Items Covered This Month JVC AV29LS TV set (CH chassis) Sony KV218SAS TV set (G3E chassis) Various computer repairs Blaupunkt FM310.32 / Grundig CUC5360 TV set

Mr Bronwyn needed some help getting his 2001 JVC AV29LS (CH chassis) out of the car. That’s because this particular JVC model is a bulky and heavy flat screen job, while his sedan was small and elderly to boot – rather like himself. Nevertheless, we managed.

He complained that his set had no picture, just a white line across the screen. In this case, however, the white line was across the bottom of the screen and not the centre, which was rather unusual.

I started with the vertical output IC (IC41, LA78041) and the oscilloscope quickly told me there were no vertical pulses arriving on pins 1 (VDRB-) and pin 7 (VDRA+). Brushing my fingers along the pins of the IC momentarily produced a small movement in the vertical deflection, so I was pretty sure the fault didn’t lie here.

Next, I traced the signal path back to pins 21 & 22 of the microcontroller/jungle IC (IC701) but there was still no signal. This indicated that IC701 itself was the likely culprit. The only trouble was that this 64-pin device (TAD9365NI3S0572) costs $123.30 trade plus freight, so before removing it, I decided to check the DC voltages on it to confirm my diagnosis.

First, I measured +3.3V on pins 54 & 56 of the microcontroller section, which is correct, but I found only +5V on pin 14 of the jungle section, whereas this should be at +8V. I traced this rail back to the power supply and found it came out on pin 1 of IC974, a composite switchable IC regulator (BA51W12ST-V5). This should have read +9V before feeding R957 and D955 to produce the 8V rail but instead, the voltage here was low.

The regulator IC is in turn supplied with +9.6V to pin 2 via resistor R969 (2.7W) and this voltage was also low. However, the other side of the resistor was at +13V!

A quick check confirmed that resistor R969 had gone high. And as might be expected, replacing it brought all the voltages up to normal and restored the vertical deflection.

Of course, all this was relatively easy compared to trying to stuff the telly back into Mr Bronwyn’s car!