Pioneer SX-1980 APC Adjustment

[Jon1982]

Wonder if one of you pioneer buffs could help me?

I'm trying to adjust the APC circuit in accordance with the service manual. However the manual talks about an "L2" pot which I cannot see anywhere and I am unable to get the waveform to change as described... the quartz lock does work, sort of.. so I'm guessing either the setup procedure is written wrong or I'm doing something daft. Thanks in advance

 

[rcs16]

I am reading SM page p36, APC adj procedure 10.3 step 4, it says to adjust L2, it does not saying anything about a pot, so I assume they are referring to L2 coil on AWX-124.
Look at page 63 for its location, use a nylon tuning tool.
I have never done this procedure so I am not sure if it is correct or not.

 

[markthefixer]

L2 is a square silver/chrome IF transformer looking thing, right next to VR1.

Since the procedure calls for a pin 12 connection AND pin 12 (not far from "TC" ) is only accessible with the cover OFF, I assume you have the cover off.
Still, use the cover as your guide.
The hole marked "L" on the cover right next to the VR1 hole is the one you want.

With the cover off you will have birdies galore.... AND be VERY careful putting the cover back on, there are some hanging components (cap? IIRC) that if mis positioned, will short to the reinstalled cover.

I always breathe easier once I have the APC aligned and back together.

 

[Jon1982]

Guys, thanks for all the replies so far. I didn't seem able to adjust the waveform as per step 4 of 10.3. I looked around the board for suspect components and despite my novice skills I found a weak electrolytic, decided to change all three, and now it seems I can adjust the waveform.

All steps of 10.3 I can do ok, EXCEPT step 6. The voltage is stubbornly ~20V AC between terminals 8 & 7 and VR1 has little bearing on it.

Given that the other adjustments check in Okay, and given that VR1 does affect the quartz lock operation (if set wrong it seems to make the lock 'chitter' in and out) I am starting to suspect that there is an error in the adjustment procedure. Can anyone advise?

PS thanks for the warning about the underside components!

 

[Dihan Angelo]

Hi All

I have a query!! what does the APC function do in a 1980? i tried to read up about this in the manual but still none the viser!

appreciate if anyone can explain what and why and how the APC circuitry work

thanks

 

[markthefixer]

FM stations broadcast on tightly controlled frequencies, and are quite predictable as to frequency spacing, xxx,x00,000.00 megahertz ... like 102.5 megahertz = 102,500,000 Hz

APC uses a crystal (quartz crystal) controlled oscillator to define a target frequency to be tuned, in discrete jumps - snapping to a frequency, skipping over the intervening bandwidth. In 100,000 hz steps.(100khz)


Listener may want to tune to 93.7, which is 093,700,000 mhz and by manual knob twisting achieves 093,705,247, then APC backs it down to 093,700,000.
If / when things start to drift, APC corrects it. Thus "quartz lock" - quartz for the crystal, lock for the action.
if the crystal drifts slightly (a couple of hertz) - the receiver will follow and slightly mis-tune.
Broadcast stations use frequency standards far more tightly controlled than a mere quartz oscillator.

 

[pcindunil]

FM stations broadcast on tightly controlled frequencies, and are quite predictable as to frequency spacing, xxx,x00,000.00 megahertz ... like 102.5 megahertz = 102,500,000 Hz

APC uses a crystal (quartz crystal) controlled oscillator to define a target frequency to be tuned, in discrete jumps - snapping to a frequency, skipping over the intervening bandwidth. In 100,000 hz steps.(100khz)


Listener may want to tune to 93.7, which is 093,700,000 mhz and by manual knob twisting achieves 093,705,247, then APC backs it down to 093,700,000.
If / when things start to drift, APC corrects it. Thus "quartz lock" - quartz for the crystal, lock for the action.
if the crystal drifts slightly (a couple of hertz) - the receiver will follow and slightly mis-tune.
Broadcast stations use frequency standards far more tightly controlled than a mere quartz oscillator.

Hi..Mark , Do you have any experience of repairing and alignment of APC of Sx-1980..Thanks.

 

[zebulon1]

L2 is a square silver/chrome IF transformer looking thing, right next to VR1.
Since the procedure calls for a pin 12 connection AND pin 12 (not far from "TC" ) is only accessible with the cover OFF, I assume you have the cover off.
Still, use the cover as your guide.
The hole marked "L" on the cover right next to the VR1 hole is the one you want.
With the cover off you will have birdies galore.... AND be VERY careful putting the cover back on, there are some hanging components (cap? IIRC) that if mis positioned, will short to the reinstalled cover.
I always breathe easier once I have the APC aligned and back together.

This was a timely post. I have a 1980 here for a right amp repair. We decided to go with the (863-MJL21193G , 863-MJL21194G) outputs, which was nice because I needed a few of the good 2SB406/2SD746's for another project.

Anyway, as I was repairing the 1980, it was falling apart. Dropping channels and a quirky APC. The APC settings were close (as far as I could determine, first time messing with this circuit) so I figured it was something more sinister. After removing the VC cover. I noticed the cover solder tabs to the board were already desoldered. Someone else was tinkering around in there. Cleaning the VC was needed but the real fix was resoldering the cover tabs back to the VC board. That explains why it was working when I was twisting and touching the VC module, thinking it was bad bonding.

Mark,
Could you explain the APC board adjustment procedure?
I tried it with no RF generator, only using the local stations but decided to look for something more likely than settings.

 

[rcs16]

The adj procedure tells you to
check the reference 100kHz, but it fails to tell you to what accuracy it should be set for. Using a 10:1 scope probe and a frequency counter, I set it as close as I could get it.

 

[pcindunil]

This was a timely post. I have a 1980 here for a right amp repair. We decided to go with the (863-MJL21193G , 863-MJL21194G) outputs, which was nice because I needed a few of the good 2SB406/2SD746's for another project.

Anyway, as I was repairing the 1980, it was falling apart. Dropping channels and a quirky APC. The APC settings were close (as far as I could determine, first time messing with this circuit) so I figured it was something more sinister. After removing the VC cover. I noticed the cover solder tabs to the board were already desoldered. Someone else was tinkering around in there. Cleaning the VC was needed but the real fix was resoldering the cover tabs back to the VC board. That explains why it was working when I was twisting and touching the VC module, thinking it was bad bonding.

Mark,
Could you explain the APC board adjustment procedure?
I tried it with no RF generator, only using the local stations but decided to look for something more likely than settings.

Yes it will be a great help both of us.

 

[pcindunil]

The adj procedure tells you to
check the reference 100kHz, but it fails to tell you to what accuracy it should be set for. Using a 10:1 scope probe and a frequency counter, I set it as close as I could get it.

100kHz is ok .But wave foam @ IC M5S003P pin not Shure. Anyone know about this.

 

[kevzep]

100kHz is ok .But wave foam @ IC M5S003P pin not Shure. Anyone know about this.

Generally a digital scope cannot produce a lot of the waveforms in the land of RF. Use an analogue scope.
Like for example the lissajous pattern and so forth, you won't see that on a digital scope.

The other thing worth checking is the 5VDC supply which I believe runs the 100khz Oscillator, the 1980 I did had an issue with that supply and it was causing issues with the OSC...