Ok , so I have a lot to say after I spent 3 hours translating user manuals , service manuals and russian forums :
So , let's start with the beginning :
When I first made this thread , you posted a image highliting the flow of the audio from the deck
Very good representation but I noticed a mistake :
You thought that the M would represent a VU
meter , but this radio doesn't have a VU meter
What is it ? I made this schematic of the current flow that passes thru that "M"
high quality variant of the picture :
https://goo.gl/photos/wHnX2Lbw4vxBZfP89
So , as you may noticed , the M stands for `мотор` (MOTOR)
You can see what each of the symbols on the right do and why the motor is spinning (when pressed the play button) when the radio is on radio operation mode .
Also , you can see a green circle , inside it is the symbol for "recording" so you can easily assume that this is the record/play ganged switch .
Also , the biggest thing that you may have noticed are the two rectangles in the upper corner of the image
There is a pink one and a brown one :
The pink one is the
TAPE/RADIO GANGED SWITCH (we are gonna get to that later this post).
The brown one is the AUTO FREQUENCY CONTROL / LIGHT ganged switch .
Now , let's go to the recent mistake :
You assumed that YKB means tape ... Lets see what radio bands can this radio cassette receive :
ДВ 2000—740,7 м (150—405 kHz) ------------ Long Wave
СВ1 571,4—303,0 м (525—990 kHz) ------------ Medium Wave 1
СВ2 300,0—186,9 м (990—1605 kHz) ------------ Medium Wave 2
КВ52 75,9—52,6 м (3,95—5,7 MHz) ------------ 52 meters (Short Wave 1)
КВ49 50,4—48,4 м (5,95—6,2 MHz) ------------ 49 meters (Short Wave 2)
КВ41 42,2—41,1 м (7,1—7,3 MHz) ------------ 41 meters (Short Wave 3)
КВ31 31,6—30,7 м (9,5—9,775 МHz) ------------ 31 meters (Short Wave 4)
КВ25 25,7—24,8 м (11,7—12,1 МHz) ------------ 25 meters (Short Wave 5)
УКВ 4,56—4,11 м (65,8—73,0 МHz) ------------ FREQUENCY MODULATION (FM mono)
You see that YKB = FM band .
And also see that it can receive some parts of some radioamateur HF bands , 40meter and 60meter bands (As you were/are a ham radio operator after the 73 you have in your name) , but it can't receive SSB , it needs to be modded with a beat frequency oscillator .
It uses an older FM band , from 65 to 73 mhz , it's called the OIRT band , few eastern europe countries still use it , it was decommisioned in 1990's , now we use the CCIR band , from 88Mhz to 108Mhz .
More info about it (from Wikipedia) :
OIRT bandplan
The
OIRT FM broadcast band covers 65.8 to 74 MHz. It was used in the
Union of Soviet Socialist Republics and most of the other
Warsaw pact member countries of the
International Radio and Television Organisation in
Eastern Europe (OIRT), with the exception of
East Germany, which always used the 87.5 to 100 (later 104) MHz broadcast band—in line with Western Europe.
The
lower portion of the VHF band behaves a bit like
shortwave radio in that it has a longer reach than the upper portion of the VHF band. It was ideally suited for reaching vast and remote areas that would otherwise lack FM radio reception. In a way, FM suited this band because the capture effect of FM could mitigate interference from
skywaves.
Following the collapse of the communist governments in Eastern Europe, the 87.5 to 108 MHz band began to be adopted and is now in use in all those countries. This was prompted by the expansion of broadcasting and the modernisation of existing transmission networks, using new or second-hand transmitters from western countries,[
citation needed] together with a general desire for standardization with the West.
Many countries have completely ceased broadcasting on the OIRT FM band, although use continues in others, mainly the former republics of the USSR. The future of broadcasting on the OIRT FM band is limited, due to the lack of new consumer receivers for this band outside of Russia.
Countries which still use the OIRT band are
Russia (including
Kaliningrad),
Belarus,
Moldova,
Ukraine and
Turkmenistan.
Hungary closed down its remaining broadcast transmitters in 2007, and for thirty days in July of that year, several Hungarian amateur radio operators received a temporary experimental permit to perform propagation and interference experiments in the 70–70.5 MHz band.
In Belarus, only government-run public radio stations are still active on OIRT. All stations on OIRT in Belarus are a mirror of normal FM broadcasts. The main purpose of those stations is compatibility with older equipment.
In 2014, Russia began replacing OIRT transmitter with normal FM transmitters. The main reason for the change to normal FM is to reach more listeners.
Unlike Western practice, OIRT FM frequencies are based on 10 kHz rather than 50, 100 or 200 kHz multiples. This may have been to reduce co-channel interference caused by
Sporadic E propagation and other atmospheric effects, which occur more often at these frequencies. However, multipath distortion effects are less annoying than on the CCIR band.
Most stations on OIRT are broadcasting in mono although some stations are operating in stereo. Stereo is generally achieved by sending the stereo difference signal, using a process called
polar modulation. Polar modulation uses a reduced subcarrier on 31.25 kHz with the audio on both side-bands. This gives the following signal structure: L + R --> 31.25 kHz reduced subcarrier L - R.
The
4-meter band (70–70.5 MHz)
amateur radio allocation used in many European countries is entirely within the OIRT FM band. Operators on this band and the
6-meter band (50–54 MHz) use the presence of broadcast stations as an indication that there is an "opening" into Eastern Europe or Russia. This can be a mixed blessing because the 4 meter amateur allocation is only 0.5 MHz or less, and a single broadcast station causes considerable interference to a large part of the band.
The
System D television channels R4 and R5 lie wholly or partly within the 87.5–108 MHz FM audio broadcast band. Countries which still use System D therefore have to consider the re-organisation of TV broadcasting in order to make full use of this band for audio broadcasting.
Now lets understand how this radio switches between these radio bands
Let's start with something that you in your life always encountered :
A vintage Zenith black-and-white television , you might repaired dozens of them
What we need to inspect is how this tv switches its channels.
It uses a rotary band switcher to tune into the tv channels , as you know .
The soviets
copied this design and used it on almost all of their radios from 60s to 90s
Let's see how
the radio we are trying to repair switches its bands :
You need to rotate that button to switch the bands , just like in the vintage tv tuners
You can see the circuit boards for the tuner on the right corner of the whole schematic , the boards A3-1 A3-2 A3-3 A3-4 A3-5 A3-6 A3-7 A3-8 and A3-9 .
Each board has some pins or turrets or what you want to call them , that hit the other pins and form a connection when you switch the bands , these contacts are represented here (in a red rectangle) in this schematic :
Ok , now you understand how this radio switches his bands and how its motor is controlled .
Now our part of interest :
The tape / radio switch
First lets see where is located :
1 - Indicator for recording and the voltage of the batteries (red when batteries low)
2 - Indicator for power from AC line
3 - Tone control
4 - Volume control
5 - Cassette compartment
6 - TAPE/RADIO switch
7 - automatic frequency control switch in the FM range and the backlight scale
8 - fast foward
9 - play
10 - stop and release the cassette
11 - record
12 - rewind
13 - Radio strength bulb ( it lights up when it is tuned to a stong signal)
14 - band indicator
15 - telescopic antenna
16 - band switch
17 - microphone
18 - adjust frequecy button (change the frequency with it)
Now you also know how the radio looks from the front (on the back are just connectors)
The tape/radio ganged switch is highlighted better in the following schematic snippet :
Now , because every post has a question
This switch commutes a lot of little switches that change the audio signal and a lot of things (yellow rectangles and red lines , I may have missed some things)
Can I get the tape stage and radio stage working at the same time ? If so , how ? (Now that you know almost everything about this radio)
