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Old 08-03-2020, 07:50 PM   #1
SluggerB
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Default Help diagnosing Pyle Receiver PTA66BT with burned resistors

Spoiler alert: I am a total noob at this, just getting into the hobby

My buddy has an audio receiver that stopped worked, everything turns on and functions but no sound comes out of any output (Speaker, AV, or Headphone) So I said I would take a look at it. I popped the cover off, and saw an obvious issue: One of the resistors on the board had burned up.

Photos:

Now I'm still learning but I know you need the color bands on the resistor to see what the resistance is, but the wrapping is burned off the resistor. The good resistor next to it is Brown-Silver-Brown which if I understand the mapping correctly would indicate a 180 Ohm resistor. So I bought myself a resistor pack off Amazon, and it showed up today. Unfortunately I didn't realize different resistors sizes exist and bought 1/4 watt resistors for what looks like a 1W resistor . But I popped a 180 ohm resistor in just to see what would happen, and predictably it smoked and burned up. I have ordered a set of 1W resistors that will be here in a few days.

I googled how to find the value of a burned resistor, and a PDF told me to measure from the leads to the end of the spiral grooves on the resistor, and doing that gave a value of 35 megaohms, I checked both directions and it read the same both sways. I don't think that's right.

I checked the big blueish resistors by the burned one, they all tested fine.

I followed the trace from the resistor back to the big caps over to the left on the photo, and saw it did connect to one of them. I unsoldered that from the board, and tried testing it a bit and it seemed to be OK. Just to check, I unsoldered another one of the big caps, and it tested identically, so I assume that would make it likely they were good.

I then followed the trace to the right, and removed the first capacitor that I came to. It was 45 mF at 35V, my capacitor pack had a bunch of 45mF caps but not 35V, so I put in a 50V since the internet told me it was OK. Flipped everything back on, still got a burning resistor.

I did try and test the zener diodes over to the right but I'm not sure if they are right. When I got negative terminal to the black lead and positive terminal to the red lead, i get an OL, when I switch the leads, I get readings, but I thought the opposite should happen?

I've gone over the board can't find anything else that looks faulty, none of the caps are bulging or leaked, the fuses all test fine, connections are all solid. Just shooting in the dark at this point and look for advice.

And yes, I am aware this is a $100 budget piece of equipment, I'm doing this for fun and to learn, it's a buddy of mines piece and he doesn't care what happens to it since it was already not working.

Thanks for any help!
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Old 08-03-2020, 08:05 PM   #2
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Can we see good clear straight shots of the whole board top and bottom side?
More likely there is shorted components so too much current flows through the resistor so the resistor burnt out.
The burnt resistor looks to be for dropping high Voltage to lower Voltage to run the pre-amp sections.
What is the are the color bands of the resistor next to it?
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Old 08-04-2020, 02:04 PM   #3
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Quote:
Originally Posted by budm View Post
Can we see good clear straight shots of the whole board top and bottom side?
More likely there is shorted components so too much current flows through the resistor so the resistor burnt out.
The burnt resistor looks to be for dropping high Voltage to lower Voltage to run the pre-amp sections.
What is the are the color bands of the resistor next to it?
I can try and take better photos tonight, smartphone is all I have. The resistor next to it is Brown/Silver/Brown which maps to a 180 Ohm resistor. I tried another 180 Ohm (but only 1/4 watt) and it burned up.

I did see a youtube video about a receiver with a blown fuse that traced the problem to the transistors. I think the transistors for this board are under that heat sink, I'll be removing that tonight and see what I see. If I do see them I will check the resistance across the collector and Emitter and see if anything looks off.

While I am checking for shorts, I would put my DMM to continuity, put the black to a ground on the board, and the red to the components along the path, right? Should the caps show continuity on both legs if they are working? Other folks seem to the think the short, if there is one, is on the side of the resistor opposite to that big capacitor bank. There aren't that many components there, so I could just start replacing them one by one, however I'd prefer to learn how to properly diagnose it vs just brute forcing it, since this is mostly a learning exercise for me.

Thanks for the reply

Last edited by SluggerB; 08-04-2020 at 02:11 PM..
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Old 08-04-2020, 04:19 PM   #4
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

that resistor may well be a different value than the one next to it ..
find whats shorted first unless you enjoy burning electronic components .
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Old 08-04-2020, 04:31 PM   #5
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

1) "The resistor next to it is Brown/Silver/Brown which maps to a 180 Ohm resistor. I tried another 180 Ohm (but only 1/4 watt) and it burned up." 180 Ohms color bands will be Brown Grey Brown.
2) Use the Ohm meter to check the resistance between GND and each legs of that 180 Ohms resistor, the do the same on the empty pads of the burnt out resistor.
3) As explained earlier, too much current was flowing through the resistor so the resistor burnt out , the cause of over current can be due to shorted components. Right now since I do not have good clear pictures of how that resistor is connected in the circuit so I can only guess that is for dropping the high Voltage to lower Voltage to run the circuit.
Those two resistors may be for the Plus and Minus regulated power supplies, I can see some Zener diodes and Transistors in the pictures.
BTW, you should attach the pictures using 'GO ADVANCED' to attach the pictures instead of 3rd party site.
Attached Images
File Type: jpg Hc8AUYo.jpg (382.5 KB, 6 views)
File Type: jpg I0KOXMl.jpg (419.8 KB, 7 views)
File Type: jpg LLyeiaO.jpg (826.5 KB, 14 views)

Last edited by budm; 08-04-2020 at 04:43 PM..
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Old 08-04-2020, 05:13 PM   #6
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

circuit diagram would help .
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Old 08-04-2020, 07:22 PM   #7
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Quote:
Originally Posted by budm View Post
1) "The resistor next to it is Brown/Silver/Brown which maps to a 180 Ohm resistor. I tried another 180 Ohm (but only 1/4 watt) and it burned up." 180 Ohms color bands will be Brown Grey Brown.
I tested it, it is 180 Ohms. You are correct, the other resistor could be different, I have no way of knowing. The wrapper was incinerated, and I can't find any schematic of the board. I emailed the manufacturer and asked them, and haven't heard back.

Quote:
2) Use the Ohm meter to check the resistance between GND and each legs of that 180 Ohms resistor, the do the same on the empty pads of the burnt out resistor.
OK I will try that and report back. Being a total noob, suggestions on what to use as a good ground? Does the device need to be plugged in?


Quote:
3) As explained earlier, too much current was flowing through the resistor so the resistor burnt out , the cause of over current can be due to shorted components. Right now since I do not have good clear pictures of how that resistor is connected in the circuit so I can only guess that is for dropping the high Voltage to lower Voltage to run the circuit.
Those two resistors may be for the Plus and Minus regulated power supplies, I can see some Zener diodes and Transistors in the pictures.
Yes, the burned resistor leads to three 8050 transistors and the good resistor right next to it leads to two 8550 transistors. There are zener diodes there as as well, I don't know what their presence would indicate


Quote:
BTW, you should attach the pictures using 'GO ADVANCED' to attach the pictures instead of 3rd party site.
Here's the back of the board, I marked the ends of the replacement resistor (where the original burned) in the picture.



Here is the board picture showing the transistor and capacitor I removed, in both cases the resistor still burned when the machine was turned on.




I did test all the main transistors and resistors attached to the heat sink. All of them seem to be good.

Quote:
circuit diagram would help .
Agreed, but I don't have one, cant find one online, and the manufacturer hasn't responded when I asked them for one.

Quote:
find whats shorted first unless you enjoy burning electronic components .
That's what I've been trying, I can't find anything yet, any tips of what or how to look would be much appreciated. so far I've only been cooking my same resistor I put in, when it starts to smoke I turn the unit off.

I'm thinking of removing the resistor so it doesn't burn up, turning the unit on, and starting at those blue wires measure for DC Volts and work my way across the board until I get a reading that looks wrong. If I plug the device in, how would I test the capacitors in a safe way to see if they are good? Should the volts across the ends match the volts going into the board?

Here is the datasheet for those power relays https://datasheetspdf.com/pdf-file/1...X202-S-124DM/1, using that info how would I test them? They are dealing with voltage big enough to fry a resistor so maybe one of them went bad?


One thing that puzzles me, most of the way I can trace to get to this resistor involve passing though an even smaller resistor. If enough power was going through those to burn the big resistor, wouldn't the smaller ones have burned up to?


Thanks again for the help. I am having fun

Last edited by SluggerB; 08-04-2020 at 07:38 PM..
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Old 08-04-2020, 08:19 PM   #8
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Based the pictures, those two resistors should be the same value.
So all you have to do right now is to check the resistance as I suggested, since you have the board out off the chassis then you cannot really use the chassis for GND ref. for the meter unless you verify that the circuit GND of the board still have GND connection to the chassis or not, so at this point you will need to use the board circuit GND which will be where the large filter cap negative of one cap joined to the positive leg of the other filter cap (the amplifiers use positive power supply and negative power supply to run) OR try using the Black speaker terminal for GND ref. for the meter.
The picture of the bottom side of the board is too blur for me to use to trace out the Voltage regulator section.
Since we do not have the schematic, all we can do is to trace out the circuit manually.
When perform resistance testing, do not apply power to the unit/circuit unless you want to blow up the meter and the circuits.

BTW, the white connector on the right side of the board has pin labels printed on the board. Can you zoom in so we can see what those pins are for?

"One thing that puzzles me, most of the way I can trace to get to this resistor involve passing though an even smaller resistor. If enough power was going through those to burn the big resistor, wouldn't the smaller ones have burned up to? " Unless you understand the circuit then it will not make sense to you right now.

Last edited by budm; 08-04-2020 at 08:31 PM..
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Old 08-05-2020, 05:13 AM   #9
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Thanks for that awesome write up, I will endeavour to check those resistences and see if I can get a better picture

That white plug runs up to the board with the controls for the unit on it. I will try and take a pic of the connector. I only have time in the afternoon to work on this so I will be posting nightly updates
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Old 08-05-2020, 08:29 AM   #10
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Quick update, I had a few minutes so I popped into the workshop and removed that cable connector from the front panel board, isolating the 2 boards. I then powered on the unit and got more smoke. Not sure if that tells us anything. I also took a few more photos I will post later


Quote:
Originally Posted by budm View Post
you will need to use the board circuit GND which will be where the large filter cap negative of one cap joined to the positive leg of the other filter cap (the amplifiers use positive power supply and negative power supply to run) OR try using the Black speaker terminal for GND ref. for the meter.
Can you clarify what a large filter cap is? Is that the bank of 6 large capacitors? I will look on the power plug and around that area for ground. I could also screw the board back into the chassis is that would give me a ground to use as well. I'll be messing with it tonight trying to get those resistor numbers and I will post more photos.


Also, I took a peek at that chip by the burned resistor with the heatsink with my new pair of magnifier goggles I just got, it has KA7805 written on it. I googled that and it says it is a "Linear Voltage Regulator" https://www.digchip.com/datasheets/p...161/KA7805.php

Since it is a voltage regulator right next to the resistor, maybe that went bad? The datasheet says it has several fixed output voltages, based on the model number it looks like this one is fixed 5V output, maybe I could turn the unit on and try to quickly grab a reading off the terminals and see if that is good. I am completely guessing that the component that failed and is burning the resistor is something power related. Is that likely or could a short in something completly unrelated to the power system be responsible? I'd also like to try and grab a voltage rating going to the burning resistor, I'm not sure how to do that, if I measure DC volts across the resistor I will get less than it actually is cause the resistor is still resisting something, right? Would removing the resistor and measuring the two solder points get me an accurate reading? I usually get around 5 seconds of power on time before the resistor starts smoking, and if it burns up totally I have more. I testing the thing after todays smoking and it's actually still testing good despite getting zapped everytime I test something by turning the unit on.

Definitely having fun learning!

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Old 08-05-2020, 08:36 AM   #11
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Quote:
Originally Posted by SluggerB View Post
I then powered on the unit and got more smoke.





.
what burned this time ?
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Old 08-05-2020, 11:12 AM   #12
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Quote:
Originally Posted by petehall347 View Post
what burned this time ?
Same resistor (the one I wired in). No other part has ever given any obvious sign of malfunction. Whenever I try a new power on, I turn the unit off when that resistor starts to smoke.

Better picture of bottom of the board



Picture of the labels next to the white connector



Does that "DG" mean it is a ground I could use to test?

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Old 08-05-2020, 04:04 PM   #13
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

1) The most important thing right now, do not power up the unit until we find out the cause of that made the resistor burnt out, we do not want to cause any more damages to the board.

2) As you can see, the pin labels for the connector show 5V (5V from 5V regulator 7805 IC), then you have +V and -V for the Plus and Minus power supplies as I explain earlier.

3) We need the resistance readings that I request, just use one of the speaker Black terminal/ or the solder pad of the black speaker terminals are soldered to as the GND ref. for your Ohm meter. We must have those resistance readings first.

Last edited by budm; 08-05-2020 at 04:08 PM..
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Old 08-05-2020, 05:00 PM   #14
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

out of interest what is printed on the 8 leg chip ? am thinking its an op-amp . maybe nothing to do with burnout .
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Old 08-05-2020, 06:47 PM   #15
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

BTW:
DG = Digital Ground
AG = Analog Ground.

Put the 7805 black in place, it is not being fed by the burnt out resistor.

Last edited by budm; 08-05-2020 at 06:54 PM..
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Old 08-05-2020, 06:56 PM   #16
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Quote:
Originally Posted by petehall347 View Post
out of interest what is printed on the 8 leg chip ? am thinking its an op-amp . maybe nothing to do with burnout .
It looks to be OP amp, pin 4 (-VCC) is fed by the -V regulated supply, pin 8 (+VCC) is fed by the +V regulated power supply.
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Old 08-05-2020, 07:11 PM   #17
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Why is this component removed?
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Old 08-05-2020, 07:15 PM   #18
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I need better focused pictures of the bottom side of the board, I get headache trying to trace out the traces.
Also need closed up pictures of this section, see attached picture..
Please make sure to do straight shots pictures of the board.
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Old 08-05-2020, 07:36 PM   #19
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Update: my 1W resistors showed up today, so I removed the 1/4th watt resistor. With it out, I turned the unit on and measured DC voltage across the pads and got 33.8 volts reading.

I then put the 1W 180 ohm resistor in place. I also put back the transistor and the capacitor so everything is back on the board correctly now.

I turned it on and while it took longer, the resistor did eventually start to smoke. I also grabbed a quick reading off that chip with the heatsink by it and got 26v, and it looks like a 25v chip, but I don't think that little extra power would burn up the resistor.

I tried using the black speaker terminal as ground and got nothing. I will try more spots and I will take more pictures. I thing imgur resizes them cause on my PC they are huge and you can zoom way in and see pretty clearly
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Old 08-05-2020, 07:42 PM   #20
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Default Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

1) Well, I told you not to power up the unit, you are just going to cause more damages. You are not going to listen, are you?

2) What Ohm scale of the Ohm meter did you set it to?

3) Measure the resistance between the speaker Black terminal (where the terminal is soldered to) and the AG pad of the connector, it should show < 1 Ohm.
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