I was trapped into fixing Mrs Cartland’s Philips CR635 TV set. This set is over 10 years old and of course I am familiar with the old Australian-made KL9-A3 (and KT3A-3) chassis which, in my opinion, were very well built. And I say "trapped" because I try to steer clear of such old sets but she laid on the flattery and praise – tactics to which I’m quite susceptible.

There was no sound or picture, although it was hiccuping or motorboating, the sound coming from the speaker. However, it didn’t seem to be quite the same kind of motorboating sound that comes from a faulty audio amplifier circuit. Instead, I felt that it was more likely to be a faulty tripler or horizontal output transformer and so I agreed to have a look.

First, I disconnected the tripler (1570) but it made no difference. I then removed the horizontal deflection plug, which also links the 140V rail to the horizontal output stage (plug/socket 4M5/2M5) and measured test point M2 (marked on the board but not the circuit) to check the voltage there. This voltage had previously been pulsating but was now steady. Next, I shorted the base and emitter leads of the horizontal output transistor (7562). There was still voltage (335V no load condition) but again, the pulsating stopped.

Most of the noise was coming from the loudspeaker and by turning down the bass and treble controls this could be stopped, but the horizontal output stage could still be heard hiccuping or pulsating. All I had proved was that there were no DC shorts on the main supply rail but there could be a problem within the inductive load of the horizontal output transformer circuit.

It was at this stage I realised that the set had to go to the workshop. This was a nuisance but Eileen’s praise for my technical skills somehow made it all worthwhile.

To settle any lingering doubts, I fitted a new horizontal output transformer (5564) which made no difference. I also disconnected the deflection yoke without removing the voltage rail links and ran it very quickly to see if there was any change (I didn’t want to incur screen burn from the dot) but there wasn’t. Having eliminated these two major items, I also unplugged the CRT socket in case there were any shorts inside the tube.

In order to check the main HT rail, I connected a dummy load (consisting of a 100W globe) from the collector of the horizontal output transistor to chassis and again shorted its base to emitter. This time the voltage read a steady 141V on M2, which was what I was hoping for. I then checked R3561, the limiting resistor to the base of the horizontal output transistor, as well as all the components in that circuit.

I was beginning to think that there was a problem on the secondary side of the horizontal output transformer (5564) and so I decided to disconnect each pin, one by one, and check the effect. Disconnecting pin 18 restored the HT without it pulsating. This pin supplies three 32V rails and the significant one was 32b, to pin 10 of the sync IC (7375, TDA2577), which should be at 12.3V.

By disconnecting this one leg I could get sound and horizontal deflection but no vertical deflection. I now felt sure that this was where the trouble was (ie, around IC7375) and I spent a lot of time trying to find a fault in this IC or the circuits connected to it.

As far as I could work out, its pin 10 was a secondary supply that was switched on following the start-up voltage (10.6V) being applied to pin 16. But I could not see what effect it could have had on the vertical time-base. Eventually, I forced myself to stop thinking about IC7375. I had already disconnected all of its pins to no avail.

Sets Covered This Month Philips CR635 TV set Mitsubishi HS621 VCR Mitsubishi HS-M60 VCR National M15L TV set