8600 kit- I moved the TU-8200 out and connected the newly completed amp. I turned the CD transport on....and flipped the TU-8600 power switch on (with volume turned all the way down....). All tubes were glowing, and as I slowly turned the volume up I noticed I only had output on the right channel. The left channel was absolutely silent.....Checking speaker and CD connections did not change anything. Nor did swapping tubes...

I turned the amp off, and pulled the covers off of the power supply and PC board. I then ran a voltage check on all the taps that are called out in the Assembly Manual. All voltages were in spec. The interesting thing is that on a couple of the tap pads I got an audible "chhhhhhk" on both the right and left channel when the probe hit the pad. This would later be an important hint..

I ended up checking and re-flowing the solder on all the left channel components on the PC board. I also checked all the parts for polarity, and the correct values in their correct spots...Feeling confident I had most likely fixed the issue- I installed the PC board in the chassis and reassembled the amp. Hooking it back up- nothing had changed. Still no left channel.

I emailed Victor for any ideas he may have- and I ended up swapping the OPTs (with no change). Victor commented it could be a solder joint issue...

After taking the amp apart several more times....checking more components and solder joints...and re-assembling....I was still without a left channel. Thinking about the voltage check and noises I would hear on both channels....I figured that the problem had to be after the amplification circuitry....so I moved my attention to ALPS pot....could it be bad?

Removing the ALPS pot and PCB from the amp- I tested the pot I noticed that the left channel lead was being grounded out somehow....Under a microscope I found a tiny solder bridge that went across the left channel pad to one of the unused pads just behind the front lead solder points......I cleaned up the area between the pads....re-installed the ALPs pot and PC board.....re-assembled the amp....connected everything.....and I now have beautiful music!

Thank you Victor for including the voltage check chart in the assembly manual. That helped a ton in finding the problem. I am extremely pleased with the TU-8600. This amp really makes my Cornscalas come alive.
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Old 5th October 2017, 05:51 AM   #2
gavinb is offline gavinb  South Africa
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During my 8340VK build, I noticed when inserting the PCB RCA connectors the force of insertion can easily bend/fold the centre pin pcb tab backwards as it happened with me on one.

I was able to de-solder and bend it back.

If you still had a problem I would have suggested the possibility.

Last edited by gavinb; 5th October 2017 at 06:14 AM.
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Old 5th October 2017, 11:06 AM   #3
arsmith60 is offline arsmith60  United States
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Great feedback gavinb. Those were my thoughts exactly when I was re-checking my solder joints and continuity testing. The left channel RCA jack and left channel speaker solder joints were my first suspects....

-What power tubes are you running in your TU-8340?
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Old 6th October 2017, 11:38 AM   #4
gavinb is offline gavinb  South Africa
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Genalex Gold Lion KT77 with Mullard E180CC phase splitter and Brimar 6060 on input. 45W/UL mode.

Volume control is ELMA-A47-SMD-STEREO 50K stepped attenuator. (47 step)

Last edited by gavinb; 6th October 2017 at 11:44 AM.
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