Hello,
Radio transmitters going strong, good sound good range ! but have a different problem right now....
Ive been working on an 8 track player here, home unit, Panasonic. works fine but I noticed that when the unit was OFF and no tape in the player, the motor would STILL want to run and turn at very slow RPM, I checked the power switch, that had 0 resistance when off, so that wasent bad, its a micro switch,
I traced back the wires to the AC cord inside the player, one end goes through the power switch and the other connects to the primary of the power transformer.
One end of the line cord goes right into the primary of the power transformer. So basically the circuit is broken to turn power off on one side of the power line only.
Here is the part im not sure of, there is a device that says "PSR" looks like a squar about the size of a dime but square, says someting about 270 ohms on it with a + and - like temp coficeant perhaps, not polarity, and its connected across the switch, so by that I mean it is in the circuit all the time making a connection even when the switch is open.( unit shut off no tape in it.
To me this does not look like a surge protector or capacator for shunting inductive kick noise, it looks like just a resistor that keeps some voltage on the electronics all the time,(no remote control features ect) on the order of 1 Volt ( I measured it) Now this is not AC leakeage,I tested for that, this is voltage that goes through that device into the electronics when the main switch is off.
I sniped the wire on one end of the device it and then lost the constant 1 volt so the motor wont turn and the electornics were totally off.I confirmed with volt meter readigs.
I would like to know if anyone can tell me what this device is so if its leaky or faulty, I can replace it. Im not sure of the purpose of it but im sure there is a purpose !
I have seen devices like this that will reduce surge current to avoid large start up currents in older TVs but noting in small stuff like this tape player.
At any rate if any one is familar with this device let me knwo so I can track one down or at least find out what it is and if its suppose to have leakage like it does.
I dont have a schmatic of the tape player but its a model RS 804 US. its a player only model. After I cliped the leads on the part all is well and it dosent have any effect on pops on start up or when the tracks change far as electrical noise so not sure what the part is for, ( never did ) I would assume surge protection on start up but its in the circuit across the switch full time .
Radio Joe
Here is a link to a device which may be similar to what you have there: http://www.prisemi.com/UploadImage/files/PSR05.pdf
Looking at the schematic of the device, it's a bridge rectifier with a zener diode across the output.
If a voltage applied to the input of the bridge rectifier exceeds the zener voltage rating, the zener would conduct and shunt the high voltage, hopefully absorbing it without blowing up thereby protecting the switch from arcing.
This is a SWAG but could be similar to what you have there. Normally this device would look like an open circuit until the zener voltage is exceeded. The zener voltage of this device is only 6 volts but could easily be made to have a breakdown voltage above the normally applied AC voltage.
Joe, I think that is probably a power surge resistor sometimes called a snubber. These consist of a resistor and capacitor in series and are used to suppress sparking across switch contacts when they open. It could be that the capacitor inside shorted leaving only the resistance in the circuit.
If the R value is to be believed then you could possible make one with a 270 ohm resistor and perhaps a .01uF cap in series. The cap needs to be rated at 200 V or greater with most for 120 VAC circuits rated at 377V.
The thing which I find strange is that it has a + and a - on it though it is connected to AC.
Neil
Given the age of the player, I'd go with Snubber. I see these used in traffic signal cabinets across a variety of components like relays and switches. Their physical appearance are generally 3/4" x 1/2", looking like a moulded capacitor. They usually have a schematic marking showing the RC network.
But why put it over the contact from the microswitch?? It seems better to put it over the induction (eight track motor)!!
more than likely its a snubber, the diodes are on a power supply board so that wont be the part, the + and - apear to be more of a tolorance deal than indicating polarity. I see I can post attachments here including Jpegs, I have the player all put together now. I almost wore out the screws taking it apart and putting together last few times, but next time and there will be a next time, ill take a picture of it. Its about a bit smaller than a postage stamp squar and about 1/4 thick or so. My guess is snubber too, but it threw me that it conducted a bit but bet it has a small internal short like Neil says. I didnt ohm it out but when I cut one lead the problem was gone when the switch is off no power comes through. I did test the switch and no leakage there. As I said I cant hear any pops or anything when powering up or changing tracks, so I dont think any harm done having it disconnected for now. The device isnt actually soldered across the micro switch that switches AC on but is across the switch if you trace the wires back to the transformer, there is a solder lug there and thats where it is.
I have ohter players from the era I can check those too see if anything like that is on them. The player is a home player but uses a DC motor.
Thanks for all the input.
A side note, if you remember some time ago i had a post that I had tree FM transmitters using the BH 1417 chip ( 1415?) i get them mixed up, ok well this transmitter is full 88-108 so what ever that chip is.. well the three transmitters all had the same problem, wont transmit stereo.
I did trace out all wrireing on the boards, no mixing of the audio befor the inputs on the chip, I ended up changing the chip twice with two different sources for the chip and still no luck, they transmit the piolot 19 khz which lights up the indicator light but audio is in mono.
I pretty much gave us and worked with the guy in CHINA who sold them to me and he agreed to take a look at them.
I sent them back last week, so I suppose after the first of the year if they get there ill hear someting, hopfully STEREO ha ha
That one is a real puzzler... I suspect some compontent on the board isnt correct , I checked all the resistors but SMD caps for the most part arnt marked... I had coffe to drink here and transmtters readings to take no time to try to swap SMD parts ...
Ill let you know what the guy in china finds.
I have one other thing and should move this to proper post site, but on the TH transmitters, it seems if you really jam in the audio voltage, I can get the field strenght signal to really bounce positive, but have to drive the singal hard to do that... If im correct with all operating properly, signal strenght should be 50 % higher under modulaton peaks than dead carrier so i havnt checked with a scope to see if im over modulating,but audio on the car radio is much louder and nice and clear so I dont think I am.. Just wondering what the ohters have to say about this.
Radio Joe
Some years ago a popular brand of TV was having problems catching fire.
When shutting off the TV, the power switch contacts would arc and continue to arc until the control caught fire.
The fix was to put a snubber across the switch to prevent the arc.
Rob,
Good point since inductive components cause "kickback" voltages which can be clamped or suppressed st the source but even with a resistive load a switch contact will arc upon opening. This causes erosion of the contact surfaces so the intent of using a snubber is to reduce the arcing and hence reduce the mechanical damage to the switch. Placing the snubber across the load won't prevent the arcing so it is placed across the switch.
Microswitches have small contact area and will benefit from a snubber though I have rarely seen them used unless there is high inductance in the load such as with contactors or motor starters or telephone switchgear. Larger switches don't need them unless the design is for millions of make/break cycles such as in MRAM's example. A home appliance or electronic device switch will not need to withstand this many cycles. For example, washing machines are designed for 12,500 cycles which is considered the end of design life for this appliance. A stereo or radio on/off switch will probably not have many more cycles than this.
Neil
We hear a lot about the usefulness of replacing capacitors in older equipment.
After reading the foregoing I am also inclined to believe that adding a larger, heavier duty switch to electronic equipment would also be a good idea, mainly in equipment we want to keep alive.