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How to find the resistance of burned resistor?/Need help fixing my Hi-Fi Answered

I have ShockWave HI-FI Model: SW390 it had burned IC TDA2030, i replace it power it up and after few seconds of buzzing capacitor blew up and resistor burned. I don't know what caused to burn but i want to change them to repair it. I was trying to find datasheet about this HI-FI so i can see the components and what i need to replace but unsuccessful, the capacitor i was able to replace it, it was 10uF 50V i replaced it with 10uF 63V but i have problem replacing the resistor, i don't know what resistance it had. Can anyone tell me how can i find what resistance i need so i can replace it? What can caused blowing the capacitor and burning the resistor? (there was no shortage even if it was the fuses will burned before these components)

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2
Jack A Lopez
Jack A Lopez

Best Answer 12 months ago

I suggest drawing your own diagrams, since official ones cannot be found, at least for the areas surrounding where components have been burning and exploding.

I see the burned out resistor in your pictures, but I do not see the 10 uF (electrolytic?) capacitor you replaced. Were those two components near each other?

I am trying to guess at the function of the burned resistor. It is sitting in between those two really big electrolytic capacitors, on one side, and a little group of two zener diodes (labeled ZD1 and ZD2) and two small electrolytic capacitors.

My guess is that group, two resistors (R47 and R48), two zener diodes (ZD1 and ZD2) , and two small electrolytic caps, are there as a kind of crude, two sided, voltage supply for the nearby 8-pin IC, with 4558P printed on it, which is a dual op-amp.

If that guess is correct, my next guess is that R47 and R48 are twins, like two brothers, or maybe a brother and a sister. That is to say, symmetry suggests they are the same resistance, and same power rating.

Regarding resistance, both are likely 100 ohms (brown-black-brown), like we can see on the sibling that survived.

Regarding power rating, both are physically large. They look to be the two largest resistors on the board, in physical size. Maybe 1 watt or 1/2 watt, for R47 and R48?

In contrast, I think every other resistor on the board is a much smaller power rating, either a 1/4 watt, or 1/8 watt, with the physical size indicating which is which.

0
krstecd
krstecd

Answer 12 months ago

I replaced the burned resistor with 100 Ohm and it worked, but there is other problem now, from the subwoofer i just hear buzzing and from the speaker i hooked up, i need to get really close with my ear so i can listen anything. also when i turn on and off there is huge "knock" (i don't know how to explain but you can hear in the video)

Video where i turn On and Off and trying to find FM frequency and changing to aux (If you can't hear the buzzing try listen with headphones): https://imgur.com/a/kGXN806

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Jack A Lopez
Jack A Lopez

Answer 12 months ago

I am glad my hunch about the 100 ohm resistor, being one of pair, seemed to help.

I have listened to your video, and I hear the sounds you describe, but I do not yet know what it means.

Really, I do not yet have my head around this whole thing, to the extent I can picture, or correctly imagine, what is really going on.

Like I said before, I think the solution may lie in you studying this circuit more deeply, including drawing your own circuit diagrams, and studying the data sheets of these various ICs for clues about circuits they are typically used in, and maybe even doing some testing with your voltmeter, or oscilloscope, if you have one.

In fact you are, in many ways, more able to do this than others, since you have the artifact in front of you, while I (or anyone else reading this forum) have to just sort of glean what I can from pictures, and sounds, and words and stuff.

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krstecd
krstecd

Answer 12 months ago

Well thank you for the Resistor solution.
Now i think it might be problem with bad capacitor. I'm desoldering the capacitors (not all of them, just the bigger ones) to see if anyone of them have high resistance.

As i'm writing this i just found one El. capacitor with ESR=1.2 Ohm resistance. I don't have any capacitor with same resistance to replace it, i will buy them when i go to the store. (As much as i know that can be bad. I'm not a professional electronic technician, i just work this as a hobby because i like fixing and making stuffs.)

Again thanks for the help, i will try to see what i can do to fix it.

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krstecd
krstecd

12 months ago

Burned resistor is connected trough: Positive side of Bridge Rectifier -> Fuse -> Relay? -> Resistor -> Z.Diodes and so on.

The El. capacitor i replaced is on the other board where the Output/RCA jacks are.
In the photos i uploaded before on the photo with big IC you can see the El. capacitor on the right side of the board (blue capacitor) i replaced that one.

I will try to replace it with 100 Ohm resistor and update you what will happen.

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Jack A Lopez
Jack A Lopez

Reply 12 months ago

I guess I see the capacitor you replaced. It is the only blue skinned electrolytic cap, in a town full of black skinned ones.

Regarding what I was writing before about guessing about resistors, R47 and R48, and zener diodes , ZD1 and ZD2, and symmetry... I thought I would draw you a diagram of that. Also in the process of doing that I took the image of the bottom part of the board and flipped it over (mirrored it) so the circuit traces would be sort of laid out the same, as if I were looking at them, through the opaque board, from above. I inverted the colors too, just to remind us, we are looking at something somewhat fake by doing that.

Also I drew some little boxes, and circles in the places where I imagine some of the box shaped things {fuses, relay, bridge rectifier, mains power connector} and the circle shaped things{ big and small electrolytic caps} go.

By the way, I should mention, so far I have no good, like, causal explanation for why things are failing, in your amplifier circuit, in the sequence you describe. I do not yet comprehend the reasons why things are failing, or how these failures relate, or are causing, each other.

Honestly, I am hoping you can figure that out, mostly on your own... if solving the mystery is necessary to making the darned thing work again.

a-and-b-flipped-sides-together.jpgsw390-partial-power-supply-diagram.jpg