SOLVED: Harmon Kardon TU911: Not tuning

Thread Starter

richard3194

Joined Oct 18, 2011
162
Hi. I may need to study something on PLL, etc, but for now let me describe the fault. My TU-911 (FM only) tuner outputs noise. The display reads 87.5 Mhz and I cannot alter that. There is a button which has positions "seek/muting" & "manual". The tuning knob physically only turns a few degrees left or right. There are some memory buttons. Question: What can be inferred from the fact that the LCD is displaying a frequency, in this case 87.5 Mhz (apart from the fact that the LCD display is working)? I mean, is the PLL working? The tuner is described as "Digital Synthesized Quartz-Locked". I have the service manual. Could it be a typical fault? Thank you. Rich EDIT: The PLL synthesizer is TC9147BP.
 
Last edited:

abrsvc

Joined Jun 16, 2018
75
It sounds like the "tuning" chip is not working. The noise you are hearing is just a lack of signal. The fact that the up/down is not changing the freq suggests that either that "switch" is not working or that the IC has failed. I would check IC702 (TC9147) for proper voltages and the up/down pins for changes in position of the switch. Start there.
 

Dodgydave

Joined Jun 22, 2012
9,954
What happens when you press the memory buttons, are there any stations stored or does it still display the same 87.5??
 

Thread Starter

richard3194

Joined Oct 18, 2011
162
Hi. I've managed to fix it. Although the tuning is effected by turning a knob to the left or right, basically the tuning is a one pole two way switch. Well, that switch (SW6) was faulty, with no continuity either way. I shorted out that switch and got the Rx to tune up and down in steps, or got it to do a search. Problem solved. Rich
 

Thread Starter

richard3194

Joined Oct 18, 2011
162
Let me just mention that the faulty switch (SW6) is made by ALPS and is part number 745T. This might be hard to obtain. I guess there will be a substitute product. Not sure. Rich
 
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