[Guest]

It could be power related, there are filter capacitors after the rectifier diodes and usually small electro's on the power in, of the IC's. It could be a bad solderjoint or hairline crack across a track. Maybe it is a faulty IC itself?
If you don't have a scope or ESR meter, maybe you could try replacing all of the electrolytics around all of the IC's? Or go over all of the solderjoints with your iron.
Replace all of the electrolytics around the verticle output IC heatsink. If one is right next to or inside of the heatsink mount it underneath the board if you have room.
If the front panel buttons plug into the main board, unplug them, lubricate the pins and re-insert the plug.
There is a site that may have some information or ideas that will interest you www repairfaq.org/sam/safety.htm
Good luck!

[Les Woollam]

I think I’m getting a little closer to nailing this one!
The TV now works kind of OK, but only prog change, text and standby work on the remote. . . the front panel switches do not work, but all ‘meter’ OK.
There is a slight lack of picture height.
I’m wondering if this could still be power supply related – possibly ‘dirty’ rails which still read the correct voltage?
Sound is OK, but volume cannot be adjusted.

[Guest]

These type of problems could be a dried up capacitor or a failing connection or even something else. You could spend hours checking all of the solderjoints with a microscope or testing all of the electrolytics with an ESR meter.
The voltage for the sound chip usually comes from the LOPT so if you get raster and no sound............ (it is not in the p/s circuit) [do you get the sound volume voltage?]
When the set is faulting you need to take waveshapes from various positions to give you a clue to where the problem is.

[Les Woollam]

Unfortunately, I have no way of measuring the EHT
The TV seems to have 'settled into a pattern'. . . on power-up, I get picture + sound (+ teletext!), but certain functions don't work. For example, the Prog and volume buttons on the front panel don't respond (Prog change on the remote works fine). On the remote, volume/menu/timer don't work.
This gets stranger by the minute

[Guest]

If the main PSU measures Ok. What does the Line Output Transformer measure like??

[Les Woollam]

OK, PSU seems to be OK - I was measuring the voltages using the incorrect earth as reference
All voltages are now virtually spot-on, apart from the 8VD rail which is measuring 12.4.
Back to the drawing board.. . any ideas????

[Les Woollam]

Thanks for all your help.
I've since discovered this is a PT92 chassis which, apparently, is used in many sets.

[Guest]

You could test them all to ground with your ohm meter...

Or remove the HOT, connect a 100 Watt globe from B+ to B+ ground, this will test the primary P.S.

[Les Woollam]

Many thanks for all the detailed pointers. . . certainly plenty to go on there!
I've since tested all PSU voltages, and they all seem to be sitting at around two thirds of the correct voltage - would this suggest maybe one of the rails being under too great a load thereby preventing the PSU from fully powering-up.?
Would it be OK to disconnect the rails one by one to test for this, or is there a risk of damaging any of the circuitry?

[Guest]

It is hard to know where to start. Does it make a sound like it is working hard or a light undervoltage sound? If it is working hard then you may have a short on one of the secondaries, which should be isolated before you power it up too often.
If you measure the mains filter capacitor you should get about 320Vdc, or a bit less depending on how much it is loaded. You can measure the ac voltage across this capacitor as it is only 100Hz, which should be no more than a couple of volts. If it is more than this then it may need replacement. Next to test is the B+ filter capacitor, you will need a CRO or ESR meter as this one travels much faster, maybe 15KHz. If you replace it, use a high temp (105 deg C) low ESR replacement. Then test the rest of the electrolytics in the power supply, usually there are two smaller ones sometimes in a heatsink where they overheat. Test all of the large low value resistors and high value resistors, you may have to remove them to get accurate results.
Remove the HOT and solder a light globe from B+ to B+ground, make sure you get it right or you will blow the powersupply if you energize it unloaded. If it is still low on volts, there is sometimes a regulator/switching multi-legged chip that switches the primary of the chopper transformer to regulate the B+.