Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

[fuxxy]

This is my wife's set of computer speakers.
Earlier today, we noticed an odd smell in the computer room, and diagnosed it to her speakers. The plate amp was HOT!!. Much, much warmer than my speakers, of the exact same model.

Opened it up, and was greeted immediately with two overheated 1W resistors on the sub amp/power supply board.

Odd that this amp was so hot considering it had been in standby. No use at all today.

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

Removed the daughterboard from the PSU.

Any ideas what would cause these resistors to get so hot?

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

schematic for LF amplifier (courtesy of Dale Thompson)

[budm]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

Do you know what the +V_LF Voltage is?
Did you check those two 15V Zener to see if they are OK?

[R_J]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

Does the amp still work at all? The resistors drop the voltage from the plus and minus V_LF
Do what budm said, then check the voltages on the 2 zeners,
Then check the 2 resistors that burnt and see if they actually are open, looks like they have been running hot for a while and maybe they just finally opened up. I suspect their wattage could be under rated or just poor quality resistors
If you replace them and they still get hot I would suspect a damaged TL074 ic. I would also replace c09 & c11

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

budm, R_J
+V_LF voltage is 48.8vdc
-V_LF voltage is -48.9vdc

R16 and R17 Both read 1k ohm (removed from board)

The zeneers (D03, D04) read good in voltage drop mode.
D03, .667 voltage drop, open reverse polarity
D04, .583 voltage drop, open reverse polarity

R_J,
I don't know if the speakers currently work. We unplugged them as soon as we thought they were what was making the smell. I had noticed in the past that her speakers didn't put out nearly as much bass as mine did though.

[budm]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

You need to check the actual Voltage between the two legs of the Zeners to see if they are 15V or not.
The power dissipation of the resistor with 15V Zener is about 1W.

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

D03 is 15.81
D04 is 15.6V

I had to google how to test, lol. Never messed with zeners before.

They seem to be climbing, though. In the time it took to post this:
D03 is 15.94
D04 is 15.81

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

After an hour -

D03 is 16.08
D04 is 15.93

[budm]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

After an hour -

D03 is 16.08
D04 is 15.93

That is within the spec. It will be bad if they show low reading which will mean more Vdrops on the resistors which will generate more heat.
I am going to guess that there is no ventilation for the boards in that cabinet, right?
1W of heat for each resistor can be very hot in very poor ventilation.

[rhomanski]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

For the 5.1 it's been recommended for years to mount a fan blowing on those two resistors. I put one in mine back in 2007. It's had no problem since. A small fan and some zip ties. Others have gone so far as to take the back panel off replace with a blank panel and build a ventilated cabinet for the electronics. Also I keep it turned off unless I want to listen to something.

[momaka]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

I see a lot of solder joints with what appears to be small ring cracks in these pictures:
https://www.badcaps.net/forum/attach...4&d=1490670049
https://www.badcaps.net/forum/attach...8&d=1490670631

I suggest redoing all of the solder joints first and then check if the speakers work again.

[Andrew F. Ali]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

Is the speaker impedance OK? Guessing it may be 3-4ohms. Were the driver and output transistors tested?

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

The speakers worked, however they did not sound nearly as "strong" as my set.

R_J, the only 100uf caps I have at the moment are "Jamicom". I don't have a capacitance meter, would you trust that brand?

momaka, would you mind pointing out some of the bad joints you saw? I'm having a hard time seeing them in person, and would like to make sure.

Andrew, the speaker resistance is 5 ohms, The best guess at original OEM impedance is 6 ohms.

[fuxxy]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

Andrew, I did a simple short test on Q06 and Q07, and all three legs read open no matter what polarity.

I'm not sure how else I would test them

[momaka]

Re: Klipsch ProMedia 2.1 Amplifier is HOT!!! and bad smell in room

momaka, would you mind pointing out some of the bad joints you saw? I'm having a hard time seeing them in person, and would like to make sure.

Sorry for the delay in response.

On this picture,
https://www.badcaps.net/forum/attach...8&d=1490670631
the solder joints on capacitor C12 look absolutely terrible. Also, the ones on resistor R21 don't look great either.

And on this picture,
https://www.badcaps.net/forum/attach...4&d=1490670049
the joints on connector P102 (top-right of picture), and many of the small components on the lower-middle of that picture also appear to have ring crack. Perhaps, it could also be the flash from your camera... but to be honest, I think the soldering looks poor on those boards, and I would redo as many joints as possible, just to eliminate that as the issue.

Just grab a bottle of rosin flux, apply on the board, and with a tiny bit of solder on your soldering iron's tip (preferrably leaded solder), just reflow the joints.

Andrew, I did a simple short test on Q06 and Q07, and all three legs read open no matter what polarity.

I'm not sure how else I would test them

Those should be BJT transistors, if I am not mistaken... though it would help if you provide us with part numbers.

For BJTs, you just have to know/find the Base pin and whether it's a PNP or NPN. Typically, the Base pin is the leftmost one for TO-220 and larger devices - that is, with the transistor part numbers facing you. Then, middle should be Collector, and rightmost pin Emitter.

For NPN, you should get a diode reading on your multimeter when positive (red) probe is connected to base and negative (black) probe is connected to either Collector or Emitter.

For PNP, you simply reverse the leads.

Getting open-circuit no matter which way you have the leads may suggest open transistors (sometimes, BJT transistors can blow up so hard, that they go open-circuit).