Check other parts then.ballfire wrote:
any advice?
90% of every repair is diagnostics.
It is not quite as easy as you telling us which resistor is getting hot and that the sound has changed for us to be able to tell you how to fix your amp.ballfire wrote:any advice? please anybody around here..until this time i cannot fix my amp..the fatiness of my amp lost..
deltafred wrote:It is not quite as easy as you telling us which resistor is getting hot and that the sound has changed for us to be able to tell you how to fix your amp.ballfire wrote:any advice? please anybody around here..until this time i cannot fix my amp..the fatiness of my amp lost..
I have already given you my diagnosis from the very limited information that you have given us but I may be completely wrong because I don't have your amp on my bench.
To confirm whether it is oscillating above the audio frequency range you would need to look at the output waveform with an oscilloscope.
If it is oscillating then the next challenge is to find out what is causing it. This could be a bad solder joint or a component out of spec, including the output IC and those in the power supply.
deltafred wrote:Can you measure the voltage that is across the smoothing caps, the voltage across the zener diodes and the voltage across the 220 ohm resistors, and post your findings here.
I still think it is oscillating above the audio frequency range, disconnecting the speaker will have an effect on that.ballfire wrote:During my test i detach the speaker of my amp desolder the wire positive and negative terminals
when i turn on the amp ,i notice that the one large 2200 uf at -V rail didnt get much hot just a little warm..the other 2200 uf didnt even get hot..
phatt wrote:At a guess the Bridge rectifier may have a blown diode,, That would heat up the Cap.
Also Check that the negative Cap is connected the right way round,, i.e. Positive to Common Rail.
Phil.
ballfire wrote:phatt wrote:At a guess the Bridge rectifier may have a blown diode,, That would heat up the Cap.
Also Check that the negative Cap is connected the right way round,, i.e. Positive to Common Rail.
Phil.
the orientation of that heated capacitor is just like the marshall power supply i posted above..i think its right..
what do you mean" Check that the negative Cap is connected the right way round"
>>>do you mean i will reverse the 2200 uf the negative side to the ground now not on the -V rail side??
if the diode bridge is the problem can i use a 2 ampere diode bridge??instead of 4 ampere??
thanks
deltafred wrote:I still think it is oscillating above the audio frequency range, disconnecting the speaker will have an effect on that.ballfire wrote:During my test i detach the speaker of my amp desolder the wire positive and negative terminals
when i turn on the amp ,i notice that the one large 2200 uf at -V rail didnt get much hot just a little warm..the other 2200 uf didnt even get hot..
Check the 1 ohm and 0.22uF (R5 and C5) connected to the output pin 4 in the schematic below. If either of these are faulty the circuit will oscillate. (This is a typical schematic taken from the datasheet so some values may be different).
deltafred wrote:As Phatt says, check for bad solder joints and cracked copper tracks especially where a track joins a solder pad.
Phatt. I was thinking about one of the diodes in the the bridge rectifier being faulty but that would probably affect the cap voltage.
No! You should not reverse it.ballfire wrote: by the way this cap always heating up can i reverse this cap ??? maybe i should reverse it maybe its the problem....see picture below
plush wrote:The main crap-feature of your power supply is that the output voltage is "stabilized" using zener diodes, they are prone to adding noice to your power section and, due to their pretty high tolerancy, they don't provide symmetrical bipolar voltage.
If I were you, I'd redesign the whole power section using low voltage drop regulators, similar to lm7812 and lm7912.