JVC image dark, normal OSD and sound

This TV comes with symptoms: a dark image but the OSD (On Screen Display) and Normal Voice. If you've had, this is exactly like the damage that often occurs in TV Sony Chassis BG-2S caused the ABL resistor open.
But despite its symptoms look the same, but the cause is completely different.

Initially we also thought that the damage must be on the ABL, but After measurements were taken both on the voltage and its supporting components reveals no problems in this area of ​​the ABL.



Then we did the measurement of the voltage on each pin on IC201 (TB1226EN) and we compare it with the reference voltage on the data sheet IC TB1226EN, finally discovered that the pin 21 (YS) there are voltage spikes up to 2 volts than it should be by 0.3 - 0.5 volts .

Where Pin # 21 of TB1226EN serves as a control switch (mixer?) Between OSD RGB signals (digital) from Micom and RGB signal from Croma jungle (analog), based on its operating manual, if Pin 21 is given a voltage of 2 volts, then swith fully connected to the OSD RGB signals, and if the voltage is lowered to 0 volts, then the switch is fully connected to the RGB signal from the Croma.

So when Pin # 21 Our short-circuit to ground (on the right-zero), then the picture looks but OSD meghilang, conversely when a short circuit to ground us off, OSD back but the picture looks darker again.

Next we perform a search to find what the cause of the voltage Pin 21 TB1226EN up to 2 volts than it should be 0.3 - 0.5 volts, and we found that the control pin of the IC Micom number M37212M8-050SP was the cause, because this pin (pin No. .49) removing the voltage to 6 volts than it should be 0.3 - 0.5 volts, so we conclude that the IC Micom damaged.

But, before we decided to completely replace its IC Micom, we try to check every item of its service menu there is probably a wrong setting its parameters, and as usual before we change it, we did it prior EEPROM data backup just in case if an error occurs so it is easy to restore the original condition, and also for the purpose of sharing data eeprom perhaps fellow member beteve.com technician there who need it.

After we finished eepromnya data backups, then we open up its service menu, which is using a JVC TV-1 Code Key to open it, that is by pressing and holding the DISPLAY button on the remote followed by pressing the PICTURE MODE button on the remote as well, but it would surprise us, turns out when we were pressing the DISPLAY button, the image instantly appears normally.

To ascertain whether the right because we are pressing the DISPLAY button and then the TV to normal or whether for other reasons, we try to rewrite (rewrite) data that we have eeprom backup and the pair returned to the chassis, and it turns out the data from previous backups's TV return to its original state, but the OSD is a dark image and her voice is normal, then when we press the DISPLAY button, the image instantly appears with the normal.

We then compared the data from the eeprom when dark images and current conditions to normal conditions, and it is known that there are differences in the data at offset 00h in normal conditions where offset 00h contain data 21h, but when conditions are dark images, offset 00h 31h unallocated.

So his conclusion is the damage with symptoms of dark images and sounds normal but the OSD on the JVC model AV-K14T2 this (and of course also applies to other models based on the same chassis) is caused by eeprom data of persons with disabilities, and not caused by Micom IC, IC Croma or ABL problematic, an unexpected coincidence.