Faulty Kat5 Tx

[ianh100]

Hi Keith

I have an early Kat5 tramsmitter with IR upgrade, it seems to have gone bad. I swapped it out for a spare (without the IR upgrade) so I know the fault is in the transmitter.

Not quite sure how to describe the fault. The video signal appears very dark, mostly red and the audio is very distorted. Any suggestions on how to fault find? If not I guess I just move the IR upgrade board over to my spare.

As a second question the IR remote was working but it was intermittent when the IR transmitter was pointed directly at the rx eye. if I point the transmitter at an angle it was much more reliabale. This is be used for remot Tivo control ( only for a few more weeks).

Thanks

[katman]

Hi Ian,

Sounds like either a video opamp has failed or the power supply within the unit it faulty.

Does if work OK is the IR upgrade is unplugged ?

Check the voltages as follows, put the multimeter negative lead on a ground point, the tab of U901 is the most convienient place.

on the metal tab of U903 you should have around -10 volts or slightly more. If this is a lot lower or non existant then U902 the voltage inverter has probably died. ICL7660A As the audio is also distorted my guess is a power supply fault.

If that is OK, check the voltages on pins 8 and 4 of the opamps. Pin 8 should be +5v, Pin 4 should be -5V

There should be no noticable DC offset on the outputs of the opamps, pins 1 and 7, they should normally be under 20mV. If there is a large offset voltage then the opamp is probably faulty. The video opamps are AD828's and the audio opamps are NE5532's

All ICs are socketed so swapping them over is easy.

If you want to send it back I will take a look at it for you.

Dont give up on Tivo just yet, work is underway on an alternative EPG and I am hopeful that my spare unsubbed Tivo will be given a new lease of life as well

Regards

Keith