Help with B&O LX4500

[LXSTEIN45]

Hi folks am wondering if someone would be prepared to share their experience and help me with this classic (IMO ) telly?

Basically I have replaced a shorted HOT for a no power fault. Checked all the associated components i.e. diodes / tuning capacitors all appear to be within tolerance using my meter - Not sure about high volts performance atm though..

Disconnected all LOPTx terminals apart from 'EHT ON' / associated ground and of course the primary coil and high voltage terminals. Attached 60W lamp between LOPT and HOT.

Now the green led comes on, improvised bulb flashes initially, then telly goes back into standby but that is all I have got so far!

So moving on, to check LOPT etc. I made a Bob Parker ring tester here.

Yoke tests fine (base mounted resistors not shown on cct threw me off initially!), LOPT 'primary' is fine but all of the secondary windings are not really registering. There is a split winding that registers across the extremes but again nothing from centre tap to either end. Not sure if this would be normal for this LOPT or whether it is indicative of my problems? Absolutely no externals signs of damage / discharge but maybe the PSU responding to fault so quickly has prevented such damage?
Oh, HT and focus nothing shows as if o/c, I assume correctly!

Now my lack of experience, and not having a replacement LOPT is why I am reluctant to take things further, and of course, I am blindly assuming LOPT and associated parts might be still available!

It seems a shame to get rid of what I think is still a really nice telly, and while I don't want to spend too much money on it, time is not a problem!

So folks, I am hoping either direct experience of this chassis or at least your guidance can take me a little further?!

Regards,

Olly.

[Maarten]

Normal procedure (though sometimes destructive on the new HOT), is to check the drive circuit (dry joints, electrolytics) then the load (ringing the LOPT primary, measuring diodes for shorts, finding suspicious foil capacitors, dry joints). Additionaly, the main power supply can be tested under the load of a light bulb. If nothing is found or problems are corrected, the set is powered on.

At this stage, powering on the set with several things disconnected doesn't really make sense.

[LXSTEIN45]

Hi, thanks for your response. I have checked all above but the PSU and drive circuitry I will have another go sometime during the following week!

Thanks!

Any further tips from someone who knows this or similar chassis would be appreciated

Olly.

[Studio263]

You need to put the set into service mode and disable the "power fail" ring if you want to make tests like this, get the manual off the internet to read more about it. Try pressing <AV> <Radio> from standby on the Beolink 1000, this puts the set into audio mode where the power supply will run (if it is able to) even with the line output transistor removed.

There are two versions of the bottom panel used in this chassis, the later one has a conventional line driver stage, the former a horrid DC coupled affair like the one in the previous LX2502. These have an electrolytic in series with the BU508A base (220uF of thereabouts), change this and the transistor, it should have a chance of working then. I've never changed a LOPT in one of these so you should be OK with that.

[LXSTEIN45]

Hi Studio263 thanks for that busy at the moment but will let you know how I get on when I get a spare minute