it does have sentimental value to me and also is a project for me to learn how this works xdd thats all
The blue wires are the bases of the output transistors. On the diode scale of your meter blue-red (B-C) should be 550-700, also blue-white (B-E) with the plus of the meter on blue. Should be 9999 or ---- backwards. If your DVM doesn't have diode scale, 2000 ohm scale got those numbers on my 1990 meter. DVM post 2015 seem to have test voltage of <0.5 volts on 2000 ohms scale which will read ----- both ways (useless).
The resistors with coils around them should read 0. With the coil disconnected they should read about 0010, or 010.0.
They are rather low wattage for this position, and if you replace one, use a 3 watt or 5 watt wirewound resistor.
The red-red-brown resistor that reads 330 ohms, that is not optimal but not wrong enough to prevent sound from getting out. Could be a bad solder joint, this board is probably built by a hobbiest. Reheating can correct that.
I like revamping products made or assembled by free citizens. Every Class D amplifier was made in a country of serfs that has nuclear missiles aimed at me, which is grabbing shared resources (fish, oil) from neighbors in a nearby sea, and imprisoned 2 million people 2018 for looking like 60 criminals. Also Class D boards & IC's were made there. This board was likely made in Europe and the transistors in Europe also. If eastern Europe, those countries are now free.
The entire consumer electronics market is now dominated by entities that design products to fail in 3-5 years. Industrial grade amplifiers with 8-12 year life are now made, but you will only find some of them discussed over on PA thread. You will not find industrial grade products in the 50 watt market. If you really want 50 watts out of this for more than a few seconds, you will put heat sinks on the driver transistors and the VAS transistor. My 60 w/ch dynaco ST120 came with heat sinks on the drivers.
The resistors with coils around them should read 0. With the coil disconnected they should read about 0010, or 010.0.
They are rather low wattage for this position, and if you replace one, use a 3 watt or 5 watt wirewound resistor.
The red-red-brown resistor that reads 330 ohms, that is not optimal but not wrong enough to prevent sound from getting out. Could be a bad solder joint, this board is probably built by a hobbiest. Reheating can correct that.
I like revamping products made or assembled by free citizens. Every Class D amplifier was made in a country of serfs that has nuclear missiles aimed at me, which is grabbing shared resources (fish, oil) from neighbors in a nearby sea, and imprisoned 2 million people 2018 for looking like 60 criminals. Also Class D boards & IC's were made there. This board was likely made in Europe and the transistors in Europe also. If eastern Europe, those countries are now free.
The entire consumer electronics market is now dominated by entities that design products to fail in 3-5 years. Industrial grade amplifiers with 8-12 year life are now made, but you will only find some of them discussed over on PA thread. You will not find industrial grade products in the 50 watt market. If you really want 50 watts out of this for more than a few seconds, you will put heat sinks on the driver transistors and the VAS transistor. My 60 w/ch dynaco ST120 came with heat sinks on the drivers.
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yes you are right for it it is made in europe someone made it for my grandpa long time ago. btw i checked all resistors measured them and also checker color code on internet with the calculator and it seems like all of them are fine only wound ones i cant tell really. also they are only one that burned. i mean under them on the pcb is all black so i dont really know what to do now, i can power amp on , i did not do it for 2-3 years, all i did now is measuring it powered off should i power it on to check what is going on ?
i used this website to check color codes on resistors its easy and simple just what i need xd https://www.digikey.com/en/resource...ors/conversion-calculator-resistor-color-code
on my meter i have a diode symbol so it is that. also i will record a video measuring transistors as you said and you can tell me it it looks right
After doing the output transistor check, if good you may power up through the incandescent bulb accessory described earlier. A 60 w tungsten bulb series the AC input. Because of the high voltage, and the tendency of stranded wire to pop off the screws of light bulb base, I have my light bulb mounted inside a grounded steel box, with holes to see the light of the bulb. It also has a circuit breaker.
You could also test the 1 cm diameter transistors with diode scale. Base is the pin in the middle.
The burned looking resistors with coils over them, if still good, were too small in wattage rating. Installing 5 watt wirewound 10 ohm resistors in those position will stop the burning of the pcb.
Sorry, my US assembled computer locks up the browser if I view videos.
Before you test voltages on a powered up amp, you need an alligator clip lead to connect the DVM minus to the power supply ground, or speaker ground. Measuring voltage >25 with two hands risks stopping your heart as current flows from one hand to the other. No metal (jewelry) on hands wrists or neck. Wear cheap safety glasses, parts explode sometimes.
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Light bulb goes series the mains. My light bulb box has an AC socket on the surface. I cut the round hole in the metal with 2 mm drills, then connect the dots with a carbide (stanley) hack saw. Use safety glasses using power tools like a drill. Hand crank drills can sometimes be bought for E2 at flea markets. Stanley made one, also others. The power cord for the light bulb box has a standard cord & plug, usually salvaged from a dead appliance. The 6 amp (or 3 amp in Europe) circuit breaker before the light bulb socket I usually buy from a surplus house. The steel case goes to the safety ground pin in case a wire pops off the socket and touches the case. In that circumstance the circuit breaker will blow.
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i will not power it today, i will just check transistors and thats it. also is it possible to add some resistors in parallel with ones that are wound and if so what walue should it be ?
You need to disconnect the coil from one end of the output resistors, to measure resistor open or just too hot. 2 to 10 ohms is okay. As I said the output resistors are too low wattage IMHO. The coil appears to be just some hand wound wire, nothing special. 11 to 14 turns is the usual coil, which prevents AM and police/fire/CB/ham radio from leaking into the feedback line to the input transistors. My ST120 has the 11 turns wire wound around the speaker capacitor (which also works to block radio interference).
i did transistor measurements i will upload video to yt as private and send you link so you can check. and don't laugh hard hahahaha xddd
I only watch videos on television. If you manage to get this on NBC or PBS network, I might see it. (ha!) This computer is obsolete.
Judge whether transistors are 550-700 millivolts forwards (on diode scale) and 9999 or ---- backwards on b-e and b-c, and obtain replacements as necessary. The PNP transistors, as the driver closest to the ground rail, (emitter towards ground) are backwards from the NPN 2n3055 ones.
Judge whether transistors are 550-700 millivolts forwards (on diode scale) and 9999 or ---- backwards on b-e and b-c, and obtain replacements as necessary. The PNP transistors, as the driver closest to the ground rail, (emitter towards ground) are backwards from the NPN 2n3055 ones.
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btw on my multimiter i have resistor tester it is for small transistor but i wonder can it work on bigger ones ?
btw i dont uderstand that if i use 10k resistor do i have to wound coil on it or just 10k is enough ?
Diode scale works on both diodes, silicon and germanium transistors. It will usually not work on LED's, or double diodes (stabistors) used in some temperature sense features.
The output of a low power transistor amplifier is usually a 10 ohm resistor with a 8-14 turn coil parallel to it or wound around it. The coil has a usual diameter of 8mm to 13 mm. AA battery or china marker are usual winding forms. 300 watt or bigger amplifiers sometimes use a lower value resistor.
Per post 79 the arrow pointing at a line is the diode scale. The line refers to the line on the diode, which s the negative end. You will notice the transistor symbol on schematic diagrams has an arrow on the emitter leg. Arrow points from base to emitter on npn transistors, and base to collector goes the same direction. PNP transistor is opposite polarity, with the negative power supply connecting to the collector.
It is about 4 AM in eastern europe, right? I am about to get away from the computer for 16 hours. Happy hunting.
Per post 79 the arrow pointing at a line is the diode scale. The line refers to the line on the diode, which s the negative end. You will notice the transistor symbol on schematic diagrams has an arrow on the emitter leg. Arrow points from base to emitter on npn transistors, and base to collector goes the same direction. PNP transistor is opposite polarity, with the negative power supply connecting to the collector.
It is about 4 AM in eastern europe, right? I am about to get away from the computer for 16 hours. Happy hunting.
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