power 8004

[Perry Babin]

With no signal in, is there any DC (more than a fraction of a volt) on the distorted channels?

 

[megael9]

Voltage looks ok, all channels have
about .067 volts

 

[Perry Babin]

Compare the voltages measured directly across Rx20 and Rx21 for the good and defective channels. Are they similar? If not, how much difference is there between them?

 

[megael9]

R20 is 0 volts
R21 Is 2.2 volts.

 

[Perry Babin]

Not R20 and R21.

 

[megael9]

R121 =0.653v
R120 =0.616v

R221 =0.647v
R220 =0.615v

 

[LAJ]

Just remember what a wise old engineer once told me. If it worked before, it can work again.

 

[Perry Babin]

If that's from one good and one distorted channel, it would appear the the problem is beyond the differential amp.

Do you have a scope?

 

[megael9]

Yes I have a scope, and
yes the voltage reading
is from a good and a bad
channel. a I also have the
test tone cd, I purchased
from the sitein case it help
Troubleshooting
it help.

 

[Perry Babin]

Connect a speaker load to the amp and drive a 100Hz test tone into it. Set the scope to 2mS/div and 5v/div and drive the output to deflect to ±2 divisions on a good channel. Switch to a distorted channel and post a photo of the distorted waveform.

I can't remember what equipment you have (scope, meter, power supply...). To save time, please list them in your sig file. Others should do the same if they're asking for help repairing amps.

 

[megael9]

I looked, but did not found where to
get to my sig file, for the equipment
list, by the way this is my list.
fluke 97 50 mhz,
fluke 87
fluke179
piramid 35amp power supply
adjustable 0.5-12 volts power supply
merit signal tracer/generator
and a air desolder gun.

 

[Perry Babin]

The 'user CP' link at the top of the page will allow you to edit your sig file. The sig file is limited to 1 or 2 lines so you'll have to reduce the text size and/or abbreviate the list. The scope, meter, ps and generator are probably the most important items.

 

[megael9]

I looked for the the sig file section
for the equipment list, but did not
found it, by the way my equipment
list is as follow
fluke 97 50 mhz
fluke 87
fluke 179
piramid 35 amp power supply
0.5-12 adjustable power supply
merit multyfuntion tracer/ generator

 

[Perry Babin]

Get the photo of the waveform posted.

 

[megael9]

which will be the test points
for the scope?

 

[Perry Babin]

The speaker terminals.

 

[megael9]

sorry, but there was almost near nothing
when test with div 2-5v, perform the test
using 100mv, and this is what I get.
the 1st image is the bad channel.

 

[Perry Babin]

Is this one good channel and one bad channel?

Is this with a 100Hz sine wave?

Did you have both probes for the scopemeter directly on the speaker terminals?

 

[megael9]

yes it`s a good and a bad channel, the probe
was connected directly to the speaker terminal
with one speaker connected to the tested channel
Im using 100hz sine wave #19 of the cd,
and using the power supply ground

 

[Perry Babin]

I don't see a good signal in either photo. Are you sure that your scope is working properly?

Will it display a clean signal if connected across the signal source?