OK, understood. Will be able to take a look at the alignment in the next week. Do I need to build the "Detector Probe Block" shown in the SM to go between the tuner RCA out jacks and the oscilloscope? They are also showing a 100 pF capacitor between the signal generator and TP 1. I will have to look around to see if I have that or can easily get one.
You need to forget about the procedure in the SM, that will only work with a Genescope.
I use hybrid methods, Pioneer have really good procedures, as they were obviously realistic about what test gear most shops would have, so I have combined their methods into most of the tuners I work on...Sansui expected every shop to go out and buy one of these annoying Genescope things, PIA!!
You can use the visual method for the IF, but in order to do that its imperative to have visual markers for the peak of the 10.7mhz IF frequency and usually 200khz each side of 10.7mhz. I think the SG165 has a 10.7mhz sweep with markers, but you have to use that function with respect to the instructions in the SG165 manual otherwise you wont see them and then its all guess work.
I use a wide-band noise source and my Spectrum analyser to do IF visually because the SG165 doesn't work with some tuners and its fiddly as hell to set up, although I have used it a few times, its just really time consuming, I need to be able to do it quicker as I am on the clock. Plus on the Spectrum analyser I can read the amount of level through the IF in dbm so its easy to peak it out.
If you are wanting to do visual, yes you need a proper detector probe, that is not specific to Sansui, it changes the signal into a variable signal which can be displayed on a scope, and yes to inject the sweep into the IF stage you need a DC blocking capacitor, ceramic is best.
Its always best to have the scope connected to the REC OUT so you can observe the Audio signal, and this is where I also have the Distortion analyser connected and the VTVM, this way you can peak out the various stages and confirm its correct with minimum THD+N.
The Detector out is used for visually aligning the Discriminator, but thats a load of hoopla to make that work, so again, Peaking and Min THD+N, you can use a DMM to set the offset to 0mVDC as well, but the Distortion analyser is also a powerful tool here....
This is what I find on the tuners I do.
>IF is always pretty close UNLESS someone has had the great golden tweaker in there, so I always check the IF for that, back in the day, only qualified techs would have been in there, but these days in the world of DIY who knows whats been done to it.
>The Discriminator is almost always slightly out, this causes bad stereo reception and distortion.
> Most VCO's need a tickle up
> Discrete Multiplex circuits are always off and need a good going through, its quite time consuming to do these and get a good result.
> PLL Multiplex circuits are always very stable and not much needs to be done there unless they have 19khz and 38khz traps, these can always do with a tickle, not much usually.
> Stereo separation always needs a tweak...
Once you have done a few and get the feel for it, then it becomes pretty straight forward.
