memphis st1500

[timwebb]

i found it. it was a very tiny ball of solder stuck on some flux.

 

[timwebb]

ok. now it pules form red to green slowly.

 

[Perry Babin]

One board, both boards, boards in which location?

Is there DC pulsing on the output transistor tabs?

 

[timwebb]

Perry Babin;One board, both boards, boards in which location?

both board in both spots.

Is there DC pulsing on the output transistor tabs?

yes. about 30v.

 

[Perry Babin]

Do you have any DC on the tabs with the two driver boards removed?

 

[timwebb]

Do you have any DC on the tabs with the two driver boards removed?
nope.

 

[Perry Babin]

With neither driver board in the amp, solder a bridge between pins 13 and 14 of U105 on the audio PWM driver board. Do you have a square wave on 2 of the 3 pins of the 3-pin connector on that same board.

 

[timwebb]

time/div .5 time/div 5us

 

[Perry Babin]

Do you see the same signal on 2 of the 3 pins?

Is your scope calibrated? I would expect the peak to peak amplitude to be a bit more?

If you look at pin 9 of the TL494, is the square wave very nearly perfect? I'd expect this one to be more square but I don't know if it's your scope or the signal.

 

[timwebb]

Do you see the same signal on 2 of the 3 pins?
its on all three pins.

Is your scope calibrated? I would expect the peak to peak amplitude to be a bit more? i just did it.

If you look at pin 9 of the TL494, is the square wave very nearly perfect? I'd expect this one to be more square but I don't know if it's your scope or the signal. still the same.

 

[Perry Babin]

If that's from pin 9, there is a problem with either the scope, the probe or the calibration of the probe to the scope.

In post 20, I asked if the transformer was shorted primary to secondary. You stated that was and stated that you found it but were not specific as to what 'it' was. Is the primary to secondary short fixed?

 

[timwebb]

If that's from pin 9, there is a problem with either the scope, the probe or the calibration of the probe to the scope.

when i hook the probe up to the calibration on the scope. i get a clean square wave.

In post 20, I asked if the transformer was shorted primary to secondary. You stated that was and stated that you found it but were not specific as to what 'it' was. Is the primary to secondary short fixed?

it was a solder i think from my desolder pump that shorted the transformer out. its fixed.

 

[Perry Babin]

With no power connected to the amp, what's the resistance from the B+ terminal to the secondary ground?

 

[timwebb]

22k ohms

 

[Perry Babin]

Ground your scope to the secondary ground and re-check the signal on those 3 pins.

 

[timwebb]

all three pins have this same signal.

 

[Perry Babin]

Isn't one of those pins connected to the secondary ground?

When you post scope images, always include the settings.

 

[timwebb]

volts/div 5 time/div 5us

 

[timwebb]

had i slight ground issue. fixed it and its clear now.

 

[Perry Babin]

What's 'clear now'?

Do you read 0 ohms between any of the pins of the 3-pin connector and the secondary ground?

Where (precisely) did you connect your scope ground when you connected it to the secondary ground?