This
TV was brought in my shop with the picture ok but the sound was not
stable…sometimes good and other times not.
I
opened the set and went straight to the speaker (power off and power cable disconnected
from the power outlet).
Checking
on the speaker label I noticed the speaker was rated 8 ohm and a quick test
with my ohmmeter got 8 ohms…this confirmed to me that the speakers are okay and
therefore I should look elsewhere for the problem.
So the next hypothesis considered for checking is the sound amplifier ic and
since I did not have the circuit diagram of this TV, I decided to look up for
the sound amplifier ic, To know which is which I followed the speaker wires
backward from the pins of the speaker to the main pcb and followed closely the PCB
lines and this directed me to an ic TDA 7245.
I
did a Google for this IC TDA 7245 for the datasheet and here what I got.
Looking
at the circuit you can see pin 3 is very important because it is the power
supply pin. I set my meter on 100 VDC range and did a voltage testing on this pin
with my meter red probe on the pin 3 and black on cold ground.
To
my surprise the Voltage was well within my expected because from the datasheet
I was able to see that this IC needs a working voltage between 14 VDC minimum
and 30 VDC maximum.
Up
to here things are ok, now what else? I decided to check for the signal output
for the presence of a signal using a scope and if found no signal and I concluded
that the IC TDA 7245 must be the culprit.
Below
you can see the pin connection of this IC
I
replaced the IC with a new one and after applying the Power I loved what my ears
heard…very nice sound…
This
Report is brought to you Courtesy of Mr. Beh.
A
renowned Technician of all time
City:
Tehran Country: Iran
Mr
Beh can be contacted directly at email: bsedigh@yahoo.com
HI MR KIMATHI
ReplyDeletei want add to this report that there is no any voltages in the pin no 2 ic to check and find out that ic is good or bad but with scop we can check the RF signals that are coming form the ic or not?
regards
beh
Thanks a lot for this very helpful topic....just want to ask,what is the very typical specs of scop that a technician needs have in his bench? Thanks
ReplyDeleteHi Bogie, check out this link on what to consider when buying a scope.
ReplyDeletehttp://www.picotech.com/applications/oscilloscope_tutorial.html
Regards Humphrey
Nec crt tv, no power, green led on, but no picture, copper trnsformer not out voltage.
ReplyDelete