Overheating Resistors on DAC board- "HELP NEEDED"

kkstereo · 5th February 2012, 03:03 AM

Hello, new here and needed for a tech advise on overheating resistors on a tube DAC. Here my "Dilema"

I have an California Audio Labs Tempest tube cd player (first edition,single chassis).
The problem is in the tube dac board, on left channel 2 parallel resistors (1.5k 4w each value) instant overheating(really hot) after ON and no output sound. I inverted resistors from left channel to right channel and problem still on left channel and tested out board both channel resistors and all measure 1.5k ohms, but installed the ones for left ch measure 6.750R instead 7.500R
The problen go after unit left for 2 days ON, and next time no sound and found the overheating resistors.
Looking what it is causing that overheating, I change new tubes and most electrolytic capacitors and nothing change. Revised carefully the rest capacitors for posible leak sign.Transformer and Bridge Rectifier measured that are OK.
So that my " DAC dilema"- SOS-HELP-AIDE-HILFE

Thank you in advance for any posible diagnostic.
Iincluded 2 photos of the board

DF96 · 5th February 2012, 03:42 PM

Possibly a short circuit somewhere? Do you have a schematic?

kkstereo · 5th February 2012, 10:12 PM

No I don't have schematics for this unit. You think that the Bridge Rectifier could cause that ? I must replace it, just in case.

kevinkr · 5th February 2012, 10:24 PM

Shotgun replacement of parts will not get you to the root cause of the problem. Most likely there is a failed component somewhere in the audio circuitry as these resistors appear to be cathode resistors or similar in an audio stage.

Have you replaced the tube on the bad channel to determine whether the problem is tube related? (Swapping not recommended) Have you measured and compared any of the voltages between the two channels?

Have you considered finding someone local with good troubleshooting skills and proper tools (scope, meters, etc.) to help you out? (Start here)

kkstereo · 5th February 2012, 11:10 PM

I replaced all tubes on both channels, about meassure the unit I just have basic knowlege and no the right meters tools, so I will take your advise and look a local tech to messured it properly.

Apreciated your time and advise, I will let you know when problem found.

5th February 2012, 10:24 PM	#4
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Shotgun replacement of parts will not get you to the root cause of the problem. Most likely there is a failed component somewhere in the audio circuitry as these resistors appear to be cathode resistors or similar in an audio stage. Have you replaced the tube on the bad channel to determine whether the problem is tube related? (Swapping not recommended) Have you measured and compared any of the voltages between the two channels? Have you considered finding someone local with good troubleshooting skills and proper tools (scope, meters, etc.) to help you out? (Start here) __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

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5th February 2012, 03:42 PM	#2
DF96 diyAudio Member Join Date: May 2007	Possibly a short circuit somewhere? Do you have a schematic?

5th February 2012, 10:12 PM	#3
kkstereo diyAudio Member Join Date: Feb 2012	No I don't have schematics for this unit. You think that the Bridge Rectifier could cause that ? I must replace it, just in case.

5th February 2012, 11:10 PM	#5
kkstereo diyAudio Member Join Date: Feb 2012	I replaced all tubes on both channels, about meassure the unit I just have basic knowlege and no the right meters tools, so I will take your advise and look a local tech to messured it properly. Apreciated your time and advise, I will let you know when problem found.