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What does this resistor do? - Crown PS-400

waggs098

waggs098

Super Member
Just wondering what the blown resistor in the pics does. The unit seems to work great and bias and dc offset are near spot on.

Want to replace the resistor but would like to know what it is for and what could possibly cause it to break like it did. There is no sign of smoke or burning and the resistor is open. Its a 2.7 ohm 2 watt resistor according to the service manual and it runs from +VCC to ground.

DSCN1789.JPG DSCN1790.JPG
 
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petehall347 said:
looks like a diode to me and goes to an insulated screw . what connects to the other end of the screw ?
Click to expand...

Its definitely a resistor. I found the pieces in the bottom of the unit. Its a funny looking connection but it is not insulated in any way. I read 0 ohms from the lead that looks insulated to the inside faceplate. Its R1 in the schematic and like I said connects from +VCC to ground.

Heres a pic of the pieces and the new resistor I have to replace it.

DSCN1792.JPG
 
if it is R1 2.7 ohms 1 watt ..its part of the grounding circuit..
it actually connects to 0v . right where the main filters connect together .
its the way i saw the pic that made it looked like glass .
 
According to the schematic its suppose to go from the circuit star ground to chassis ground.
 
petehall347 said:
if it is R1 2.7 ohms 1 watt ..its part of the grounding circuit..
it actually connects to 0v . right where the main filters connect together .
its the way i saw the pic that made it looked like glass .
Click to expand...

Ok I see. that makes more sense to me, looking at the schematic again. Not sure why I thought it connected to +VCC.
 
Ok got it replaced and left the unit idle for about 5 minutes and the resistor stayed cool. Guess ill put the amp in use and see what happens.

Could the old resistor just have been faulty and basically fell apart over the years?
 
heating and cooling with plain old age maybe did it . or a previously repair wasn't quite finished and was overlooked . hard to say . all that matters now it seems to be ok
 
What usually happens when that resistor becomes damaged, is when other audio gear is hooked up to it that has issues with it`s grounding, or connection to ground and a strong current flows through that resistor..

I`ve encountered it`s failure a few times over the years when repairing Crown DC 300`s that were brought in for other service, that were used in PA`s for local rock bands.

It helps with mild ground loops when the PA`s gear is close to being properly unity power grounded(common point/star).
 
Bill Ferris said:
What usually happens when that resistor becomes damaged, is when other audio gear is hooked up to it that has issues with it`s grounding, or connection to ground and a strong current flows through that resistor..

I`ve encountered it`s failure a few times over the years when repairing Crown DC 300`s that were brought in for other service, that were used in PA`s for local rock bands.

It helps with mild ground loops when the PA`s gear is close to being properly unity power grounded(common point/star).
Click to expand...

Agreed, this is the classic description of a ground loop. This happens with band's gear and is why there's a ground reverse on many guitar amps. I've been bitten more than once touching a mic and any other piece of the band's gear. Playing sax is a bit safer than those poor guitar players!

Cheers,

David
 
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