Help diagnosing Pyle Receiver PTA66BT with burned resistors

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I put my multimeter to DC Volts for this measurement.

Across the resistor on the V+ rail, I got 2.02V
Across the resistor on the V- rail, I got 2.03V

Black probe on the marked side, Red probe on the unmarked side: 7.56 kilo ohms
Red probe on the marked side, Black probe on the unmarked side: 8.9 kilo ohms.

9.8 kilo ohms

1) Voltage and current on 180 Ohms resistors for +12V and -12V test results.
Across the resistor on the V+ rail, I got 2.02V = about 11mA = 22mW.
Across the resistor on the V- rail, I got 2.03V = about 11mA = 22mW.

2) Lift one end of each 47 Ohms resistors that feed +/- 12V to OPAMP A ~ E, this will isolate the OPAMP A ~ E from +/- 12V power supply, so the only loads we have will be OPAMP F ~ G, CD IC, and LED indicator lights. See picture attached.

3) Keep the meter probe on the 180 Ohms resistor feeding the +12V circuit so we can monitor the current.

4) Plug the unit into the outlet strip that have power switch so you can quickly kill the AC to the unit if the resistor gets hot again.

5) Power up the unit while watching the Volt meter and see if the resistor still get very hot or not, then turn off the unit then we can calculate the current flow through the 180 Ohms resistor.

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Ok will do. One quick question though, since the 47ohm resistors are the first thing the V+ and V- got to from the plug, would interrupting them break the connection to all the components, not just chips A-E? Or are the other components feeding off another line?

Once I lift those resistor legs, if the power board resistor doesn't get hot, are there any other measurements I can make in addition to the ones you asked for in order to see if chip F, G and the CD chip are getting power? For the led light I can just see if it is illuminating it not.

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Lift one end of each 47 Ohms resistors that feed +/- 12V to OPAMP A ~ E, this will isolate the OPAMP A ~ E from +/- 12V power supply, so the only loads we have will be OPAMP F ~ G, CD IC, and LED indicator lights. See picture attached.

Done. See image

Power up the unit while watching the Volt meter and see if the resistor still get very hot or not, then turn off the unit then we can calculate the current flow through the 180 Ohms resistor.

I'm assuming you wanted me to plug in the front board. I did so and turned the unit on. The resistor on the V+ line measured 7.95 volts. I also took the same measurement across the V- resistor and got 3.68 volts. I took each reading multiple times.

The V+ resistor warmed up slowly, but did eventually get hot. I took out my temperature probe and measured it to around 105 degrees F and climbing before it started getting pretty hot to the touch so I killed the power. One thing to note is that the new 180 ohm resistor I put in is a blue one vs beige, which Google tells me is metal oxide and might just naturally run hotter during normal operation, I don't know.

I should note also that the power LED did in fact light up, so it is not getting it's power from the V+ line

After the resistor cooled down (it seems to have a resting temp of around 78 degrees when the unit is plugged in but not turned on), since I have a good 30 seconds before it gets hot, I quickly turned it on and took other measurements

Chip A-E measuring ground to VCC+ and ground to VCC- showed no voltage (just background reading from the meter) so they are definitely not getting any power.

Chips F and G measured around ~11 volts on VCC+ and - ~11 volts on VCC-, so even with those resistors pulled they are still getting power.

The CD chip measured 5.19 Volts from ground to pin 1 (VCC) so it is still getting power with the resistors pulled

Would that indicate that the root cause is one of those 3 chips?

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

"I'm assuming you wanted me to plug in the front board. I did so and turned the unit on. The resistor on the V+ line measured 7.95 volts. I also took the same measurement across the V- resistor and got 3.68 volts. I took each reading multiple times."

So now the 180 Ohms resistor feeding the V+ (+12V regulator circuit) has current draw of 7.95V/180 Ohms = 44 mA, so it went up from 11mA to 44mA (the loads are the F ~ G OPAMPs, IC CD, LED), four times as much so the resistor is now dissipating about 0.34W.

the 180 Ohms resistor feeding the V- (-12V regulator circuit) has current draw of 3.68V/180 Ohms = 20 mA, so it went up from 11mA to 20mA (the loads are F ~ G OPAMPs, which means they are drawing about 9mA (4.5mA per OPAMP), only twice as much, the resistor is now dissipating 0.074W.


The +/- 12V are spitted up to feed many circuits.

The +/- 12V is fed to 47 Ohms resistors to feed the Voltage to run A ~ E OPAMPs circuit, so when you lift those two 47 Ohms resistors, the A ~ E no longer have Voltage to run so they do not draw any current from +/-12V.

The +/-12V is fed to the 100 Ohms resistors to feed the Voltage to F ~ G OPAMPs, so they are still drawing current from +/- 12V because we did not lift the resistors.

The +12V is fed to the 510 Ohms resistors (IN PARALLEL) to feed the Voltage to CD IC, so it is still drawing current from +12V because we did not lift the resistors.

The +12V is fed to the resistors to the LED indicator.

Next step is to lift up the two 100 Ohms resistors that feed the +/-12V to F ~ G OPAMPs, then measure the Vdrops on the 180 Ohm resistors again. See attached picture.

Do not put the 47 Ohms for the A ~ E OPAMPs back in yet.

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I disconnected those 100 Ohm resistors (and left the 47 ohm resistors disconnected) and then powered the unit on and checked the voltage. The 180 Ohm V+ resistor was reading 6.25v. The 180 ohm V- resistor was reading 2.01v. I checked the voltage from ground to the VCC+ on chips F and G and was still getting ~11 volts. So I desoldered the other end of the 100 ohm resistors and removed them completely, and then the VCC+ of chips F and G weren't showing anything other than meter noise. I then rechecked the resistors and they were the same, 180 ohm V+ resistor read 6.25v, 180 ohm V- resistor reading 2.01v

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Also (since I'm starting to see where this is headed) looking at the bottom of the board there seem to be 5 components connected to pin 1 of the CD chip. A zener diode, 2 resistors, an electrolytic capacitor, and what I am guessing is a ceramic capacitor. Here are close ups of the top and bottom

[petehall347]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

check diode and caps for short .

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

check diode and caps for short .

That's a continuity check between the legs of those components right? If there is continuity that indicates a short? Or do I check each leg to ground?

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I disconnected those 100 Ohm resistors (and left the 47 ohm resistors disconnected) and then powered the unit on and checked the voltage. The 180 Ohm V+ resistor was reading 6.25v. The 180 ohm V- resistor was reading 2.01v. I checked the voltage from ground to the VCC+ on chips F and G and was still getting ~11 volts. So I desoldered the other end of the 100 ohm resistors and removed them completely, and then the VCC+ of chips F and G weren't showing anything other than meter noise. I then rechecked the resistors and they were the same, 180 ohm V+ resistor read 6.25v, 180 ohm V- resistor reading 2.01v

So without any resistors connected to the A ~ G OPAMPs +VCC/-VCC.

The 180 Ohms resistor feeding V- (-12V regulator) the current through 180 Ohms for the V- (-12V) went back down to 11mA as expected, due to NO loads from OPAMPs.

The 180 Ohms resistor feeding V+ (+12V regulator) the current through 180 Ohms (IC CD and LED are only two loads) is 6.25v /180 Ohms = 35mA, so it went from 11mA to 35 mA, about 24mA increase..

Right now we know this:

1) IC CD and LED draw 24mA from +12V power supply.

2) OPAMPs F & G draw 4.5mA each from +12V power supply.

Next:

1) Remove the two 510 Ohms resistors feeding the IC CD.

2) Put the two 47 Ohms resistors for the A ~ E OPAMPs back in place. DO NOT put 100 Ohms resistors back in place.

3) Measure the Voltage drops on 180 Ohms resistors again, this will tell us how much current A ~ E OPAMPs draw.

4) Measure the Voltage between Ground against each end of the 180 Ohms resistors.

[petehall347]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

That's a continuity check between the legs of those components right? If there is continuity that indicates a short? Or do I check each leg to ground?

check right across them .. power off of course doing resistance tests . i do a lot of my testing power off to look for shorts . checking current on current limiter resistors ends up in same place so long as nothing smokes whilst checking .

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

check right across them .. power off of course doing resistance tests . i do a lot of my testing power off to look for shorts . checking current on current limiter resistors ends up in same place so long as nothing smokes whilst checking .

Power off, none of the components shorted between their 2 legs

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I removed the two 500 ohm resistors. Just for kicks I turned the unit on and confirmed the V+ resistor is now reading 2V. I then soldered back in both 47 Ohm resistors. I turned the unit on and got the following readings

V+ 180 Ohms resister: 6.17v
V- 180 Ohms resistor: 6.11v

GND to V+ 180 ohm resistor leg farthest from ribbon cable: 33.2v

GND to V+ 180 ohm resistor leg closest to ribbon cable: 27v

GND to V- 180 ohm resistor leg farthest from ribbon cable: 33.3v

GND to V- 180 ohm resistor leg closest to ribbon cable: 27.2v

Sadly, the V+ resistor started heating up again, it got hot to the touch around 98 degrees F so I killed the power. I do not know if that indicates a fault or if metal oxide resistors just run that much hotter normally

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

OK, based on all the readings the component are not drawing excessive current sitting at idling stage with no signal applied:

Each OPAMP draws about 4.5mA, so 7 OPAMPS the total current draw is 4.5mA x 7 = 31.5mA. Input Voltage to 180 Ohms resistors about 33V (it will go higher if AC line goes higher).

If all resistors are put back in back in place, below is what you will see.

1) V-: the idling current for the -12V is 11mA, the current draw from 7 OPAMPs is 31.5mA, that means you will have 11mA + 31.5 = 42.5mA flowing through 180 Ohms resistor (Vdrops of about 7.65V), which mean the power dissipation for the resistor will be about 0.32 Watts, so 1 Watt resistor is not running hot and it rated at 3 times the power dissipation, so that is fine.

2) V+: the idling current for the +12V is 11mA, the current draw from 7 OPAMPs is 31.5mA, that means you will have 11mA + 31.5mA = 42.5mA, then add 24mA of current draw from the IC CD and LED, so the total current flowing of 66.5mA through 180 Ohms resistor (Vdrops of about 12V), which mean the power dissipation for the resistor will be about 0.80 Watts, so 1 Watt resistor is going to be hot, the resistor should have been rated at 2 Watts. The 3 Transistors connected in parallel has Vdrops between E and C is about 9V s0 power dissipation is 9V x 55.5mA = 0.50W, since Transistors are directly connected in parallel without any balancing resistors, some may conduct more than other so one may get real hot so it conducts more and goes into thermal runaway and other will then conduct less and less, it is bad thing to do unless you match all 3 Transistors spec.

My conclusion: the 180 Ohms resistor for the V+ should have been rated at 2W, the resistor will still get hot dissipating 1W of power but it will be fine since it will have more safety margin. The regulator circuit needs to be improved that means redesigning or replaced with IC regulator with proper heatsink and have at least 40V input Voltage rating and 0.5A current rating.

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

You know what, I think I actually understand that, so I learned a lot! Basically the unit was designed with a V+ power rails that is running near max capacity all the time and thus suceptible to burning up. The 1W resistor is going to need to handle 0.8 watts which means it will run hot and the transistors are near the peak of what they can handle so any slight surge in the AC line could fry either of them. So is the final analysis that there is no faulty component on the board, it was just designed poorly in a way that was prone to failure?

I am willing to put a 2W resistor in the V+ line, I'm not willing to redesign the voltage regulator. If I solder in two of the 1W resistors in the same through hole, will they share the load and each dissapate 1/2 the heat but retain a 180 ohm resistance? I could also try and rig up some sort of heatsink for it.

If this is indeed the end of the line, then a massive thank you to budm for all the work and education!

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

What of I remove that IC chip? It looks like an "Echo processor" and there is an echo button on the reciever to be used with the mic in, but this unit will never use that feature it will purely be used to play FM radio and Bluetooth. That would reduce the demand in the V+ line. Would that help? I could also remove the resistor feeding the led, the unit would be in a closet so no one sees it anyway.

Also, I see that pushing 0.8W through a 1W resistor will definitely heat it up, but now that I have replaced the shorted transistors, will it actually work assuming steady AC voltage?


What I am thinking is disconnecting the CD chip and removing the resistor feeding the LED and keeping the 100 ohm resistors feeding F and G disconnected, at that point V+ and V- should have the same load, and see what the 180 ohm resistor does then

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

Actually instead of two 180s I would need two 360s. And that's why budm told me to remove the two 500's even though they tested as 250s in circuit. I'm learning!

What I don't know if 2 360's would share the heat dissapation or not

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I disconnected the CD IC and hooked all the front boards backed up and can confirm the device does play music. After a minute it so the V+ resistor does got hot to the touch, but there is no smoke, no burned resistor smell, and it worked

I'm going to buy some 2W resistors, put that in and try not to destroy that one pad, then reconnect all the detached parts, and call it a job. Tons of thanks again for the help budm!

I am curious though, right now The only thing the V+ rail is supporting besides chips A-E is the LED light. Yet the V+ resistor is is still getting hotter than the V- resistor. So what is telling the syste to push more power through that resistor? Are the 3 transistors are always going to pull that 0.8W across that resistor, regardless of what is actually connected? If that is the case, then why aren't they doing that with the front board removed? Just for my education.

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

I disconnected the CD IC and hooked all the front boards backed up and can confirm the device does play music. After a minute it so the V+ resistor does got hot to the touch, but there is no smoke, no burned resistor smell, and it worked

I'm going to buy some 2W resistors, put that in and try not to destroy that one pad, then reconnect all the detached parts, and call it a job. Tons of thanks again for the help budm!

I am curious though, right now The only thing the V+ rail is supporting besides chips A-E is the LED light. Yet the V+ resistor is is still getting hotter than the V- resistor. So what is telling the syste to push more power through that resistor? Are the 3 transistors are always going to pull that 0.8W across that resistor, regardless of what is actually connected? If that is the case, then why aren't they doing that with the front board removed? Just for my education.

1) So what is the Vdrops on the 180 Ohms resistor without IC CD connected?

2) The regulator Transistors will only get hot when loads are connected.

3) We can balance the load for the +/- 12V by disconnected the Cathode of the LED from ground then use the same value of resistor on the Anode side, install the new resistor on the Anode side of the LED, then connect the other end of resistor to the - 12V. You can also reduce the current draw of the LED instead by using higher value resistor depends on how bright you want the LED to be.

4) Since the CD IC runs on +5V, you can run that IC from existing +5V power supply but we need to find out if the 7805 can handle extra load or not, some Voltage measurement has to be done first.

[SluggerB]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

1) So what is the Vdrops on the 180 Ohms resistor without IC CD connected?

I will check and post later on

2) The regulator Transistors will only get hot when loads are connected.

Makes sense. What I am curious about is right now, the only difference between V+ and V- in one LED. Is that extra load enough to heat up that V+ resistor while the V- resistor remains cool to the touch?

3) We can balance the load for the +/- 12V by disconnected the Cathode of the LED from ground then use the same value of resistor on the Anode side, install the new resistor on the Anode side of the LED, then connect the other end of resistor to the - 12V. You can also reduce the current draw of the LED instead by using higher value resistor depends on how bright you want the LED to be.

I do have plenty of spare 1/4th Watt resistors, I could put in a higher rated one. Since I'm putting a 2W resistor on the V+ line I want to keep the LED on that.

4) Since the CD IC runs on +5V, you can run that IC from existing +5V power supply but we need to find out if the 7805 can handle extra load or not, some Voltage measurement has to be done first.

I might just leave the CD IC and chips F & G disconnected. The owner confirmed he will never use the Mic input and following the traces those 3 chips seems to all be related to those functions.

[budm]

Re: Help diagnosing Pyle Receiver PTA66BT with burned resistors

"I am curious though, right now The only thing the V+ rail is supporting besides chips A-E is the LED light. Yet the V+ resistor is is still getting hotter than the V- resistor. So what is telling the syste to push more power through that resistor?:

The load dictates how much current it demands from the power supply, without E & F Opamp's connected, the resistor for the -V will be even cooler, the +V resistor will also get cooler than before.
As you can see 0.5W extra on the V+ feels like on the same mass and surface area of the resistor on the V- resistor.