Harman Kardon T55C

[calebtbecker]

Hello everyone, I hope all is well.

I've recently acquired a Harman Kardon T55C turntable. How exciting. Its in good cosmetic condition, but it seems to have some electrical issues that I am having trouble sorting out. I've read multiple instances on this forum of other owners of this model experiencing issues with the turntable motor not starting or starting but not staying on for more than a moment. This, too, is the case in my example. I read that a fix to this is to locate the capacitor C118 and replace it. I found this capacitor and saw that it was not holding a charge, and that it had discharged its electrolyte many years ago and ate away all of the solder and copper on the PCB. Disgusting thing. Since replacing the capacitor, it holds a charge but it did not resolve the issue of the motor starting. Before replacing the capacitor the motor would start but not stay moving, and after replacement, it does not start at all when the tone arm switch is switched on. I'm hoping somebody could point me in a more educated direction or offer some in put before I take my next approach. Oh and also, the quartz lock light does not turn on either when its button is engaged.
Much appreciated, I thank you for your time.

 

[heyraz]

Check your work. Clean between the copper traces, make sure there are no shorts.
Make sure the polarity is correct for the capacitor you replaced.

I'm surprised only one capacitor failed. It sounds like you have three issues...motor, end of record control and quartz lock.

Post pictures of both sides of the boards.

 

[Aerobat]

I don't think these tables hold up very well over time. I have one sitting in the original box, despite going through it and replacing the cheap electrolytics, pulling the platter bearing and cleaning/re-oiling, oiling the motor, and adding the right new belt, it still has poor speed control and the quartz lock doesn't work. As a bonus, the super-light arm wants a high-compliance cartridge. Oh and if you step anywhere near it, the arm jumps out of the groove.

 

[calebtbecker]

Here is the patch job that had to be done since the copper pads were all eaten away. I have been checking the voltages across some of the other capacitors at the 2 different speeds and a few come up with 0V. No other capacitors have seemed to leak but that does not exclude them from being inoperable. It would seem the power regulation circuits are working, as the LED for the tone arm position sensor light up. I checked the motor, it seems there is approx. 11V are going to it on both 44 and 33rpm, and the speed. The two terminals that accept the PWM signal for the 2 speeds seem to be getting voltage but at this moment, I don't have an oscilloscope to check if they're actually doing what they're suppose to. I speculate the motor may be at fault, so I will test that next. The leaking capacitor came out like a rotten tooth, with just a few wiggles.

 

[calebtbecker]

I checked voltages on the terminals of the motor. The tonearm switch is working, the power to the motor is turned on/off with the opening and closing of the switch. The quartz lock seems to affect the magnitude of the voltage of the speed control signal, for the white terminal, it is a noticeable difference but for the brown it is only 0.001v off 0.002v on. I only have a standard voltmeter at home, so I cannot check the pulse modulation, which I think these lines are responsible for. I suspect the motor is what is at fault. Though that doesn't explain why it was seemingly working at the start of all this before the replacement of c118. Will keep going. How frustrating. I will try removing the wire and see if I cant get it working with an external power source.

 

[heyraz]

You should be able to download the T55 and T60 service manuals. They have a schematic that may help you.

 

[heyraz]

A friend's T65C behaved as your T55C... It would spin briefly and immediately stop. These two capacitors were the problem.

Notice the vents on the top 2200uf are distended with slight traces of electrolyte.
(That's not electrolyte between the caps and the board... it's glue).

These 2 caps were replaced and the turntable runs again.

 

[Ilikevinyl]

View attachment 3535936
A friend's T65C behaved as your T55C... It would spin briefly and immediately stop. These two capacitors were the problem.

Notice the vents on the top 2200uf are distended with slight traces of electrolyte.
(That's not electrolyte between the caps and the board... it's glue).

These 2 caps were replaced and the turntable runs again.

Thanks for sharing! I'll have to check my T55C and see if those caps are like that too. Hope that will be the problem only!

 

[calebtbecker]

Interesting. None of the capacitors in mine are of that size or are laid down like those. But I will double check that the ones on that PCB are operational. Thank you for the feedback.