Item's Covered This Month NEC FS-68T90 TV set (Daewoo CP-785A chassis) Sony TA-EX70 AV Centre Control Amplifier Sony KP-EF41SN (RG-2 chassis) projection TV Denon UDM50 stereo system Loewe 84-100 TV set (Q2100 Chassis) JNL5103 TV set Sharp CX6N5 TV set Blaupunkt IS70-33 TV set

Mr Patrick brought in his dead NEC FS-68T90 (Daewoo CP-785A chassis) just after an electrical storm the night before.

As usual, the fuse hadn’t blown and most of the set looked perfectly OK. Powering it up, everything seemed correct except for a low 5V rail.

By disconnecting the circuits bit by bit, I soon found that the tuner (Philips) was drawing excess current due to an internal short. Replacing it removed this short and restored the 5V rail. However, there was still no EHT because there was no horizontal drive waveform from the TDA9365 jungle IC.

The voltages all looked correct apart from the ones which were dependent on the line output stage working – even the crystal frequency was spot-on. However, the DC voltage on the I²C SCL clock pulse was low, with no data activity showing on the CRO.

Once again, by progressively disconnecting all the ICs the SCL pulse went to, the Sound Micron microprocessor IC601MSP3451D was determined to be the culprit. A new one restored almost everything in the set, with good picture and sound. What still didn’t work was the install menu and the service manual didn’t give much of a clue on this.

NEC Technical Support thankfully deduced that the set was locked into the "HOTEL" mode. This function is to protect hotel TV installations from the prying hands of inquisitive guests. To release it, you have to press "Delete", "Move", "Skip" and "Operate".

Finally, to access the Service Mode, you must first select program 91 and set "Sharpness" to minimum, then very quickly press "Red", "Green" and "Menu" in turn, then "OK".

In summary, it looked as though Mr Patrick’s TV had suffered a lightning strike via the outside aerial. This damaged the tuner, before sending a transient back up the SCL clock pulse line. Under the circumstances, it could have been much worse.