I received a call from a customer who wanted her television checked by a technician.The complaint was the television had picture but no audio.
Upon reaching her home I decided to power on the television to confirm the symptoms and this is what I saw.
Besides having no audio, the picture has messed up colors, white lines across the top of the screen and finally no audio even when the volume was set at 100.
With that I concluded the television has three different issues.
I picked up the television to my workshop for further testing and repair.
After opening the television I noted the television quite old and usually with old equipment the components which age first are capacitors and also the board may develop dry joints.
I did proper re-soldering of any suspect areas and was happy.
Next i tested almost all capacitors on the board using ESR meter in circuit.
Whichever capacitor was suspect I would mark it on the board bottom side using a marker pen.
As you can see the above photo most of the faulty capacitors are around the main I.C and this explain why the television has those weird symptoms.
I later replaced all the faulty capacitor one by one and below you can see capacitors which were found with above normal ESR.
After replacing the capacitors I decided to see what effect that have to the television not forgetting a failed capacitor on audio circuit input or output can shut down audio completely and so I was optimistic that the audio may have been restored back.
After applying the power the television came up beautifully with clean picture and color and the white line across the top screen no more but audio still was not restored and this was the customer complain was and therefore I had to do further testing on the audio circuit.
First I had to confirm whether that audio ic (LA42205) was getting power or not.
I tested all the 15 pins of the ic and I got 15.63 volts on pin 9 and the rest of the pins had zero readings.
I touched the body of the audio ic and was cold like it was stored in a fringe.
Usually when ics are working they generate heat and usually become hot and that is why they always have heat sink to cool them down.
To advance my testing on this ic I needed now to get the datasheet for this ic LA42205 and I got the datasheet from the net as you can see application test below.
From the above you can clearly see pin.9 which I got 15.63 volts was actually the vcc pin and this means the ic was getting the supply voltage and therefore the ic should be working but that was not the case and therefore the only way to know if it is indeed faulty is direct replacement which I did and after replacement audio was restored back.
Thank you friends
See you in the next class
Hi Humphrey, what device do you use to test capacitor ESR in-circuit? Thanks!ReplyDelete
MESR-100 Pro ESR Digital Meter 100kHz In Circuit Tester Capacitor Ohmmeter.Delete
Can you do a blog entry that covers standby faults on both CRT and LED please?ReplyDelete
Voltage testing is the quickest and possibly the most reliable method of diagnosing a faulty equipment. Thankyou for sharing this vital information. I will order my ESR Meter in December.ReplyDelete
Thanks Mark for your feedback and interest on my products, all the best from the desk of Humphrey.Delete
Sanyo crt tv retrace lines no displayReplyDelete