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-   -   Harman Kardon 690i Funky Tuner Board (http://www.diyaudio.com/forums/analogue-source/205992-harman-kardon-690i-funky-tuner-board.html)

A Sound Mind 5th February 2012 12:09 AM

Harman Kardon 690i Funky Tuner Board
 
This receiver works great............except for the tuner.
The tuner display and controls work, but have no effect on the output.
I get FM hiss and AM static, but no signals on either band.
There is an exception: When I place my finger on pin 1 of IC201 (HA11225), I'm hearing 2 blended FM stations and they're from over 1000 miles away! The led power meter also activates when I do this. I've checked all around the board for correct voltage levels and they're good. Grounds are good too. Connectors are properly oriented. A complete visual inspection of the PC board under magnification turned up nothing special. I have the service manual and schematics, but the manual doesn't offer much help in troubleshooting and the schematic is rather tough to follow. There are several test points on the schematic, but I can't find any reference to them in the documentation. (please see the attached docs)

I'd really appreciate any help from anyone out there who's had some experience with HK tuner boards. Or maybe one of you might have an old board that needs a good home?

raindog 5th February 2012 09:49 AM

The HA11225 is the IF amplifier/ detector for the FM section and since it seems to be working your problem might be in the front-end section ( most likely miss-aligned rf circuits ) .

A Sound Mind 10th February 2012 01:23 AM

Don't know where to go with this advice. What equipment and procedures do I need to track down the cause of this problem?

raindog 10th February 2012 04:00 PM

Can you post the schematics please ( it would be easier to explain the procedure ).

A Sound Mind 10th February 2012 06:36 PM

The service manual is too large for this forum.
Here's a site where it's available for a free download.

Thanks for your help!

raindog 10th February 2012 09:10 PM

I think you forgot to paste the link for the site :)

raindog 10th February 2012 09:48 PM

1 Attachment(s)
I found the service manual ( google helped :) ). First you should check TP11 for voltage ( it should be between 1.5 and 2.3 volts and it should vary with the movement of the tuning knob - it's the control voltage for the variable capacitance diodes ). If that's ok you should try to adjust the oscillator coil ( first "tune" the receiver so the scale indicates a frequency of a strong local station ) and see if by adjusting the coil ( if it's an "air" coil - with no core - just press gently the turns of wire closer together or further apart until you hear ( possibly very faintly ) the station it's supposed to be tuned to. If it doesn't work some components - most likely the oscillator transistor - are defective. If it works adjust the rf amp coils and lastly the if coil for maximum sound.
All of the above is a somewhat crude approach but it doesn't require any specialized equipment . For a more technical and accurate method you would need a signal generator and an oscilloscope ( capable of handling signals in the 89-108 Mhz range ) and check all the components and adjust the coils.

A Sound Mind 11th February 2012 12:00 AM

Oops. Glad you found the schematic. The receiver doesn't pick up anything at all. Neither AM or FM. Even with a good antenna tuned to a local station. I can scroll up and down with the digital tuner, but it just picks up hissing, so I know a part of the tuner is still working. I'll follow your directions and see what I can find. I'm not very experience with RF circuits, but I do have a signal generator and a 200mhz scope, so perhaps you could guide me through the rest of troubleshooting.

raindog 11th February 2012 07:51 AM

Ok, let me know what you find and we'll take it from there.

raindog 11th February 2012 07:55 AM

P.S. using the oscilloscope check TP7 to see if there is signal there and if the frequency varies with the movement of the tunning knob.


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