TV and VCR tuner modules

How to use surplus modules.

I am sure that at some part in your life as radio ham or electronics enthusiast you must have looked inside the inards of a recently discarded VCR or idiot box and wondered to what good use you could put the tuner module. The module has generally wide UHF coverage and nearly complete coverage of the  LOW  and HIGH VHF bands and completely eletronically tuneable.  Specifications are nearly impossible to come by. The really old modules could be reverse engineered, but anything more recent than the last 15 years has been extremely well made with micro miniature components and reverse engineering them is out of the question.  I have noticed that the pinouts seen to follow some loose conventions and the signal levels also appear to follow a loose convention.

I have come across some construction articles using these devices , usually for the construction of UHF spectrum analysers, making good use of the fact that they are varactor tuned and can be scanned very rapidly, but again the articles refer to very specific tuner models that have only transient availability.

These two circuits came from a service manual for a long gone vcr I once had and will provide enough information as to application and voltage levels that will enable you to use a tuner module for whatever.  The only things that really come to mind are spectrum analyser front ends or homemade tuneable wideband scanners.  The circuits show only how the module is driven, nothing about the module internals is available. It seems that there are only one or two companies that make these modules and they are used by nearly all tv set and vcr makers. I think Phillips used to make them as well. In  fact they probably made them all!  

I have discovered that Phillips™ seem to have spun off their division that made these devices. They are now known as NXP  and can be found here www.nxp.com.  Good luck in finding a product spec for these older devices. This site lets you search by part number only, and these modules allmost never have a part number on them!

The tuning range of these devices seems to encompass about 400 to 850 Mhz,  130-230 Mhz and 45 to 110 Mhz in 3 seperate electronically selectable bands.  The tuning voltage requires up to 30V for varactor  reverse bias. I cant really tell what the AFT voltage range is but I suspect holding it constant at some voltage between 0 and 12 is required.  The power supply looks like it wants to be 12 V.  The IF output has usually only one tuned resonator on the output and I guess its centered on maybe 42 Mhz, but the Q is kept low to keep the required IF bandwidth high. The IF output is low impedance to permit small runs of coaxial cable to be driven.

My guess of the signal lines is as follows.  Most tuner modules have these pin markings appearing either on the module itself or on the pcb to which its mounted. The nmenonics seem to be mostly consistent but mileage will vary.

It would appear that to select a band the appropriate select signal is high (+12v) , the others should be permitted to float low.  My guess for the sense of AGC that it is a signal between 0 and 12V+ and forward agc will be used for best linearity and low noise figure, so that means as the AGC voltage goes up, gain should go down. It would appear that on modern tuner modules PIN diodes are used to provide the variable gain function.  However some data sheets suggest the opposite is the case. I guess you just have to experiment.

The IF centred frequency is an educated guess, forty something Mhz has been the traditional standard.  The SAW filter that it feeds should be the guide but its usually impossible to get a specification on these.