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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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29th Nov 2012, 10:36 am | #1 |
Hexode
Join Date: Aug 2011
Location: Luton, Bedfordshire, UK.
Posts: 469
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Harman/Kardon 330c receiver distortion
Hi guys,
My HK 330c receiver (in the family since 1979 or 1978) is exhibiting a dodgy right channel. This seems to be across the board, all inputs and radio. The volume coming out of the right channel is lower than the left, in order to achieve any sort of balance I need to turn the balance knob to about 2 o'clock but even then it's clear that the right channel is distorted and has less bass than the left. I have switched the speakers over to be sure it's not a speaker or crossover issue. In addition does anyone know where to get lamps for the tuner display? One has been dead for about 20 years Any ideas what I should be testing for? I am reasonably handy and have such things as a multimeter and oscilloscope. Thanks for any help. I am considering buying something similar on eBay but would rather repair this one if possible. |
29th Nov 2012, 11:09 am | #2 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
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Re: Harman/Kardon 330c receiver distortion
That should be easy with a scope.
A sine wave from a signal generator would help even more. Just put the scope probe on the base and collector of each transistor until you find one that does not compare with the good channel. Starting at the input as output faults usually blow fuses. The only output fault that can cause this symptom is if it has capacitor coupled speakers and one it open circuit. Measure the DC voltages on all three pins. Then just check both ends of the coupling caps either side of it. Measure the 3 or 4 resistors around it. If a capacitor is leaky it will make the base of the following stage high voltage with distortion and if it is open circuit low bass. I would say less than ten components to check here. The transistor itself is less likely to be faulty but a quick diode test range check will do no harm. |
29th Nov 2012, 6:22 pm | #3 |
Hexode
Join Date: Aug 2011
Location: Luton, Bedfordshire, UK.
Posts: 469
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Re: Harman/Kardon 330c receiver distortion
Thanks for the advice. I have a signal generator and should have the time to look at it over Christmas.
I even have the circuit diagram somewhere. |
10th Jan 2013, 11:18 am | #4 |
Hexode
Join Date: Aug 2011
Location: Luton, Bedfordshire, UK.
Posts: 469
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Re: Harman/Kardon 330c receiver distortion
Well I had time to take a can opener to my beloved HK330c.
I replaced all the scale lamps in the end, and it's made a huge difference. Cleaned everything I could including all the switches, the output transistors had a huge amount of dust. I know it hasn't been opened in over 30 years. Using the 'scope I couldn't find anything wrong so after cleaning the knobs I put everything back together and it seems that the cleaning was all that was necessary. The sound is now great from both channels and the "mono" switch works for the first time in many years. The other switches are much less noisy though the tape monitor switch is still a bit dodgy. Anyway I've uploaded a photo to show how it looks now...and one taken of me listening via headphones in 1979. Don't I look happy! Last edited by Gulliver; 10th Jan 2013 at 11:24 am. |
10th Jan 2013, 11:47 am | #5 |
Heptode
Join Date: Apr 2008
Location: Eastbourne, East Sussex, UK.
Posts: 671
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Re: Harman/Kardon 330c receiver distortion
What a lovely bit of kit, well worth repairing.
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10th Jan 2013, 12:03 pm | #6 |
Hexode
Join Date: Aug 2011
Location: Luton, Bedfordshire, UK.
Posts: 469
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Re: Harman/Kardon 330c receiver distortion
Sounds very sweet too. I think it just needed a little TLC, it has had a lot of use down the years but interspersed on three occasions with a couple of years inactivity due to circumstances.
For the last 12 years it has been *the* main audio source in our home, including the amp for L and R in a surround system and it's hooked up to the desktop PC. So be it music, computer or movies, the HK330c is used. |