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HK 730 FM Stereo Alignment

A Sound Mind

A Sound Mind

Reckless Tinkerer
I fully recapped this receiver (electrolytics), plus cleaned and inspected every inch of it. The power output transistors have new sil-pads and thermal compound. I replaced all the incandescent lamps. The idle current and bias adjustments were set to factory specs. It sounds great now, but a few issues remain; I'm unable to perform the stereo and FM alignments with the basic test equipment I have. Perhaps someone can suggest a workaround?
And the stereo indicator lamp won't come one. It's a new lamp and when tuned to a strong local stereo station and moving VR323 from end to end, the lamp won't even flicker. All the power supply voltage levels are near to spec and I confirmed for correct polarities on the new electrolytic caps. All the switches have been de-oxed.
Any ideas?
 
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When it comes to rf alignment there is no substitute for proper test equipment and you can mess up the alignment so the next person has a very difficult time of it.
Sound Technology ST-1000A stereo generator
Oscilloscope with 100MHz bandwidth
Keithley 2015 distortion analyzer
If you are doing this as a hobby, take it to a tech with rf skills. If you are charging customers to repair units, invest in the equipment.
 
It seems I've seen something about IC301 (HA1156W) failing and causing this issue before. The service manual has voltages listed, and block diagram from lamp to IC in order to check operation.

Good luck,

Mark K.
 
I've got one with the same issue, PO tried to put in a new STEREO bulb and blew the bulb fuse.
I still get FM but not stereo and can get the stereo bulb to come on if I fake a HA1156 ground.

Are all HA1156 chips the same? I've got a couple of them on parts boards.
 
"moving VR323 from end to end". VR323 or did you mean VR301? Is the audio output in stereo or mono? i.e. is it just the stereo indicator light that is not working or is the stereo decode non-functional?
 
I performed more testing and found the following which may/may not have a bearing on the stereo indicator issue:

B+ at the EQ amp is +21.6V. Spec calls for +14.87V. (B- reads -14.03V)

The HA1156W (IC301) drives the indicator lamp. Pin voltages read: (Actual, Factory)
1: 12.12, 11.93
2: 2.09, 3.04
3: 2.61, 5.08
4: 9.28, 8.49
5: 9.14, 8.43
6: 12.78, 12.66 (this pin does not change state when tuning)
7: 0.2, 0
9: 2.33, .08
9: 2.33, 2.27
10: 1.54, 1.53
11: 2.33, 2.15
12: 2.33, 2.32
13: 2.33, 2.31
14: 3.1, 3.17

Should I replace this IC?
 
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Ylli said:
"moving VR323 from end to end". VR323 or did you mean VR301? Is the audio output in stereo or mono? i.e. is it just the stereo indicator light that is not working or is the stereo decode non-functional?
Click to expand...
I meant VR353. Sorry. The service manual says it affects the stereo indicator .
 
A Sound Mind said:
I meant VR353. Sorry. The service manual says it affects the stereo indicator .
Click to expand...
VR353 basically sets the threshold where the receiver sees enough signal to enable stereo decoding. The pot that you want to adjust 'end-to-end' is R301.
 
A Sound Mind said:
I fully recapped this receiver (electrolytics), plus cleaned and inspected every inch of it. The power output transistors have new sil-pads and thermal compound. I replaced all the incandescent lamps. The idle current and bias adjustments were set to factory specs. It sounds great now, but a few issues remain; I'm unable to perform the stereo and FM alignments with the basic test equipment I have. Perhaps someone can suggest a workaround?
And the stereo indicator lamp won't come one. It's a new lamp and when tuned to a strong local stereo station and moving VR323 from end to end, the lamp won't even flicker. All the power supply voltage levels are near to spec and I confirmed for correct polarities on the new electrolytic caps. All the switches have been de-oxed.
Any ideas?
Click to expand...
There is no inexpensive way to get into alignment. If you can find a Panasonic, Leader, Kikosui or Kenwood synthesized AM/FM/FM Stereo generator at a price you can live with they're probably the best bet. Most of the older generators will need some kind of refurb by now.

BTW, I'm curious why you used thermal compound with Sil-Pads.
 
Ray Gianelli said:
There is no inexpensive way to get into alignment. If you can find a Panasonic, Leader, Kikosui or Kenwood synthesized AM/FM/FM Stereo generator at a price you can live with they're probably the best bet. Most of the older generators will need some kind of refurb by now.

BTW, I'm curious why you used thermal compound with Sil-Pads.
Click to expand...

I don't do enough of these to justify investing in expensive FM stereo alignment equipment which also require training.
I mainly work on vintage and antique radios, phonographs, tape decks, CD players and such and my shop is well equipped for these.
However, I've successfully restored 50 or more stereo receivers of various makes over the past 35 years without a single complaint, so I must be doing something right.
I use high grade thermally conductive paste along with Sil-Pads for a little extra cooling. It couldn't hurt!
 
Thermal compound is designed to fill in small/microscopic imperfections in the mating surfaces. The Sil-pads do that on there own. Adding thermal compound just adds another layer of thermal resistance to the heat path.
 
Ylli said:
VR353 basically sets the threshold where the receiver sees enough signal to enable stereo decoding. The pot that you want to adjust 'end-to-end' is R301.
Click to expand...
Turning R301 had no effect when tuned to a strong stereo broadcast.. Would the IC be the main suspect? If not, what signals should I be looking for?
 
Yes, the IC would be the most likely suspect. Look at the voltage on pin 6 with a voltmeter. If should be about +13 with no signal being received, and near zero with a strong stereo station tuned in. If you have a scope, you can look for a 19 KHz signal on TP301. With no signal input you would normally adjust VR301 for 19.00KHz at that point. You could also trace the composite audio from the input (pin 2) to the output of the chips pre-amp (pin 3). Beyond that, replacing the chip might be the quickest fix.
 
Ylli said:
Yes, the IC would be the most likely suspect. Look at the voltage on pin 6 with a voltmeter. If should be about +13 with no signal being received, and near zero with a strong stereo station tuned in. If you have a scope, you can look for a 19 KHz signal on TP301. With no signal input you would normally adjust VR301 for 19.00KHz at that point. You could also trace the composite audio from the input (pin 2) to the output of the chips pre-amp (pin 3). Beyond that, replacing the chip might be the quickest fix.
Click to expand...
I replaced IC301, ($15!) but nothing changed. Pin 6 reads around 12.6 volts and it's state never changes when tuning. 19KHz is present at TP(LP)301. Composite audio is present at pins 2, 3 and 11 on the IC. I retested the lamp and traced its connections, which are all good. What can I try next? Perhaps I should pull and test all transistors in that circuit?
 
Lift one leg of R309 (connected to IC301 pin 8). See if you can get the stereo light to come on then.
 
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