Checking the FM signal Strength on a SX-1010

zebulon1

Working on my own stuff. Finally
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I received an sx-1010 which had trouble tuning in stations (Among many other things). It was in sad shape when I received it but after cleaning/lubing the VC shaft and cleaning the fins it showed new signs of life.
The signal meter never really recovered, never showing any real strong stations when tuning in the local frequencies. The best I could get was about half scale on stations I normally get near full scale on other tuners. This still holds true.
I have a Sound Technology 1000A and after connecting it up I can adjust the RF Level on the ST-1000 to -85db and hit 5 on the 1010's signal strength scale. The SM never discusses the adjustment. I see VR3 will adjust the meter.
What I'm asking, is there a standard for this adjustment? Or does this tuner have other issues? My ST and 1010 are set up and tuned to 98MHz, modulated at 400Hz,
Note: Beginning to get familiar with this RF thing.
 
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Most of the Pioneers I have worked on have the same procedure for the Signal level meter adjustment.
When I did my SX1010, I used I think maybe the SX1250 as a reference.
Pioneer like you to totally saturate the tuner with 100db (RF ref) and the meter just under 5.
The meters aren't that accurate so it seems Pioneer think close enough is good enough. When they say set the meter to 4.7 or 4.8, well, thats just an approximation because there is no marking for 4.8, it goes 4 then 5.....

On the 1250 they want 100db to show 4.7 on the meter.
100db is some scale the Japanese manufacturers came up with. Its an odd scale!!
But 100db is 50mV. That is a LOT is signal to put into a tuner antenna input.

I set my 1010 like that, and funnily enough, it read the same (or very close) as my G9000 Sansui, and most other tuners I have worked on recently with the same scale.

The other thing I have noticed lately with these ageing tuners is weak transistors in the IF stage, the tuner will seemingly work okay, you get more back cleaning the Air Cap, but still doesn't seem right, I had this with a Sansui TU9500 last week, replaced the IF stage transistors, different tuner!!

What scale is your ST1000A using? dbm/db/mV? What impedance is the output of the RF Gen?
The other thing to consider if it you are using a Balun, to make sure you account for the loss through the conversion....My HP8657A is 50Ω, so I have a balun to use the 300Ω antenna inputs as this is what almost everything references in manuals.
If it is 75Ω makes sense to use the 75Ω antenna input an then your levels will be correct.

How much modulation are you using?

RF is a little bit using your instincts and following your nose....anyway I am sure we can get the meter near enough...
 
I still have to warm up some on this equipment but I set the pilot level to 400hz. Not sure what voltage I have at the antenna terminals, the DMM is not connected. I’ll do that next. Just looking for a course idea of the issue. The FM is wonky but pulls in stations, somewhat on the weak side.
The Balun is one I built, 50 to 300 ohms and seems to work well.
All the frequency settings, 88, 98, and 108 fall in spot on between the receiver and ST1000. Separation is good and the stereo light stays on all the way down to about 8dB. The RF Level can be read in dB or uV. Tomorrow I’ll check another receiver comparing the two.
 
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I use the 75 ohm coax input, bare wire terminals. The 1010 uses same RF FE as the 1250.
On JoJo's 1250 one of the trim caps was way off. They are stiff, I used the Bourn's plastic trim pot tool, blade out, it did not de-tune when I touched it.
RF alignment 101 from Motorola portable radio production line :)
Learn to use the RF generator with no modulation to quiet the tuner and to fine tune the caps at ~108MHz. Muting off, listen to the noise on the speakers and watch the signal using a analog ACV meter which has good bandwidth to 100KHz, monitor at the tape out L or R, fm selected of course :) You can tune to a strong signal, then reduce the level to ~1uV or where all you get is noise then increase the Rf level until it starts to quiet, use that level ~3dB of quieting to adjust the trim caps for best quieting or lowest ACV. The trim caps are touchy.
You could also go down the dial to 88MHz and fiddle with the coils but they tend to not need adjusting. They say they are interactive so you have to try and tune for best quieting on both ends.
I set the 1250 meter to full scale, based on the strongest signal I could receive using the antenna mounted on the tower. You can also use 100mV

See where this gets you.
 
Thats a good tip Rick about the no modulation, I am going to try that on the next one!! Thats an an excellent idea.

I always to both ends, coils and trimmer caps, because they do indeed interact....


I am not sure why Pioneer specify 50mV and then say set to 4.8 on the signal level meter, where is 4.8?? Would have been much better to give a level which related to 5 on the scale!!
 
I still have to warm up some on this equipment but I set the pilot level to 400hz. Not sure what voltage I have at the antenna terminals, the DMM is not connected. I’ll do that next. Just looking for a course idea of the issue. The FM is wonky but pulls in stations abet on the weak side.
The Balun is one I built, 50 to 300 ohms and seems to work well.
All the frequency settings, 88, 98, and 108 fall in spot on between the receiver and ST1000. Separation is good and the stereo light stays on all the way down to about 8dB. The RF Level can be read in dB or uV. Tomorrow I’ll check another receiver comparing the two.
You know, I think those Signal level meters are just a rough guide to actual RF level, and what Rick says makes a lot of sense.
I've done so many alignments now I just kind of know where it should be. A lot of the time I am working with a 500µV level doing various parts of the alignment, and that tends to show a level of 3-3 1/4 -ish on those meters that read 1-5.....
If you feed that level of RF carrier into the tuner, allow for the loss through the Balun, if its reading less than 3 then something is wrong, be it alignment or component related...
I found the 1010 tuner was very sensitive and responded well to alignment, quite easy to do.
Sounds like you have a gut feeling something isn't quite right, I'd go with your gut feeling!! Its usually right!!
 
When tuning the receiver it seems very sensitive and it’s easy to pass the stations once tuned they are stable. It’s just not that easy to tune.
When reading some of the hints and tips in the ST-1000A’s SM discusses using the “Duel Sweep” pattern to get a symmetrical response? A small amount distortion actually makes the customer happy. This seems my issue with the 1010.
 
When tuning the receiver it seems very sensitive and it’s easy to pass the stations once tuned they are stable. It’s just not that easy to tune.
When reading some of the hints and tips in the ST-1000A’s SM discusses using the “Duel Sweep” pattern to get a symmetrical response? A small amount distortion actually makes the customer happy. This seems my issue with the 1010.
Sometimes I go for a visual for a discriminator, but a lot of the time I just use the Distortion analyser, its easier I find, or even sometimes I use both just to double check, but it always ends up with the THD measurement being the deciding factor in the last tweak of the discriminator.

It does sound like an alignment issue, whats it like tuning in FM MONO?

The other one to do on the Pioneer tuners is the lissajous pattern for the 76khz oscillator in the MPX, I find they are often a bit off, and that can cause the stereo reception to be a bit off, a bit distorted...
Sometimes requires the replacement of the osc trimmer....they go bad just like any other old trimmer.
They outline the procedure for the lissajous in the manual, it uses the scope in X/Y mode, 19khz pilot into the horizontal input and then the output of the 76khz osc into the vertical (usually on a TP near the MPX chip), and you adjust for a 4:1 ratio. Basically if the pattern is rotating, you adjust the trimmer to make it stationary. There's usually a sample display in the manual...
Its pretty accurate for setting that osc....

I've got my old TEK465 set up specifically for X/Y use.....
 
I mucked with the 1010 tuner board and now something is weird.
I accidentally messed with the AGC and Output control trimmers. How can I get them back?
I believe I have them set to the original spot but would like to get them set correctly.
The stereo seems to center to the right of the center meter both on the 1000A and local stations. It may of been correct before I tinkered with it.

I'm beginning to get the hang of this by self teaching but it is getting frustrating. I'm missing some basic knowledge.
 
I mucked with the 1010 tuner board and now something is weird.
I accidentally messed with the AGC and Output control trimmers. How can I get them back?
I believe I have them set to the original spot but would like to get them set correctly.
The stereo seems to center to the right of the center meter both on the 1000A and local stations. It may of been correct before I tinkered with it.

I'm beginning to get the hang of this by self teaching but it is getting frustrating. I'm missing some basic knowledge.

Hmmm not sure what you mean, what trimmers were these. Can you point them out on the schematic/circuit board layout so I can have an idea of what you have adjusted?

What you are describing sounds like either the TUNE meter is out of adjustment, or the discriminator is off.
In the 1010 procedure, they have you use a Distortion analyser for the discriminator.
For centering the meter they want you to have the FM SG connected, but the output level turned down. They are wanting you to make the tuner "deaf" for this adjustment, but I like to simply short the antenna to ground, I find that works better.
So you could try that (use the 75Ω connection, and short that out).
Once you have done this, if the needle is off, adjust the lower core of that big silver coil in the middle of the board, and adjust until its centred. If you're not sure if you're in the lower core, you can access it from the bottom of the unit, they have a convenient hole in the circuit board to access it.

Then, they want you to adjust the upper core to get minimum distortion.

This is my favourite method for doing the discriminator, its been getting me the most consistent and best results.

Maybe Rick will chime in too, he is a bit of an RF guru!! Knows a lot more than I do!! But we can get this tuner back....Its a little bit holding your tongue the right way and only doing certain adjustments on a full moon etc etc....
 
AGC and Output control trimmers
What part numbers?

Step 10.1.5 is used to center the meter. I put the DMM across pins 7 and 10 of HA1137 and adjust for a DC null. You can put your DMM across the center tuning meter as well.
 
What part numbers?

Step 10.1.5 is used to center the meter. I put the DMM across pins 7 and 10 of HA1137 and adjust for a DC null. You can put your DMM across the center tuning meter as well.
Agreed, that is also a good one too, not enough resolution on the tune meter itself, but can use it for a quick and dirty ball park adjustment...

I am slowly compiling my own method for alignment, taking ideas which work well and devising a good hybrid method...
 
Thanks for the help.
The two trimmers I messed with are VR4 and VR5. For the AM. I looked at the procedure for the settings and it seems straight forward reading about it. I’m sure it’s a hole lot different when actually doing it. :whip:
 
sometimes it is better to learn to measure some of the specs before you adjust anything.
For example they have the spec for quieting sensitivity. I explained how to measure mono quieting sensitivity, what RF level do you need for 20dB of quieting?
No RF, set your ACVmeter for 0 dB on the scale, by adjusting the sensitivity vernier. you are not concerned about absolute level, since it is a relative measurement.
Increase the unmodulated RF level until the ACVmeter drops 3dB,10dB, 20dB, etc, how many uV is needed in each case?
 
Thanks for the help.
The two trimmers I messed with are VR4 and VR5. For the AM. I looked at the procedure for the settings and it seems straight forward reading about it. I’m sure it’s a hole lot different when actually doing it. :whip:

Yeah I was wondering if it was in the AM section you might have adjusted which is why I asked.

Adjusting the Discriminator is like doing DC offset. I guess Pioneer don't want us probing with a DMM or similar in there and loading the circuit to check DC offset, so using a distortion meter is a good way of doing it when you have no access to a sweep gen with markers, you simply cannot sweep a Discriminator without markers to do a visual alignment, you're flying blind, so they go for a MIN THD reading which is where the null point is for no offset.
Its also a good way of doing it without loading the circuit too as the Dist meter is on the Tape REC output.

Rick's method will work if you don't have a Dist analyser. But definitely do it at the Tune Meter drive as he suggested.

It is that easy. Make sure you do the meter calibration before setting the Discriminator.
 
Okay, A recap of the sx-1010's tuner mishap:
The two trimmers I messed with are VR4 and VR5 for the AM, AGC and Output control. I think I get that back without any help. Cross your fingers.
The FM circuit is unmolested but is not tuning correctly.
When tuning a FM station the center meter is slightly off to the right when the stereo light illuminates and the strength meter is at full swing strong.
This is with all the local FM stations and with the ST 1000A tuned to 98MHz and in stereo.
I'm going to complete the discriminator adjustment as Rick and kev advised.
 
Okay, A recap of the sx-1010's tuner mishap:
The two trimmers I messed with are VR4 and VR5 for the AM, AGC and Output control. I think I get that back without any help. Cross your fingers.
The FM circuit is unmolested but is not tuning correctly.
When tuning a FM station the center meter is slightly off to the right when the stereo light illuminates and the strength meter is at full swing strong.
This is with all the local FM stations and with the ST 1000A tuned to 98MHz and in stereo.
I'm going to complete the discriminator adjustment as Rick and kev advised.
I forgot to ask, was it like this when it came in to you?

It will definitely will come right when you align the Discriminator.
 
Yes, the receiver was a mess. Leaking Filters, two early repairs by a service center using original pioneer components. Not well done.
I noticed the FM tuner when doing the evaluation.
The tuners when not working, I can fix. In most cases they fire back up, run and need no adjustment. This I knew would need some tweaking.
Tuner board is original and was left alone. No work done on it.
 
Made the centering adjustment and re-set VR4 and 5 for the AM. All is working. I spent some time ciphering through the manuals for the the ST 1700 trying to figure out the connections/operation of the two. Using the distortion analyzer in conjunction with the ST 1000A would make a nice set-up. I think it's possible. Sound Technology does tend to think of everything.
 
Sounds like this 1010 has had a hard life!!

Yeah the AGC is the Auto Gain Compensation, pretty straight forward.

There should be a diagram in the Pioneer manual for the basic setup to do the alignment..

I reckon you'll get it sorted, man of your talent should find it straight forward.
 
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