Well, he's still around, but he refused the work.
Said there aren't parts for it anymore, and he "sold enough of them that I'm gonna pass". Couldn't get a recommendation from him on who would. Crap.
Well, he's still around, but he refused the work.
Said there aren't parts for it anymore, and he "sold enough of them that I'm gonna pass". Couldn't get a recommendation from him on who would. Crap.
kevzep
Its all about the Music
Whats wrong with these people and this "unserviceable" nonsense, you just want someone to Align the tuner....Wonder if the vintage stereo repair shop originally farmed it out to him in the first place, hence the title of this thread.
So, I've been recapping while I've been waiting for the various "poor-man's alignment" tools to arrive, and when I finally got around to the FM IF and MPX boards things improved slightly (there are now about 4 stations I can get intermittent "solid" FM STEREO indicator lights on), but I still have the intermittent FM STEREO flickering during AUX, PHONO, AM, etc. which it clearly should not be. I checked the SELECTOR switch circuitry and it looks clean, so I started looking in the schematic for any potential sources of noise... that's what the flickering resembles most... it's not steady, repetitive, or responsive to me probing the antenna inputs, etc... It stabilizes slightly when I probe a couple of test points on the MPX board with a voltmeter, but is still never solid.
Replaced the caps on the ripple filter board, things looked even better. Started tracing signals from the ripple filter board to see where they led... a small board, F1120, which is not in the service manual but is in the schematic. A couple of electrolytics, replace... look, a transistor! Can't read what it says on the side, but check the schematic... uh oh...
Yep. My old friend 2SC458 directly in the signal path from the IF out to the MPX in. If ever there were a (somewhat) predictable source of noise that could be it.
I'll be replacing that now, then aligning with dr*audio's suggestions. The oscilloscope came in and I'm playing with it now. It has a 1kHz generator as a calibration signal, but it's square wave, not sinusoidal, so alas I'll have to use something else to modulate into the FM.
So I'll be playing with the oscope until I get some KSC1845Fs on hand. Probably best to keep some around anyway if I'm going to keep restoring these old delights.
Replaced the caps on the ripple filter board, things looked even better. Started tracing signals from the ripple filter board to see where they led... a small board, F1120, which is not in the service manual but is in the schematic. A couple of electrolytics, replace... look, a transistor! Can't read what it says on the side, but check the schematic... uh oh...
Yep. My old friend 2SC458 directly in the signal path from the IF out to the MPX in. If ever there were a (somewhat) predictable source of noise that could be it.
I'll be replacing that now, then aligning with dr*audio's suggestions. The oscilloscope came in and I'm playing with it now. It has a 1kHz generator as a calibration signal, but it's square wave, not sinusoidal, so alas I'll have to use something else to modulate into the FM.
So I'll be playing with the oscope until I get some KSC1845Fs on hand. Probably best to keep some around anyway if I'm going to keep restoring these old delights.
kevzep
Its all about the Music
Well, you need a carrier wave in the FM band which can frequency modulate and accept external modulation as well so you can use a multiplex generator, the multiplex generator does the MPX signal with the 19khz pilot tone.
You can't do any work in the MPX circuit without a multiplex signal.
You can just FM modulate with a tone 400hz but that will only be good fo setting up IF and discriminator.
You might be able to get a Sencore SG165 for cheap, they do everything, not horrendously accurate in carrier wave though, they have IF sweep with markers and Multiplex....so everything you need.
They all have a shaft on the frequency dial that breaks, apart from that they are a pretty solid unit.
Oscope is essential so you can look at your audio through the tuner and peak out the stages. VTVM like a RCA VoltOhmyst is also really handy with that high impedance and large analogue meter.
To align the discriminator which could be part of the problem, I like to use the distortion analyser, I find its the most accurate, the next best way is sweeping with markers.
With this fault on your unit, the flickering of the FM Stereo light in another function selection is probably the transistor which switches the light on and off. They use a signal from the MPX once its receiving a pilot it then turns on a transistor which then turns on the light when the transistor fully saturates.
So the power is present on the lamp all the time, but is switched at the transistor.
If the transistor is a bit leaky/faulty, that light with flicker and sometimes even turn on.
The other thing I am finding now with these older tuners, and the TU9500 I was working on the other day was a classic example, is its not uncommon to find a faulty RF transistor in there, just after the front end in the IF stage, I've had that a few times lately...
Let us know how you get on...
You can't do any work in the MPX circuit without a multiplex signal.
You can just FM modulate with a tone 400hz but that will only be good fo setting up IF and discriminator.
You might be able to get a Sencore SG165 for cheap, they do everything, not horrendously accurate in carrier wave though, they have IF sweep with markers and Multiplex....so everything you need.
They all have a shaft on the frequency dial that breaks, apart from that they are a pretty solid unit.
Oscope is essential so you can look at your audio through the tuner and peak out the stages. VTVM like a RCA VoltOhmyst is also really handy with that high impedance and large analogue meter.
To align the discriminator which could be part of the problem, I like to use the distortion analyser, I find its the most accurate, the next best way is sweeping with markers.
With this fault on your unit, the flickering of the FM Stereo light in another function selection is probably the transistor which switches the light on and off. They use a signal from the MPX once its receiving a pilot it then turns on a transistor which then turns on the light when the transistor fully saturates.
So the power is present on the lamp all the time, but is switched at the transistor.
If the transistor is a bit leaky/faulty, that light with flicker and sometimes even turn on.
The other thing I am finding now with these older tuners, and the TU9500 I was working on the other day was a classic example, is its not uncommon to find a faulty RF transistor in there, just after the front end in the IF stage, I've had that a few times lately...
Let us know how you get on...
Ah. Makes sense. So that would implicate TR408 being flaky, or I suppose most anything prior to that, really.
Hey, while you're reading... why KSC1845 rather than, say, KSC1815 as a replacement for 2SC458?
So, in my oscope playing, I've been trying to puzzle put what's going on with my AM section. It's dead to the world (translation: not even static coming out). I'm getting the impression that's a sign of problems in the IF end, so maybe that's a topic for another time.
I did probe the oscillator circuitry next to the tuner gang just to see what it looked like... pretty sine waves with amplitude around 1V, but they're coming in from 960 kHz to 1.9MHz or so depending on where I have the tuner gang dialed into...
I think the oscillator is supposed to be at 455 kHz, so I'm assuming this wave is supposed to be the LO + the tuned frequency? That would almost fit, though it's a bit off.
Any idea what I'm seeing? I'm trying to understand the physics of what I'm doing as well as the engineering, and I guess I expected the oscillator to be closer to 450 kHz and not get into the higher frequencies until mixed with the amplified antenna signal. Or is the simple act of probing changing the signal itself?
I did scope the transistor activating the FM STEREO lamp as you suggested, and there's definitely something funny going on there. It's supposed to drop to 0V when "active", pulling the bottom of the lamp voltage down and making it light from the 8V high end voltage on the other side... I get that.
I'm seeing TR408 (the transistor in question) dance around between like 1.2V and 0V, so something flaky is there. When I probe the base of that transistor, it's jumping back and forth from about 20mV to 0V... is this because the prior transistors in the path (TR407 and beyond) are flaky, or because I am getting enough base-to-emittor current draw when TR408 flips out that it manifests as a voltage drop at the base?
I did probe the oscillator circuitry next to the tuner gang just to see what it looked like... pretty sine waves with amplitude around 1V, but they're coming in from 960 kHz to 1.9MHz or so depending on where I have the tuner gang dialed into...
I think the oscillator is supposed to be at 455 kHz, so I'm assuming this wave is supposed to be the LO + the tuned frequency? That would almost fit, though it's a bit off.
Any idea what I'm seeing? I'm trying to understand the physics of what I'm doing as well as the engineering, and I guess I expected the oscillator to be closer to 450 kHz and not get into the higher frequencies until mixed with the amplified antenna signal. Or is the simple act of probing changing the signal itself?
I did scope the transistor activating the FM STEREO lamp as you suggested, and there's definitely something funny going on there. It's supposed to drop to 0V when "active", pulling the bottom of the lamp voltage down and making it light from the 8V high end voltage on the other side... I get that.
I'm seeing TR408 (the transistor in question) dance around between like 1.2V and 0V, so something flaky is there. When I probe the base of that transistor, it's jumping back and forth from about 20mV to 0V... is this because the prior transistors in the path (TR407 and beyond) are flaky, or because I am getting enough base-to-emittor current draw when TR408 flips out that it manifests as a voltage drop at the base?
Not quite, the Local Oscillator (LO) runs at the signal frequency + the IF frequency.
So if the incoming signal frequency is 1000Khz then the LO should run at 1455Khz.
Thanks. I apparently misunderstood that from "the literature".
It's close, so at least I know the oscillator is running (mostly) correctly. The output test point after the antenna signal amplifier is what I'll look at next. I'm not picking up an AC signal there at most spots on the dial, but I'll keep looking.
It's close, so at least I know the oscillator is running (mostly) correctly. The output test point after the antenna signal amplifier is what I'll look at next. I'm not picking up an AC signal there at most spots on the dial, but I'll keep looking.
kevzep
Its all about the Music
You need to run your RF oscillator with say a 400hz or 1khz audio tone riding on it.
We don't actually look at the RF frequencies, we look at the audio tone.
The LO is at 455khz, it gets mixed into the RF carrier at the mixer. TR302.
But don't worry about that, get you RF Osc going at say 1000khz and tune in.
Then you can start looking for the audio after the first IF stage if its not appearing at the output.
AM receivers are actually really simple, look at the AM alignment and follow along with the instructions.
Not quite, the Local Oscillator (LO) runs at the signal frequency + the IF frequency.
So if the incoming signal frequency is 1000Khz then the LO should run at 1455Khz.
1455khz after the mixer, the LO is 455khz and it is measurable at the LO.
Sure, but i'm not trying to align it right now, just do basic troubleshooting and learning, i.e. is the oscillator even running-- I'm definitely getting something that looks a lot like LO + carrier at 3D... hmmm...
I'm still not sure about the Service Manual, btw... while I see TC303 as the trim cap for alignment at higher carrier frequencies in the SM and in the Alignment instructions, all I see on the actual board is the coil (T302) and a wire leading directly to the tuner gang (VC302)... no trim cap evident anywhere. The conventions of the schematic imply that TC302 is not on the circuit board, but I'm not seeing where it could be. It's puzzling.
I'm still not sure about the Service Manual, btw... while I see TC303 as the trim cap for alignment at higher carrier frequencies in the SM and in the Alignment instructions, all I see on the actual board is the coil (T302) and a wire leading directly to the tuner gang (VC302)... no trim cap evident anywhere. The conventions of the schematic imply that TC302 is not on the circuit board, but I'm not seeing where it could be. It's puzzling.
Yeah, the coils are obvious. The trim caps less so. I'm headed home to the workshop now so I'll look again. I googled after this and someone posted a Sansui 2000 photo of the trim caps actually physically on the chassis of the gang tuner, and it occurs to me that maybe I missed it this morning when looking for it.
smurfer77
Super Member
Just wanted to chime in and say this is a cracking thread. sorry, I don't have much more to add than to say it the whole affair is entertaining and educational, so thanks to OP for their perseverance and thoughtful approach and all those helping along with their expert advice.
AK is a great place!
AK is a great place!
kevzep
Its all about the Music
Yes this is what the situation normally is, often the LO trimmer cap is not on the tuning gang. But the rest are, then you need to not get the FM trimmers mixed up with the AM trimmers.
AM is the fine bread slicers, and the FM is the Coarse bread slicers, the FM slicer does your toast bread!!
ghazzer
Senior Member
For those of us who are enjoying this thread, but just barely able to follow along, can someone suggest basic reading material that would help us to a better understanding of how tuners "do their thing"? I'm talking 'KISS', as I can only absorb so much each month.
I know enough to know to keep my fingers off the bread slicers, thanks to Dr*Audio's tuner cleaner thread.
Thanks - - -
I know enough to know to keep my fingers off the bread slicers, thanks to Dr*Audio's tuner cleaner thread.
Thanks - - -
Right now on my phone I have the following tabs open to refer to:
Sansui 5000X Service Manual
A guy building his own AM radio from scratch
Tuner tweaks just short of a full alignment, which I'm not following but which I find okay for reference material
Details of FM stereo modulation scheme
There are probably books I can buy that would give me the right information, and certainly we covered the basics of some of this stuff 25 years ago in school, when I was much smarter but also much dumber, but really, the interactive effect of kevzep and dr*audio and maxhifi and Hyperion here, not to mention the guys on the tuner thread, have been priceless and inspirational.
Also, I picked up a used copy of this book years ago and it sat on my shelf a quarter-finished until recently. Highly recommended for its use of layman's terms, from a simpler time.
Sansui 5000X Service Manual
A guy building his own AM radio from scratch
Tuner tweaks just short of a full alignment, which I'm not following but which I find okay for reference material
Details of FM stereo modulation scheme
There are probably books I can buy that would give me the right information, and certainly we covered the basics of some of this stuff 25 years ago in school, when I was much smarter but also much dumber, but really, the interactive effect of kevzep and dr*audio and maxhifi and Hyperion here, not to mention the guys on the tuner thread, have been priceless and inspirational.
Also, I picked up a used copy of this book years ago and it sat on my shelf a quarter-finished until recently. Highly recommended for its use of layman's terms, from a simpler time.
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