Help diagnosing Pyle Receiver PTA66BT with burned resistors

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

So this is odd. I confirmed chips F and G and the CD IC are disconnected and drawing no power

So right now V- has chips A-E connected, and nothing else. It has 6.14v across the resistor

V+ has chips A-E connected, and the power LED. It has 6.2v across the resistor

Why is V+ resistor getting so much hotter than V- with such a minimal load difference? Do metal oxide resitors just run that much hotter than carbon film ones? Or is something else cause that V+ resistor to overheat? It can't be any missing connection or load or else we would see that in the voltage reading, correct?

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

So this is odd. I confirmed chips F and G and the CD IC are disconnected and drawing no power

So right now V- has chips A-E connected, and nothing else. It has 6.14v across the resistor

V+ has chips A-E connected, and the power LED. It has 6.2v across the resistor

Why is V+ resistor getting so much hotter than V- with such a minimal load difference? Do metal oxide resitors just run that much hotter than carbon film ones? Or is something else cause that V+ resistor to overheat? It can't be any missing connection or load or else we would see that in the voltage reading, correct?

The replacement is Metal Oxide type and has the same dimension as the MOX for the -V, correct?
Do you have infrared thermal meter?

https://www.electronics-tutorials.ws...tor/res_7.html

[Trumpetrousers]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Hi guys,

I've just joined this site. I enjoyed reading this a lot. I was so eager to do the repair myself...
I wanted to say the patience and effort given to help out the new chap was extraordinary. Medals should be awarded in some of these cases.

Well done to both of you for persevering and getting to the bottom of it.
Brilliant stuff.

Regards Martin.

[Trumpetrousers]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

PS This last bit is impossible ha, ha, this is great to read.
Is the DC voltage rock solid? Does it wiggle about at all? All I can think of is some ripple getting through or some AC component - Though it has multiple stages of filtering/regulation so don't see how.

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

The replacement is Metal Oxide type and has the same dimension as the MOX for the -V, correct?
Do you have infrared thermal meter?

https://www.electronics-tutorials.ws...tor/res_7.html

The replacement V+ is metal oxide (bluish color). The V- (and the original V+ that burned up) are carbon film (beige) color. It is the same size and tests same resistance

I do not have an IR thermal meter, just a hand held temp probe

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

PS This last bit is impossible ha, ha, this is great to read.
Is the DC voltage rock solid? Does it wiggle about at all? All I can think of is some ripple getting through or some AC component - Though it has multiple stages of filtering/regulation so don't see how.

The voltage drop across the resistor is solid. Probing other components with smaller contacts sometime I get wiggle in the numbers

It's just odd that 2 voltages so similar would produce such drastic temp difference's in the resistors. The carbon film V- resitor never even gets warm, the V+ gets to around 98-100 degrees and hot to the touch with just a tad more voltage going through it

The 2w resistor shows up tommorow so we'll see how that feels. I'm going to out it in first with just chips A-E and LED connected, get a voltage and temp, then add the 100ohm resistors and get a voltage and temp, and then the CD IC and get a voltage and temp

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

The voltage drop across the resistor is solid. Probing other components with smaller contacts sometime I get wiggle in the numbers

It's just odd that 2 voltages so similar would produce such drastic temp difference's in the resistors. The carbon film V- resitor never even gets warm, the V+ gets to around 98-100 degrees and hot to the touch with just a tad more voltage going through it

The 2w resistor shows up tommorow so we'll see how that feels. I'm going to out it in first with just chips A-E and LED connected, get a voltage and temp, then add the 100ohm resistors and get a voltage and temp, and then the CD IC and get a voltage and temp

It will help if you leave the resistor legs long so the body of the resistors will be above the board for better cooling.
You can also try swapping over the 180 Ohms resistors.

[R_J]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

The V+ is likely used to supply more components in the circuit, the V- could be just for any of the opamps only.

[petehall347]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

is the board good for a 2w resistor in case of fault conditions ? like is there enough copper ?

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

The V+ is likely used to supply more components in the circuit, the V- could be just for any of the opamps only.

It does, but right now those extra components are disabled, I confirmed with my meter they are not drawing any voltage. At the moment the only difference in load between V+ and V- is the LED light.

I don't know if just the existence of a third transistor on that V+ power rail would cause that resistor to run hot.

is the board good for a 2w resistor in case of fault conditions ? like is there enough copper ?

I have no idea how to test that. Larger resistors do exist in the board in areas outside the power rails.

[petehall347]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

you are like doubling the size of a fuse . if downstream things can cope with this thats fine . some things are built right on the edge of everything .unlike the in the old days when everything was overrated .
there are probably guidelines around that say what current can pass through copper safely . i dont have a clue as never designed a circuit board .

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

BTW, the MOX can handle high temperature than Carbon film.
So did you swap the 180 Ohms resistors?
You can also see surface temperature rise chart (MO-MOX PDF) that 1W MOX at 50% of power rating, the surface temperature rise is 37.5c = 99F temp rise above ambient temperature..

So you have Vdrops of 6.2V on 180 Ohms resistor, so power dissipation is about 0.2Watts, according to the chart, the temp rise at 0.25Watts is about 22c = 72F temperature rise above ambient temperature.You indicate 100F reading? if ambient is 25c (77F) then you are way below the rating.

Not many companies publish surface temperature.
I am still looking for Carbon film surface temperature rise rating.

Learning about resistor:
https://eepower.com/resistor-guide/

https://eepower.com/resistor-guide/r...ilm-resistor/#

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

you are like doubling the size of a fuse . if downstream things can cope with this thats fine . some things are built right on the edge of everything .unlike the in the old days when everything was overrated .
there are probably guidelines around that say what current can pass through copper safely . i dont have a clue as never designed a circuit board .

Question, I thought the same amount of current was going through the resistor, and the resistance is the same (180 Ohms) so the same amount of power is being sent down the rail. But the 2W resistor can dissipate heat faster. Are you saying the 2W resistor will allow more voltage to flow through V+ rail vs the 1W one? Or that of there was some sort of power surge, it would be able to withstand that better, and not burn out, and it would pass that excess power down the rail?

BTW, the MOX can handle high temperature than Carbon film.

I did read that metal oxide resistors can tolerate a higher temperature, but I don't know if it normally runs hotter under the same load compared to a carbon film one.

So did you swap the 180 Ohms resistors?

The 2W resistors show up tomorrow. The only replacement is the original repair replacing the burned up 1W 180 Ohm Carbon film resistor with a 1W 180 Ohm Metal Oxide resistor. I guess I could swap the V- carbon filter resistor with a 180 Ohm metal oxide resistor and see if that gets hot. I have 9 of them

You indicate 100F reading?

Well, around 100F is when I stopped measuring and turned the machine off.

according to the chart, the temp rise at 0.25Watts is about 22c = 72F temperature rise above ambient temperature. if ambient is 25c (77F) then you are way below the rating.

The room I am working in is about 64F-68F. Yes, I love the cold. So would that mean that the normal operating temp for that resistor would be 141F-145F?

Not many companies publish surface temperature.

Yeah I had little success finding any of that as well

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

So looking at https://cdn.badcaps-static.com/pdfs/...eef2e50ff9.pdf (I don't have this brand but I'm assuming different brands will not have wildly different properties) the Thermal impedance (°C/watt) for a 1W resistor is 110. Does that mean the temp rise of 0.25W would be ((110 * 0.25) * 9/5) + 32 = 81.5F? If so I am over that temp already.

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

It's the temperature rise, so if your room is 70F and the resistor is at 100F that means the temp rise is only 30F well below the expected which is good well within safe limit of the rating.
And if you raise the body above the board that should help cooling, it is not good idea to mount power resistor against the board.
So 25c (77f) ambient + 27.5c (81.5f) rise = 52.5c (126.5f).

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

It's the temperature rise, so if your room is 70F and the resistor is at 100F that means the temp rise is only 30F well below the expected which is good well within safe limit of the rating.
And if you raise the body above the board that should hep cooling.

I'm going to do that with the 2W resistor, I'm going to keep the legs a little longer, and I'm putting a piece of heat resistant tape on the board under the resistor. I've hit that stuff with 350 degree hot air and it didn't even crinkle.

And worse case scenario, since you have to buy all these things in batches, I have enough spare parts to completely replace the V+ power rail 7 more times lol

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Is your meter True R.M.S? If it is, set the meter to AC Volt then check the Voltage of each legs of 180 Ohms resistors against Ground.

[Trumpetrousers]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Budm has given unfailing good advice.
It is always good practice to raise power resistors off the board. It was very common to see this in the through hole era and further back.
No need for any fancy tape though.
Resistors convert electrical energy to heat with 100% efficiency whether they are carbon or metal oxide. The area of dissipation is the most critical, if they are of the same size they should get equally hot if the same value. (Though I should look at Budm's temperature chart before saying that...Though the physics say I ought to be correct). Ie. Metal Oxide resistors can be smaller as they can withstand more heat.
It is much more sensible to replace these with a 2W and not worry about the board or downstream components, If enough current is flowing to destroy a 1W, then everything will have suffered enough never mind before you get to the amount needed to frazzle a 2W. With the same logic, these are not intended as a fuse apart from a pretty poor one.
So in conclusion if they are dissipating a certain wattage, and both are very close to the same, then that wattage is all turned to heat, the surface area and the thermal resistance of the component to ambient along with airflow will determine the body temperature. Both should be very similar...

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Is your meter True R.M.S? If it is, set the meter to AC Volt then check the Voltage of each legs of 180 Ohms resistors against Ground.

It is not

The 2W resistors showed up, I will be putting it in this evening. My big worry is that the one pad is a little damaged so it will be tricky to get it in without causing further damage. I am going to melt the solder but not suck it off, while meted pull the leg of the 1W resistor out, and then insert the leg of the 2W resistor in, leaving a lot of height from the board. I figure the tape can't hurt since that spot on the board is already charred black. I ave been doing some reading and it does look like you can go arbitrarily large on a resistor value and be fine barring edge issues like impedence and such.

I also noticed there is a fan in the unit, but I have never seen it run. I don't know if it is actually hooked up to a thermistor or any kind of sensor, from memory it looks like it is just running right from the power supply and so should be spinning all the time. I will take a look, I have a bunch of old PC fans I could replace it with if it went bad, I have plenty of experience working with those from my building PC days.

After I replace the resistor I'm going to reattached all the pulled component so the unit is fully functional and try playing music on it for a solid 30 minutes and see if it can take it. If so I will consider the project finished and a success. If something breaks, I will report back

[Trumpetrousers]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

You can always scrape a bit of the green resist off the track to get more copper area to solder to.