Tuner on Harman Kardon HK430 silent

[mqtthiqs]

Hello,
I am looking for some technical help from a good soul. I posted this thread a few months ago but no visitor seemed to have enough knowledge of tuner electronics; therefore this new attempt.

FM reception on my HK 430 receiver stopped working after a couple months of perfectly fine reception. It cut intermittently 1/2 weeks before turning completely silent (a few seconds/minutes of silence). Now FM, stereo or not, is dead silent; the rest of the receiver works perfectly, including AM.

The tuning meter moves correctly when I turn the tuner jog dial. The FM muting button is off, and the muting sensibility pot on the back has no effect. The selector switch is clean and working.

I checked voltages with the help of the service manual (p. 10 of this PDF); some look not exactly in range but I cannot tell if it's within acceptable error. Here are my (quite random) measurements:

Q205 w/ Mute OFF: E 0.0V C 7.4V B -0.34V [Expected: 0.0V 7.97V 0.07V]
Q205 w/ Mute ON: E 0.0V C 0.12V B 0.62V [Expected: 0.0V 0.08V 0.63V]
Q206 w/ Mute OFF: E 5.90V C 5.25V B 7.32V [Expected: 6.06V 6.05V 7.97V]
Q206 w/ Mute ON: E 5.90V C 5.87V B 5.20V [Expected: 6.05V 6.05V 5.36V]
+B3: 12.4V [Expected: 12.5V]
-B2: -30.4 [Expected: -28.5V]
+B4: 24.2 [Expected: 25.4V]

Q301 B 1.54V, E 1.07V, C 4.04V [Expected: 1.75 1.11 4.03]
IC301: ok except Pin 8: 2.62V [should be 0.12V]

Q201: ok
Q202: drain at 6.43 [should be 4.89]
Q203:B 6.23 [should be 4.89], E 5.58 [should be 4.19]
Q204: B 6.22 E 5.59 C 8.96 [should be 4.89 4.19 6.25]
Q303, Q304: ok

If someone would be kind enough to interpret the schematics & these measurement, I would be extremely grateful!
Thank you in advance,
-m

 

[Punker X]

Kinda points to IC301... No audio at all, in any condition, but the meters are moving, tells me MPX, Audio, Muting. Voltages look good, except at the chip. Have you played around with VR301 and 302, 301 sets VCO to 19Khz, and will light the stereo lamp if adjusted properly. 302 sets stereo threashold or muting. At low level with either switch to mono or mute. Given the symtoms without the voltages I would susepect IC301 or Q302

 

[mqtthiqs]

Thank you for your help! Do you confirm that I can tweak VR301 and 302 just by ear, without equipment to tune it afterwards? What should I look for when doing so?

 

[Punker X]

To align it properly you would need the test equipment, but you can rough adjust it. Tune the a strong station and turn 301 so the stereo lamp lights. I'd mark the pots before you start so you can always take them back to their original position. The threshold adjustment you can all the way counterclockwise should disable and allow it to work in stereo no mater what. I'd adjust there first. I could be wrong about the counterclockwise, it could be clockwise. I'm really not that intimate with this tuner. Try counterclockwise first, then adjust 301 to try and get the stereo lamp. If it doesn't work, then try clockwise and readjust 301. If you get a stereo lamp then return 302 to it's original position then the stereo lamp should stay lit. Hopefully you get signal out.

Given your symptoms, I'm doubtful the adjustments will do anything.

 

[mqtthiqs]

Will try and report back, thanks again!

 

[mqtthiqs]

Hi there! Finally got time to test and switch a few components... still no dice.
Adjusting VR301 had no effect: the stereo lamp never lit up.

I went on and replaced IC301 with an equivalent BA1310F. It fixed everything (radio out, stereo lamp) for a few minutes, and then went off again. I then replaced Q302, it made no difference; still no sound and no stereo lamp. Maybe the old Q302 fried the new IC301?
Now I get the same reading on IC301 as before (all pins ok except Pin 8 at 2.68 instead of 0.12). Reading on Q302: E 0, B 0.05, C 2.68.

Next up, I was thinking of replacing C307 (and C303, 305 and 306 while I'm at it) but I need to go buy some; what do you think? Any advice on what I should get?

 

[Punker X]

Wondering if the stereo lamp has been replaced with one that draws too much current. Looks like it is driven directly off from the chip. Would explain it working shortly then, not. Spent a bit of time looking for the listing for PL6 in the manual, not much luck, but guessing its a 30ma bulb. If replaced with a 50ma or higher could burn out the chip.

 

[mqtthiqs]

Thanks for the idea; I'll look into this, despite that it doesn't look like it was ever opened before me...

 

[39cross]

If you don't see any lamp issues per PunkerX, here is a suggestion. (also, after scouring the manual top to bottom I found the reference to lamp P6, see p18, its 6.3v, 40mA).

I see VR302/Q302 are connected to something labelled A3, maybe a jumper wire? This connects to R232. In the vicinity is an 0.47uf tantalum cap.
This is not an elegant approach, but it if was mine, I'd replace the tantalum and electrolytic caps and recheck the voltages. This step may not correct the issue, but it shouldn't hurt (unless somehow you put in a cap backwards). Also check the solder joints on the board.

 

[mqtthiqs]

Thank you all very much for your help!
Incredibly, I turned the radio on 2 days ago and it worked perfectly (2 days after having changed the chip and transistor mentioned above). I still need to test it over longer time, and will probably recap for safety, but for now it seems like the problem... solved itself?

 

[mqtthiqs]

Hello, sorry to revive this old thread. Contrarily to my message above the problem is still there: when I turn it on after some weeks unplugged, the tuner works correctly for a few seconds and then suddenly the Stereo lamp turns off and only silence. The tuning VU-meter still responds correctly when I turn the dial

I changed:
- IC301
- Q302
- the tantalum cap mentioned above
- the few electro capacitors close to the IC on the diagram.

I re-checked voltages after putting the new caps, and it did not change anything (still as per my post above).
Any idea before I reluctantly put this thing for sale at a ridiculous price? I have access to an oscilloscope.