Not uncommon is now for sale (at a price 2-3 times lower than new) in the bazaars of the former in the use of VCRs, imported, particularly from Germany. The main problem faced by the unsophisticated consumer, is that these video recorders are not able to reproduce on our TV soundtrack (meaning when connected via a high-frequency input on the TV). The fact is that in Germany the selected frequency sub-carrier 5.5 MHz sound, but it is 6.5 MHz. If You are the owner of such a vehicle and understand how to keep the soldering iron, you can implement the restructuring of the sound.
First you must find where is located the high-frequency Converter-naturally, it is there, and is stuck where RF cable (RF Out), so I think this problem will not arise.
Method one (the easiest)
Without opening the Converter, to try to gently twist the core of the coil that is responsible for the frequency of the sound subcarrier. Usually on the Converter there are two coils, one is used for tuning to a TV channel and one for the sound subcarrier. In front of the tuning circuit on the channel usually has a hole on the backside of the device and corresponding label (for example 21-49 Ch), indicating a limit in what you can rebuild the frequency of the video signal. Thus, the remaining circuit is the cause of no sound. Moreover, it is only similar to our conventional view of the circuit. Therefore, you should try to twist his core.
This method does not guarantee that you will be able to rebuild the VCR, but nevertheless its worth a try, good in my experience, there were two such cases in which it is managed.
The second way (a little harder)
If the above tip does not help, then proceed to the second part of the plan "Russification" of our apparatus. Typically, the cores for the coils of the circuits used ferromagnets, i.e., carbonyl iron or ferrite. Ferromagnets, as you know, lower the frequency of the circuit, and the diamagnetic increase. Thus, if you carefully Unscrew the native core and screw in its place a suitable brass or copper screw, that can be configured to receive sound.
The third way (rework)
If the second method did not meet Your expectations , we will have to make to all this soldering iron. First, you must determine how electrically interfaced Converter with a motherboard of the VCR. Most often, unfortunately, the Converter is soldered directly to the motherboard, so will have to carefully unsolder. For this I used a 60 watt soldering iron: Gulf fusible solder all the pins of the Converter, gently heated evenly all the contacts and try without too much force to pull the Converter module. Then braid remove excess solder and release the mounting holes. If the Converter communicates with the motherboard via a detachable connection, then consider yourself lucky, and a soldering iron while it is possible not to include.
Carefully remove the cover of the Converter, screw-back coil core and trying to find the capacitor circuit of the audio subcarrier. The capacitor is soldered parallel to the coil, so finding it is not difficult, but you have to make sure that it is the capacitor. If the tape is relatively old, the Converter most likely is made discrete, and because the capacitor there looks familiar. If there is a chip and wiring is made using elements of the mounting surface, we can proceed to the next item. Suppose You are lucky and the condenser looks like a normal capacitor, vypayayte it and read its value. Further, by the formula L=836/C [PF] find coil inductance [mH], then found on the basis of the inductance is determined by the capacitance of the new capacitor according to the formula C[pF]=599/1 [mH]. If the calculated capacitance values are not in range of capacitors, it is possible to make two or three connected in series or in parallel, in practice it is usually taken 1-3 pF is less than the calculated value. For example, in the VCR AKAI-VS9500 EG in the circuit stood native capacitor C31 33 pF. The calculation showed that it is necessary to replace it with a capacitor with a capacitance of 23 pF, leaving 2 pF for parasitic capacitance of installation. I put the composite capacitor of two series-connected (47 pF and 39 pF).
After that you can gently lightly solder the Converter unit to the place and try to adjust the rotation of the core it on sound subcarrier. After completing the configuration, you must insert the screens into place and safely solder the Converter as a whole (if it was sealed).
Somewhat heavier than is the case with the tape the last years of production, so that the installation carried out on the surface of the PCB. Marking of parts is often not available as such, and the Converter is assembled on a single chip, which is also sometimes without markings. Installation is dense, because it is likely to damage it (especially if with a soldering tip slips a drop of solder). As before, we have to start with the outline. There is usually a diagram is something like this (see pic).
Sometimes it is enough to unsolder the capacitor C2, and it is possible to achieve the appearance of sound the restructuring of the inductance of the coil, and if that doesn't work, then you need to unsolder the capacitor C1, and in its place solder mounted Assembly variable capacitor with a capacity of 10 pF/ 490 pF from handheld receiver and rotation on its own axis to catch the sound support. Sector overlapping plates to determine the approximate capacity required for the replacement of the capacitor.
If Your nastroeno-perestroika efforts You managed to post the circuit is broken, do not despair - it is enough to find the contour at 10.7 MHz, to convert it to 6.5 MHz and embed into the Converter (or get the circuit to 6.5 MHz from some repaired Your TV, then you don't have to count).
Purposely not using any references to chips and other items, I have not seen any scheme of the Converter except in [1], even in the native descriptions of tape recorders schematic of the Converter is represented by a rectangle with the inscription "RF converter".
Literature
1. Amateur radio operator. No. 1, 1991. S. 4-5
2. The reference book of the radio fan designer. Moscow. Radio and communication, 1990, edited by N. And. Chistyakova, S. 18-19.
Author: Oleg Agarkov, Khmelnitskiy; Publication: N. Bolshakov, rf.atnn.ru