HA1156W Divider and VCO wave forms

[caltechi]

Gentlemen,
I'm at the end of restoring a Pioneer SX-636. On the final test of all the functions i noticed that although I can pull FM stations in, they will not receive in stereo. (Same issue prior to the restore) I've done a cursory alignment of the RF and IF stages which were not far off at all however FM reception is challenging even with a basic cheapo balanced 300 ohm antenna connected. I've read all the posts I could find on similar issues and followed the advice.

So here's the rub. Everything in the circuit is working as it should including all voltage measurements on the ICs and such. So i'm pretty sure it is a poor reception issue or the HA1156W itself as I can inject a 19kHz directly to pin 2 of the IC and the stereo indicator line on pin 6 will not go low. What I haven't seen is what the wave forms from the divider and VCO should look like so I'll post them for you all. Please let me know if i'm seeing what I should. Thanks in advance for your responses!

 

[chazix]

Please let me know if i'm seeing what I should.

Those waveforms look plausible to me. They don't reveal anything about whether the PLL is "in lock", but I believe that at least the VCO and divider are working

HA1156W pin 8 is used as a stereo mode inhibitor (in addition to its LPF role). Did the DC voltage measurement there come out as expected (looks like 2.3V, if I'm seeing the schematic scan clearly)? If that was OK, then I don't think the decoder is being externally inhibited.

There's some chance that the problem is with external passives, like maybe the small electrolytic caps. It might be worth checking the Pioneer forum to see if any are known to be troublesome, or you could replace them speculatively.

HTH,

chazix

 

[caltechi]

Hi Chazix,

Thanks for the quick response and confirmation on the waveforms. I also noted that about pin 8 on the data sheet, and it is sitting at the proper voltage. All the tiny blue Sanyo elctrolytics have been replaced with film caps and the styrol cap that sets up the VCO checks good, as do the mica and the disk caps used in the surrounding circuitry. I suppose I could verify the resistor values. Even though they rarely fail, I guess anything's possible.

I did notice thst both the VCO and divider frequency seem to be a bit unstable when tuned to a strong signal and even more so when not. From what I understand, the two should be rock solid in either condition. That's why I'm suspecting the IC itself. I did also clean the VR that adjusts the VCO.

 

[chazix]

rock solid in either condition

In my experience, it's normal for the VCO frequency to jitter around unless the input is either a suitably strong stereo composite signal, or else no signal at all (e.g., if the receiver is tuned to a strong but un-modulated carrier).

If you're getting noise-free monophonic reception, I agree with your suspicion that the HA1156 is bad.

 

[caltechi]

Again, thanks for your reply. I'll see if I can source an IC and follow up with the result. I'll also take your suggestion and repost this in the Pioneer form just I case there might be something else I missed. The circuit itself is pretty straight forward for this unit and does not deviate very far from the test circuit in the data sheet with the exception of a BJT switch to ground on pin 14 that's activated by the mode selector and another one on pin 8 that's activated by the audio mute line. Both of which have been test and are working as expected.

Tim

 

[39cross]

I noticed you wrote "FM reception is challenging even with a basic cheapo balanced 300 ohm antenna connected."
Is this true for your location, or just this unit? Is the signal strong enough to kick into stereo? Are you using the OTA stations, or do you have a stereo signal generator?

 

[caltechi]

Hi,

It's my location. OTA stations are weak however I can receive at least one station at 3 S-units which should be sufficient. I have an AV receiver with a digital tuner I could try and make sure I'm not experiencing a weak signal induced problem. I do not have a stereo generator but I do have the capability to FM modulate a 19kHz signal on my sig-gen. I've also tried to inject a 19kHz signal directly into pin 2 of the H1156W IC and can see it lock in when monitoring pin 10 but the stereo lamp driver on pin 6 remains high.

 

[39cross]

Seems like that station ought to be strong enough. I am currently working on an SX-737, same MPX IC. I can do measurements if that would help.
The SX-737 SM has an MPX adjustment, VR2, I think this is the pilot. The SM mentions setting up a scope for a Lissajous pattern, however I think you can use a frequency counter at the test point and check for/adjust for 19khz. You've probably already done this.
Maybe Dr. Audio will come along and confirm Dr. Chazix , time for an HA1156 replacement.

 

[caltechi]

Nope. You're right on. My SM says the same thing except the adjustment is VR1. My scope has a freq counter built in to the math functions so I aligned it that way. I felt the whole lissajous pattern thing was a bit un necessary if one has a frequency counter. But yes if your circuit is working and you could take a look at the wave forms on pins 10 and 14 and see if they look like the ones I posted that would be helpful. Also if you could verify that injecting a 19kHz tone into pin 2 will activate the stereo beacon that would be awesome too. I see no reason why it wouldn't work but I don't have a working unit so I can't verify it.

 

[39cross]

Yes, I can give that a shot. I can't generate a pure 19khz tone AFAIK, but I can check the two waveforms with mono and stereo signals.

 

[caltechi]

That would be great!
Thanks!

 

[rcs16]

The 19KHz pilot signal is not modulated, it is a sinus reference, that is to have about 7.5KHz(10%) of deviation on the composite signal. It is used to re-generate the 38KHz switching signal to recover the side bands from the AM modulated L-R carrier.
I see that you have the ~76KHz free running VCO, it has to be adj to be within the PLL capture range. The VCO is divided down to 19/38KHz, it is to be phase locked to the incoming 19KHz reference. The PLL has a certain lock/capture range so the VCO is set nominally at 76KHz to be within the PLL capture range (See the spec)
I think that the stereo lamp indicator just requires the PLL to lock onto the pilot of sufficient amplitude, in the ?mV range(need to look at the spec) as minimum to detect and sink the lamp I.
With a scope, you should see the 38KHz switch freq on pins 4 and 5. pins 4,5 are pulled up with R's to pin 1. Pin 10 is the VCO monitor point, it usually has a 100K R in series with the TP.
See what you can measure out of the VCO adjustment range and see if you can get it close to 76KHz.
Check to see if the lamp is okay as the ST lamp driver is open collector, thus it needs a pull up in order to sink I. In some cases they put a large R(~>=50K) across the lamp to verify the pin is going low even if the lamp is open.

Good Luck

 

[caltechi]

Rcs,

Thank you for the detailed description of the MPX function. The VCO frequency is in the capture range as you described. I have verified that the stereo lamp is good. If I understand correctly, injecting an undulated 19kHz signal at an amplitude of 12 ~ 20mV (per the data sheet) at pin 2 of the IC should trigger a lock condition and light the stereo beacon by going low on pin 6.

 

[rcs16]

Still good to put a 10K across the ST lamp and make sure pin 6 is at Vcc when no pilot present. Also, grounding pin 6 will verify your lamp. I think you know whats going on
I think injecting a pure 19KHz(+/-3%) sine(>=20mV) into pin 2 is a valid test condition. pin 2 is at a internal DC bias, you measured it against the sch, so the signal has to be AC coupled of coarse.
Since we have a internal ckt to follow, we can follow the signal a bit monitoring the pins. the 19KHz(composite) goes into pin 2, is buffered and comes out on pin 3, through the cap (50n) into pin 11.
from pin 11 it branches into the phase comparators. The phase comparators are pwm sq waves(your scope shot shows this) that when LPF applied creates the PLL correction voltages(pin 9 & 13), the voltage to run the pilot detector ( internal comparator) to the lamp driver.
A lot of talk for a cheap part, but it is PITA if you order/replace the part to find out it is one of the passives that are the cause (been there). but you changed most of the passives, do above checks to test my analysis (BS detector) & for the fun of it but I think it is the chip. So socket and a new chip.
I see there are a few suppliers on ebay,
https://www.ebay.com/itm/1PCS-HA1156W-DIP14-IC/322918594646?hash=item4b2f72b856:g:S4YAAOSwnCFaI057
I would try this supplier, I have never used them, so we know it may be risky and may take a while to get it but the price is right if you are tight for $, if you need asap use US supplier. I know littlediode takes at least a month for me at least.

FYI, I was advised and bought on ebay (<$200) an old HP/Agilent 8904A(opt 001) it makes a great piece of test gear as a FM composite source and general purpose sig gen.

Good luck
Rick

 

[chazix]

Before resorting to ebay to source the chip, my own preference would be to try a more-or-less-well-known supplier of vintage parts. A fave of mine is Consolidated (ceitron.com). I don't know if they've got HA1156 in stock, but it's likely. You'll need to either think of some other stuff you need (cleaning chemicals, perhaps), or else pay a handling fee on top of already pretty high shipping fees, but it is my belief that Steve does not knowingly sell bogus parts.

 

[rcs16]

I know in another Pioneer thread, someone purchased a chip from Consolidated (ceitron.com) and it worked fine.
I see they have one and the price is low, best to go there I agree
http://www.ceitron.com/semi/ceihitachi.html

 

[39cross]

I checked pins 10 and 14, on my DSO I see the same thing on pin 10, 19khz square wave. On pin 14 I am not seeing anything on the scope. The frequency counter on my DMM reported 67kHz.

 

[caltechi]

Thanks 39cross! I appreciate you taking the time to check that. It's odd that you can't see a waveform from pin 14 on your scope though, and the frequency should be 76kHz. Did you flip the numbers? rcx and chazix, thanks for the heads up on the possible HA1156W suppliers.

After all the trouble shooting of external passive components and neighboring circuit functions and finding them to be working as expected, I have attempted to validate the HA1156W operation using the following 2 methods with no success:
1) FM Modulated a 90mHz carrier with a 19kHz tone at 7.5kHz deviation with my sig gen and fed it to the receiver which was tuned to the same frequency. I am able to see the demodulated 19kHz sine wave present at pin 2 of the HA1156W but pin 6 (stereo beacon driver) is still sitting at VCC. The lamp is good. I verified it out of circuit.
2) injected a 19kHz sinus tone @ 20mV ac coupled directly on pin 2 of the HA1156. No beacon.

At this point I'm fairly confident that the device is defective. I will procure one from the vendor recommended by rcx and chazix, install a proper IC socket and retest for correct operation. I will report back with my findings. In the meantime I've got a couple of other repair/resto projects to start on. A Fender Cyber Twin hybrid Guitar amp and an Ampeg VT-22 tube amp guitar amp. The fun never stops!

Tim

 

[Punker X]

I would also recommend Consolidated for the part also this crosses to a NTE801, which is available and should work.

 

[39cross]

It's odd that you can't see a waveform from pin 14 on your scope though, and the frequency should be 76kHz. Did you flip the numbers? r

I got out my other scope and was able to reproduce the sawtooth waveform on pin 14, but it is 65kHz. I tried again with the DSO and must have had missed something, because this time I got the same sawtooth waveform result -- and it also reported 65kHz. I don't know why it isn't 76kHz like yours, is that good or bad or indifferent. Just to see what would happen, I adjusted VR2 and could get it to read a max of about 72kHz, I then readjusted it back to the original measurement.

Anyway, good luck with your replacement!